Bacillus: A Biological Tool for Crop Improvement through Bio-Molecular Changes in Adverse Environments

Impact of cultivating different Ocimum species on bioaerosol bacterial communities and functional genome at an agricultural site

The effects of the surrounding environment on the bacterial composition of bioaerosol were well documented for polluted and contaminated sites. However, there is limited data on the impact of plant species, especially those that produce aromas, on bioaerosol composition at agricultural sites. Hence, the aim of this study is to evaluate the variability in bacterial communities present in bioaerosol samples collected from agricultural sites with aroma-producing crops. For this, PM2.5, PM10, and bioaerosol samples were collected from agricultural fields growing Ocimum [two varieties of O. sanctum (CIM-Aayu and CIM-Angana)] and O. kilimandscharicum (Kapoor), nearby traffic junctions and suburban areas. PM2.5 and PM10 concentrations at the agricultural site were in between the other two polluted sites. However, bioaerosol concentration was lower at agricultural sites than at other sites. The culturable bacteria Bacillus subtilis, Bacillus tequilensis, and Staphylococcus saprophyticus were more prevalent in agricultural sites than in other areas. However, the composition of non-culturable bacteria varied between sites and differed in three fields where Ocimum was cultivated. The CIM-Aayu cultivated area showed a high bacterial richness, lower Simpson and Shannon indices, and a distinctive metabolic profile. The sites CIM-Angana and CIM-Kapoor had a higher abundance of Aeromonas, while Pantoea and Pseudomonas were present at CIM-Aayu. Acinetobacter, Staphylococcus, and Bacillus were the dominant genera at the other two sites. Metabolic profiling showed that the CIM-Aayu site had a higher prevalence of pathways related to amino acid and carbohydrate metabolism and environmental information processing compared to other sites. The composition of bioaerosol among the three different Ocimum sites could be due to variations in the plant volatile and cross-feeding nature of bacterial isolates, which further needs to be explored.

The Combination of Biochar and Bacillus subtilis Biological Agent Reduced the Relative Abundance of Pathogenic Bacteria in the Rhizosphere Soil of Panax notoginseng

In the continuous cropping of Panax notoginseng, the pathogenic fungi in the rhizosphere soil increased and infected the roots of Panax notoginseng, resulting in a decrease in yield. This is an urgent problem that needs to be solved in order to effectively overcome the obstacles associated with the continuous cropping of Panax notoginseng. Previous studies have shown that Bacillus subtilis inhibits pathogenic fungi in the rhizosphere of Panax notoginseng, but the inhibitory effect was not stable. Therefore, we hope to introduce biochar to help Bacillus subtilis colonize in soil. In the experiment, fields planted with Panax notoginseng for 5 years were renovated, and biochar was mixed in at the same time. The applied amount of biochar was set to four levels (B0, 10 kg·hm-2; B1, 80 kg·hm-2; B2, 110 kg·hm-2; B3, 140 kg·hm-2), and Bacillus subtilis biological agent was set to three levels (C1, 10 kg·hm-2; C2, 15 kg·hm-2; C3, 25 kg·hm-2). The full combination experiment and a blank control group (CK) were used. The experimental results show that the overall Ascomycota decreased by 0.86%~65.68% at the phylum level. Basidiomycota increased by -73.81%~138.47%, and Mortierellomycota increased by -51.27%~403.20%. At the genus level, Mortierella increased by -10.29%~855.44%, Fusarium decreased by 35.02%~86.79%, and Ilyonectria increased by -93.60%~680.62%. Fusarium mainly causes acute bacterial wilt root rot, while Ilyonectria mainly causes yellow rot. Under different treatments, the Shannon index increased by -6.77%~62.18%, the Chao1 index increased by -12.07%~95.77%, the Simpson index increased by -7.31%~14.98%, and the ACE index increased by -11.75%~96.12%. The good_coverage indices were all above 0.99. The results of a random forest analysis indicated that Ilyonectria, Pyrenochaeta, and Xenopolyscytalum were the top three most important species in the soil, with MeanDecreaseGini values of 2.70, 2.50, and 2.45, respectively. Fusarium, the primary pathogen of Panax notoginseng, ranked fifth, and its MeanDecreaseGini value was 2.28. The experimental results showed that the B2C2 treatment had the best inhibitory effect on Fusarium, and the relative abundance of Fusarium in Panax notoginseng rhizosphere soil decreased by 86.79% under B2C2 treatment; the B1C2 treatment had the best inhibitory effect on Ilyonectria, and the relative abundance of Ilyonectria in the Panax notoginseng rhizosphere soil decreased by 93.60% under B1C2 treatment. Therefore, if we want to improve the soil with acute Ralstonia solanacearum root rot, we should use the B2C2 treatment to improve the soil environment; if we want to improve the soil with yellow rot disease, we should use the B1C2 treatment to improve the soil environment.

Cereals can trap endophytic bacteria with potential beneficial traits when grown ex-situ in harsh soils

Microbial communities associated with plants growing in harsh conditions, including salinity and water deficiency, have developed adaptive features which permit them to grow and survive under extreme environmental conditions. In the present study, an ex-situ plant trapping method has been applied to collect the culturable microbial diversity associated with the soil from harsh and remote areas. Oryza sativa cv. Baldo and Triticum durum Primadur plants were used as recruiters, while the soil surrounding the roots of Oryza glaberrima plants from remote regions of Mali (West Africa) was used as substrate for their growth. The endophytic communities recruited by the two plant species belonged to Proteobacteria and Firmicutes, and the dominant genera were Bacillus, Kosakonia, and Enterobacter. These endophytes were characterized by analyzing some of the most common plant growth promoting traits. Halotolerant, inorganic phosphate-solubilizing and N-fixing strains were found, and some of them simultaneously showing these three traits. We verified that 'Baldo' recruited mostly halotolerant and P-solubilizers endophytes, while the endophytes selected by 'Primadur' were mainly N-fixers. The applied ex-situ plant trapping method allowed to isolate endophytes with potential beneficial traits that could be applied for the improvement of rice and wheat growth under adverse environmental conditions.

Transcriptomic analysis of the response of Avena sativa to Bacillus amyloliquefaciens DGL1

Introduction

Bacillus amyloliquefaciens DGL1, isolated from the arid sandy areas in Dagler, Qinghai Province, China, promotes the growth of Avena sativa variety "Qing Yan 1".

Methods

To elucidate the transcriptomic changes in the oat root system following interaction with DGL1 and to reveal the molecular mechanism by which DGL1 promotes oat growth, treatment and control groups of oat roots at 2, 4, 8, and 12 h after inoculation with a suspension of strain DGL1 were analyzed using Illumina high-throughput transcriptome sequencing technology. The differentially expressed genes were determined through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses, and the metabolic pathways and key genes were analyzed.

Results

The results showed that 7874, 13,392, 13,169, and 19,026 differentially expressed genes were significantly enriched in the glycolysis/gluconeogenesis pathway, amino acid metabolism, nitrogen metabolism, plant hormone signal transduction, and other related metabolic pathways in the oat roots at 2, 4, 8, and 12 h after inoculation with a DGL1 suspension. The GO and KEGG enrichment analyses revealed that the genes encoding plasma membrane ATPase, phosphoglycerate kinase gene PGK, ammonium transporter protein gene AMT, cellulose synthase gene CSLF6, and growth hormone response family gene IAA18 were significantly upregulated.

Discussion

It is hypothesized that the pro-growth mechanism of strain DGL1 in oats is the result of the coordination of multiple pathways through the promotion of oat energy metabolism, phytohormone signaling, secondary metabolite synthesis, and amino acid metabolism.

Whole genome analysis of Bacillus velezensis 160, biological control agent of corn head smut

Corn head smut is a disease caused by the fungus Sporisorium reilianum. This phytosanitary problem has existed for several decades in the Mezquital Valley, an important corn-producing area in central Mexico. To combat the problem, a strain identified as Bacillus subtilis 160 was applied in the field, where it decreased disease incidence and increased crop productivity. In this study, the sequencing and analysis of the whole genome sequence of this strain were carried out to identify its genetic determinants for the production of antimicrobials. The B. subtilis 160 strain was found to be Bacillus velezensis. Its genome has a size of 4,297,348 bp, a GC content of 45.8%, and 4,174 coding sequences. Comparative analysis with the genomes of four other B. velezensis strains showed that they share 2,804 genes and clusters for the production of difficidin, bacillibactin, bacilysin, macrolantin, bacillaene, fengycin, butirosin A, locillomycin, and surfactin. For the latter metabolite, unlike the other strains that have only one cluster, B. velezensis 160 has three. A cluster for synthesizing laterocidine, an antimicrobial reported only in Brevibacillus laterosporus, was also identified.

IMPORTANCE

In this study, we performed sequencing and analysis of the complete genome of the strain initially identified as Bacillus subtilis 160 as part of its characterization. This bacterium has shown its ability to control corn head smut in the field, a disease caused by the basidiomycete fungus Sporisorium reilianum. Analyzing the complete genome sequence not only provides a more precise taxonomic identification but also sheds light on the genetic potential of this bacterium, especially regarding mechanisms that allow it to exert biological control. Employing molecular and bioinformatics tools in studying the genomes of agriculturally significant microorganisms offers insights into the development of biofungicides and bioinoculants. These innovations aim to enhance plant growth and pave the way for strategies that boost crop productivity.

The AT-hook protein AHL29 promotes Bacillus subtilis colonization by suppressing SWEET2-mediated sugar retrieval in Arabidopsis roots

Beneficial Bacillus subtilis (BS) symbiosis could combat root pathogenesis, but it relies on root-secreted sugars. Understanding the molecular control of sugar flux during colonization would benefit biocontrol applications. The SWEET (Sugar Will Eventually Be Exported Transporter) uniporter regulates microbe-induced sugar secretion from roots; thus, its homologs may modulate sugar distribution upon BS colonization. Quantitative polymerase chain reaction revealed that gene transcripts of SWEET2, but not SWEET16 and 17, were significantly induced in seedling roots after 12 h of BS inoculation. Particularly, SWEET2-β-glucuronidase fusion proteins accumulated in the apical mature zone where BS abundantly colonized. Yet, enhanced BS colonization in sweet2 mutant roots suggested a specific role for SWEET2 to constrain BS propagation, probably by limiting hexose secretion. By employing yeast one-hybrid screening and ectopic expression in Arabidopsis protoplasts, the transcription factor AHL29 was identified to function as a repressor of SWEET2 expression through the AT-hook motif. Repression occurred despite immunity signals. Additionally, enhanced SWEET2 expression and reduced colonies were specifically detected in roots of BS-colonized ahl29 mutant. Taken together, we propose that BS colonization may activate repression of AHL29 on SWEET2 transcription that would be enhanced by immunity signals, thereby maintaining adequate sugar secretion for a beneficial Bacillus association.

Endophytic Bacillus vallismortis and Bacillus tequilensis bacteria isolated from medicinal plants enhance phosphorus acquisition and fortify Brassica napus L. vegetative growth and metabolic content

Phosphorus fertilization imposes critical limitations on crop productivity and soil health. The aim of the present work is to explore the potential of two phosphate solubilizing bacteria (PSB) species in phosphorus supplementation of canola (Brassica napus L.). Out of 38 bacterial isolates obtained from nine medicinal plants, two bacterial strains (20P and 28P) were proved as the most potent for the in-vitro tricalcium phosphate solubilization test. These isolates verified their activity toward different enzymes as nitrogenase and alkaline phosphatase. Also, 20P and 28P gave a high amount of indole-3-acetic acid, 34.16 μg/ml and 35.20 μg/ml, respectively, and were positive for siderophores production as they detected moderate affinity for iron chelation. Molecular identification confirmed that strain 20P was Bacillus vallismortis and strain 28P was Bacillus tequilensis. A pot experiment was conducted to study the effect of four different phosphorus concentrations (0%, 50%, 75%, and 100% P) each alone and/or in combination with B. vallismortis, B. tequilensis, or both bacterial isolates on the vegetative growth and some physiological parameters of canola. The combined treatment of 50% phosphorus + (B. vallismortis + B. tequilensis) was generally the most effective with respect to shoot height, shoot dry mass, leaf area, photosynthetic pigment fractions, total sugar content, and accumulated NPK content. In contrast, the rhizosphere pH reached the minimum value under the same treatment. These findings highlighted the potential use of PSB (B. vallismortis and B. tequilensis) along with phosphorus fertilization as a safe sustainable tactic.

Comprehensive genomic analysis of Bacillus subtilis and Bacillus paralicheniformis associated with the pearl millet panicle reveals their antimicrobial potential against important plant pathogens

BACKGROUND

Plant microbiome confers versatile functional roles to enhance survival fitness as well as productivity. In the present study two pearl millet panicle microbiome member species Bacillus subtilis PBs 12 and Bacillus paralicheniformis PBl 36 found to have beneficial traits including plant growth promotion and broad-spectrum antifungal activity towards taxonomically diverse plant pathogens. Understanding the genomes will assist in devising a bioformulation for crop protection while exploiting their beneficial functional roles.

RESULTS

Two potential firmicute species were isolated from pearl millet panicles. Morphological, biochemical, and molecular characterization revealed their identities as Bacillus subtilis PBs 12 and Bacillus paralicheniformis PBl 36. The seed priming assays revealed the ability of both species to enhance plant growth promotion and seedling vigour index. Invitro assays with PBs 12 and PBl 36 showed the antibiosis effect against taxonomically diverse plant pathogens (Magnaporthe grisea; Sclerotium rolfsii; Fusarium solani; Alternaria alternata; Ganoderma sp.) of crops and multipurpose tree species. The whole genome sequence analysis was performed to unveil the genetic potential of these bacteria for plant protection. The complete genomes of PBs 12 and PBl 36 consist of a single circular chromosome with a size of 4.02 and 4.33 Mb and 4,171 and 4,606 genes, with a G + C content of 43.68 and 45.83%, respectively. Comparative Average Nucleotide Identity (ANI) analysis revealed a close similarity of PBs 12 and PBl 36 with other beneficial strains of B. subtilis and B. paralicheniformis and found distant from B. altitudinis, B. amyloliquefaciens, and B. thuringiensis. Functional annotation revealed a majority of pathway classes of PBs 12 (30) and PBl 36 (29) involved in the biosynthesis of secondary metabolites, polyketides, and non-ribosomal peptides, followed by xenobiotic biodegradation and metabolism (21). Furthermore, 14 genomic regions of PBs 12 and 15 of PBl 36 associated with the synthesis of RiPP (Ribosomally synthesized and post-translationally modified peptides), terpenes, cyclic dipeptides (CDPs), type III polyketide synthases (T3PKSs), sactipeptides, lanthipeptides, siderophores, NRPS (Non-Ribosomal Peptide Synthetase), NRP-metallophone, etc. It was discovered that these areas contain between 25,458 and 33,000 secondary metabolite-coding MiBiG clusters which code for a wide range of products, such as antibiotics. The PCR-based screening for the presence of antimicrobial peptide (cyclic lipopeptide) genes in PBs 12 and 36 confirmed their broad-spectrum antifungal potential with the presence of spoVG, bacA, and srfAA AMP genes, which encode antimicrobial compounds such as subtilin, bacylisin, and surfactin.

CONCLUSION

The combined in vitro studies and genome analysis highlighted the antifungal potential of pearl millet panicle-associated Bacillus subtilis PBs12 and Bacillus paralicheniformis PBl36. The genetic ability to synthesize several antimicrobial compounds indicated the industrial value of PBs 12 and PBl 36, which shed light on further studies to establish their action as a biostimulant for crop protection.

Evaluation of the control efficacy of antagonistic bacteria from V-Ti magnetite mine tailings on kiwifruit brown spots in pot and field experiments

Seemingly barren heavy-metal-polluted vanadium (V) and titanium (Ti) magnetite mine tailings contain various functional microbes, yet it is unclear whether this includes microbial resources relevant to the biological control of plant diseases. Kiwifruit brown leaf spot disease, caused by Corynespora cassiicola, can seriously reduce kiwifruit yield. To discover effective control measures for kiwifruit leaf spot, 18 bacteria strains among 136 tailing-isolated bacteria from V-Ti magnetite mine tailings were identified as inhibiting C. cassiicola by the confrontation plate method, indicating that antagonistic bacteria surviving in the V-Ti magnetite mine tailings were present at a low level. The 18 antagonistic strains could be divided into two BOX-A1R clusters. The 13 representative strains that were selected for phylogenetic tree construction based on their 16S rRNA sequences belonged to the Bacillus genus. Five predominant strains exhibited different toxin-production times and intensities, with four of them initiating toxin production at 32 h. Among them, Bacillus sp. KT-10 displayed the highest bacteriostatic rate (100%), with a 37.5% growth inhibition rate and an antagonistic band of 3.2 cm against C. cassiicola. Bacillus sp. KT10 also showed a significant inhibitory effect against the expansion speed of kiwifruit brown spots in the pot. The relative control effect was 78.48 and 83.89% at 7 days after the first and last spraying of KT-10 dilution, respectively, confirming a good effect of KT-10 on kiwifruit brown leaf spots in the field. This study demonstrated for the first time that there are some antagonistic bacteria to pathogenic C. cassiicola in V-Ti magnetite mine tailings, and Bacillus sp. KT10 was found to have a good control effect on kiwifruit brown leaf spots in pots and fields, which provided an effective biological control measurement for kiwifruit brown leaf spots.

A scientific version of understanding "Why did the chickens cross the road"? - A guided journey through Bacillus spp. towards sustainable agriculture, circular economy and biofortification

The world, a famished planet with an overgrowing population, requires enormous food crops. This scenario compelled the farmers to use a high quantity of synthetic fertilizers for high food crop productivity. However, prolonged usage of chemical fertilizers results in severe adverse effects on soil and water quality. On the other hand, the growing population significantly consumes large quantities of poultry meats. Eventually, this produces a mammoth amount of poultry waste, chicken feathers. Owing to the protein value of the chicken feathers, these wastes are converted into protein hydrolysate and further extend their application as biostimulants for sustained agriculture. The protein profile of chicken feather protein hydrolysate (CFPH) produced through Bacillus spp. was the maximum compared to physical and chemical protein extraction methods. Several studies proved that the application of CFPH and active Bacillus spp. culture to soil and plants results in enhanced plant growth, phytochemical constituents, crop yield, soil nutrients, fertility, microbiome and resistance against diverse abiotic and biotic stresses. Overall, "CFPH - Jack of all trades" and "Bacillus spp. - an active camouflage to the surroundings where they applied showed profound and significant benefits to the plant growth under the most adverse conditions. In addition, Bacillus spp. coheres the biofortification process in plants through the breakdown of metals into metal ions that eventually increase the nutrient value of the food crops. However, detailed information on them is missing. This can be overcome by further real-world studies on rhizoengineering through a multi-omics approach and their interaction with plants. This review has explored the best possible and efficient strategy for managing chicken feather wastes into protein-rich CFPH through Bacillus spp. bioconversion and utilizing the CFPH and Bacillus spp. as biostimulants, biofertilizers, biopesticides and biofortificants. This paper is an excellent report on organic waste management, circular economy and sustainable agriculture research frontier.

Bacillus species as tools for biocontrol of plant diseases: A meta-analysis of twenty-two years of research, 2000-2021

The traditional way of dealing with plant diseases has been the use of chemical products, but these harm the environment and are incompatible with the global effort for sustainable development. The use of Bacillus and related species in the biological control of plant diseases is a trend in green agriculture. Many studies report the positive effect of these bacteria, but a synthesis is still necessary. So, the objective of this work is to perform a meta-analysis of Bacillus biocontrol potential and identify factors that drive its efficacy. Data were compiled from articles published in journals listed in two of the main scientific databases between 2000 and 2021. Among 6159 articles retrieved, 399 research papers met the inclusion criteria for a systematic review. Overall, Bacilli biocontrol agents reduced disease by 60% compared to control groups. Furthermore, experimental tests with higher concentrations show a strong protective effect, unlike low and single concentration essays. Biocontrol efficacy also increased when used as a protective inoculation rather than therapeutic inoculation. Inoculation directly in the fruit has a greater effect than soil drenching. The size of the effect of Bacillus-based commercial products is lower than the newly tested strains. The findings presented in this study confirm the power of Bacillus-based bioinoculants and provide valuable guidance for practitioners, researchers, and policymakers seeking effective and sustainable solutions in plant disease management.

Bacillus-based biocontrol beyond chemical control in central Africa: the challenge of turning myth into reality

Agricultural productivity in the Great Lakes Countries of Central Africa, including Burundi, Rwanda, and the Democratic Republic of Congo, is affected by a wide range of diseases and pests which are mainly controlled by chemical pesticides. However, more than 30% of the pesticides used in the region are banned in European Union due to their high toxicity. Globally available safe and eco-friendly biological alternatives to chemicals are virtually non-existent in the region. Bacillus PGPR-based biocontrol products are the most dominant in the market and have proven their efficacy in controlling major plant diseases reported in the region. With this review, we present the current situation of disease and pest management and urge the need to utilize Bacillus-based control as a possible sustainable alternative to chemical pesticides. A repertoire of strains from the Bacillus subtilis group that have shown great potential to antagonize local pathogens is provided, and efforts to promote their use, as well as the search for indigenous and more adapted Bacillus strains to local agro-ecological conditions, should be undertaken to make sustainable agriculture a reality in the region.

Antimicrobial profile of the culturable olive sporobiota and its potential as a source of biocontrol agents for major phytopathogens in olive agriculture

BACKGROUND

The phytopathogens Xylella fastidiosa and Verticillium dahliae present an unparalleled threat to olive agriculture. However, there is no efficient field treatment available today for either pest. Spore-forming bacteria (i.e., the sporobiota) are known for their extraordinary resistance properties and antimicrobial activity. The aim of this study was thus to identify potential novel sustainable spore-forming biocontrol agents derived from the culturable olive microbiome, termed the sporobiota, in general and in particular against X. fastidiosa and V. dahliae.

RESULTS

We demonstrate the wide-ranging antimicrobial profile of 415 isolates from the culturable olive sporobiota towards human and plant pathogens. We further identified five candidates with antagonistic activity against X. fastidiosa and V. dahliae. These belong to the Bacillus subtilis, Bacillus cereus and Peribacillus simplex clade. The activity was related to the species and their relative origin (soil versus leaf endophytic). It is of particular interest that two of these candidates are already naturally present at the site of disease-development that is, plant interior. We further confirmed the presence of lipopeptide genes potentially associated with the reported bioactivity.

CONCLUSIONS

The study provides insights into how members of the olive sporobiota may support the olive plant to ward off detrimental pathogens. It further yields five promising candidates for the development of eco-friendly, multi-active biocontrol agents in olive agriculture. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Recent advances in Bacillus-mediated plant growth enhancement: a paradigm shift in redefining crop resilience

The Bacillus genus has emerged as an important player in modern agriculture, revolutionizing plant growth promotion through recent advances. This review provides a comprehensive overview of the critical role Bacillus species play in boosting plant growth and agricultural sustainability. Bacillus genus bacteria benefit plants in a variety of ways, according to new research. Nitrogen fixation, phosphate solubilization, siderophore production, and the production of growth hormones are examples of these. Bacillus species are also well-known for their ability to act as biocontrol agents, reducing phytopathogens and protecting plants from disease. Molecular biology advances have increased our understanding of the complex interplay between Bacillus species and plants, shedding light on the genetic and metabolic underpinnings of these interactions. Furthermore, novel biotechnology techniques have enabled the development of Bacillus-based biofertilizers and biopesticides, providing sustainable alternatives to conventional chemical inputs. Apart from this, the combination of biochar and Bacillus species in current biotechnology is critical for improving soil fertility and encouraging sustainable agriculture through enhanced nutrient retention and plant growth. This review also emphasizes the Bacillus genus bacteria's ability to alleviate environmental abiotic stresses such as drought and salinity, hence contributing to climate-resilient agriculture. Moreover, the authors discuss the challenges and prospects associated with the practical application of Bacillus-based solutions in the field. Finally, recent advances in Bacillus-mediated plant growth promotion highlight their critical significance in sustainable agriculture. Understanding these improvements is critical for realizing the full potential of Bacillus genus microorganisms to address current global food production concerns.

The silicon regulates microbiome diversity and plant defenses during cold stress in Glycine max L

Introduction

With climate change, frequent exposure of bioenergy and food crops, specifically soybean (Glycine max L.), to low-temperature episodes is a major obstacle in maintaining sustainable plant growth at early growth stages. Silicon (Si) is a quasi-essential nutrient that can help to improve stress tolerance; however, how Si and a combination of cold stress episodes influence plant growth, plant physiology, and microbiome diversity has yet to be fully discovered.

Methods

The soybean plants were exposed to cold stress (8-10°C) with or without applying Si, and the different plant organs (shoot and root) and rhizospheric soil were subjected to microbiome analysis. The plant growth, physiology, and gene expression analysis of plant defenses during stress and Si were investigated.

Results and discussion

We showed that cold stress significantly retarded soybean plants' growth and biomass, whereas, Si-treated plants showed ameliorated negative impacts on plant growth at early seedling stages. The beneficial effects of Si were also evident from significantly reduced antioxidant activities - suggesting lower cold-induced oxidative stress. Interestingly, Si also downregulated critical genes of the abscisic acid pathway and osmotic regulation (9-cis-epoxy carotenoid dioxygenase and dehydration-responsive element binding protein) during cold stress. Si positively influenced alpha and beta diversities of bacterial and fungal microbiomes with or without cold stress. Results showed significant variation in microbiome composition in the rhizosphere (root and soil) and phyllosphere (shoot) in Si-treated plants with or without cold stress exposures. Among microbiome phyla, Proteobacteria, Bacteroidota, and Ascomycota were significantly more abundant in Si treatments in cold stress than in control conditions. For the core microbiome, we identified 179 taxa, including 88 unique bacterial genera in which Edaphobacter, Haliangium, and Streptomyces were highly abundant. Enhanced extracellular enzyme activities in the cold and Si+cold treatments, specifically phosphatase and glucosidases, also reflected the microbiome abundance. In conclusion, this work elucidates cold-mediated changes in microbiome diversity and plant growth, including the positive impact Si can have on cold tolerance at early soybean growth stages - a step toward understanding crop productivity and stress tolerance.

Characterization and evaluation of Bacillus subtilis GYUN-2311 as a biocontrol agent against Colletotrichum spp. on apple and hot pepper in Korea

Crop plants are vulnerable to a variety of diseases, including anthracnose, caused by various species of Colletotrichum fungi that damages major crops, including apples and hot peppers. The use of chemical fungicides for pathogen control may lead to environmental pollution and disease resistance. Therefore, we conducted this research to develop a Bacillus subtilis-based biological control agent (BCA). B. subtilis GYUN-2311 (GYUN-2311), isolated from the rhizosphere soil of an apple orchard, exhibited antagonistic activity against a total of 12 fungal pathogens, including eight Colletotrichum species. The volatile organic compounds (VOCs) and culture filtrate (CF) from GYUN-2311 displayed antifungal activity against all 12 pathogens, with 81% control efficiency against Fusarium oxysporum for VOCs and 81.4% control efficacy against Botryosphaeria dothidea for CF. CF also inhibited germination and appressorium formation in Colletotrichum siamense and C. acutatum. The CF from GYUN-2311 showed antifungal activity against all 12 pathogens in different media, particularly in LB medium. It also exhibited plant growth-promoting (PGP) activity, lytic enzyme activity, siderophore production, and the ability to solubilize insoluble phosphate. In trials on apples and hot peppers, GYUN-2311 effectively controlled disease, with 75 and 70% control efficacies against C. siamense in wounded and unwounded apples, respectively. Similarly, the control efficacy of hot pepper against C. acutatum in wounded inoculation was 72%. Combined application of GYUN-2311 and chemical suppressed hot pepper anthracnose to a larger extent than other treatments, such as chemical control, pyraclostrobin, TK®, GYUN-2311 and cross-spraying of chemical and GYUN-2311 under field conditions. The genome analysis of GYUN-2311 identified a circular chromosome comprising 4,043 predicted protein-coding sequences (CDSs) and 4,096,969 bp. B. subtilis SRCM104005 was the strain with the highest average nucleotide identity (ANI) to GYUN-2311. AntiSMASH analysis identified secondary metabolite biosynthetic genes, such as subtilomycin, bacillaene, fengycin, bacillibactin, pulcherriminic acid, subtilosin A, and bacilysin, whereas BAGEL analysis confirmed the presence of competence (ComX). Six secondary metabolite biosynthetic genes were induced during dual culture in the presence of C. siamense. These findings demonstrate the biological control potential of GYUN-2311 against apple and hot pepper anthracnose.

Enhancing Water Status and Nutrient Uptake in Drought-Stressed Lettuce Plants (Lactuca sativa L.) via Inoculation with Different Bacillus spp. Isolated from the Atacama Desert

Drought is a major challenge for agriculture worldwide, being one of the main causes of losses in plant production. Various studies reported that some soil's bacteria can improve plant tolerance to environmental stresses by the enhancement of water and nutrient uptake by plants. The Atacama Desert in Chile, the driest place on earth, harbors a largely unexplored microbial richness. This study aimed to evaluate the ability of various Bacillus sp. from the hyper arid Atacama Desert in the improvement in tolerance to drought stress in lettuce (Lactuca sativa L. var. capitata, cv. "Super Milanesa") plants. Seven strains of Bacillus spp. were isolated from the rhizosphere of the Chilean endemic plants Metharme lanata and Nolana jaffuelii, and then identified using the 16s rRNA gene. Indole acetic acid (IAA) production, phosphate solubilization, nitrogen fixation, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity were assessed. Lettuce plants were inoculated with Bacillus spp. strains and subjected to two different irrigation conditions (95% and 45% of field capacity) and their biomass, net photosynthesis, relative water content, photosynthetic pigments, nitrogen and phosphorus uptake, oxidative damage, proline production, and phenolic compounds were evaluated. The results indicated that plants inoculated with B. atrophaeus, B. ginsengihumi, and B. tequilensis demonstrated the highest growth under drought conditions compared to non-inoculated plants. Treatments increased biomass production and were strongly associated with enhanced N-uptake, water status, chlorophyll content, and photosynthetic activity. Our results show that specific Bacillus species from the Atacama Desert enhance drought stress tolerance in lettuce plants by promoting several beneficial plant traits that facilitate water absorption and nutrient uptake, which support the use of this unexplored and unexploited natural resource as potent bioinoculants to improve plant production under increasing drought conditions.

Impacts of UV radiation on Bacillus biocontrol agents and their resistance mechanisms

Bacillus biocontrol agent(s) BCA(s) such as Bacillus cereus, Bacillus thuringiensis and Bacillus subtilis have been widely applied to control insects' pests of plants and pathogenic microbes, improve plant growth, and facilitate their resistance to environmental stresses. In the last decade, researchers have shown that, the application of Bacillus biocontrol agent(s) BCA(s) optimized agricultural production yield, and reduced disease risks in some crops. However, these bacteria encountered various abiotic stresses, among which ultraviolet (UV) radiation severely decrease their efficiency. Researchers have identified several strategies by which Bacillus biocontrol agents resist the negative effects of UV radiation, including transcriptional response, UV mutagenesis, biochemical and artificial means (addition of protective agents). These strategies are governed by distinct pathways, triggered by UV radiation. Herein, the impact of UV radiation on Bacillus biocontrol agent(s) BCA(s) and their mechanisms of resistance were discussed.

Cellulose-degrading bacteria improve conversion efficiency in the co-digestion of dairy and chicken manure by black soldier fly larvae

Black soldier fly larvae (BSFL) have potential utility in converting livestock manure into larval biomass as a protein source for livestock feed. However, BSFL have limited ability to convert dairy manure (DM) rich in lignocellulose. Our previous research demonstrated that feeding BSFL with mixtures of 40% dairy manure and 60% chicken manure (DM40) provides a novel strategy for significantly improving their efficiency in converting DM. However, the mechanisms underlying the efficient conversion of DM40 by BSFL are unclear. In this study, we conducted a holistic study on the taxonomic stucture and potential functions of microbiota in the larval gut and manure during the DM and DM40 conversion by BSFL, as well as the effects of BSFL on cellulosic biodegradation and biomass production. Results showed that BSFL can consume cellulose and other nutrients more effectively and harvest more biomass in a shorter conversion cycle in the DM40 system. The larval gut in the DM40 system yielded a higher microbiota complexity. Bacillus and Amphibacillus in the BSFL gut were strongly correlated with the larval cellulose degradation capacity. Furthermore, in vitro screening results for culturable cellulolytic microbes from the larval guts showed that the DM40 system isolated more cellulolytic microbes. A key bacterial strain (DM40L-LB110; Bacillus subtilis) with high cellulase activity from the larval gut of DM40 was validated for potential industrial applications. Therefore, mixing an appropriate proportion of chicken manure into DM increased the abundance of intestinal bacteria (Bacillus and Amphibacillus) producing cellulase and improved the digestion ability (particularly cellulose degradation) of BSFL to cellulose-rich manure through changes in microbial communities composition in intestine. This study reveals the microecological mechanisms underlying the high-efficiency conversion of cellulose-rich manure by BSFL and provide potential applications for the large-scale cellulose-rich wastes conversion by intestinal microbes combined with BSFL.

Identification of bioactive compounds of Bacillus velezensis HNA3 that contribute to its dual effects as plant growth promoter and biocontrol against post-harvested fungi

IMPORTANCE

The current study is an extension to our previous work on the plant growth-promoting rhizobacteria (PGPR) Bacillus velezensis HNA3 strain, which comes to confirm and reveals the huge stock of active secondary metabolites produced by HNA3. HNA3-emitted volatile organic compounds (VOCs) have demonstrated the capacity to impede the growth of phytopathogens affecting some fruits and vegetables, even in the absence of direct contact. Additionally, these volatiles enhanced soybean seed germination by breaking seed dormancy and inducing root system development. Furthermore, they promoted seedling growth, giving it prominence in soybean cultivation. The relevance of active volatiles derives from the fact that they can be developed as natural-safe biocontrol agents and plant promoters. This research validates the remarkable bioactivities exhibited by the Bacillus velezensis HNA3 and their potential applications in agriculture as an inoculant, encompassing biocontrol, plant growth promotion, and seed germination activities, thereby offering a safer alternative to hazardous chemicals.

Screening and characterization of biocontrol bacteria isolated from Ageratum conyzoides against Collectotrichum fructicola causing Chinese plum (Prunus salicina Lindl.) anthracnose

Chinese plum (Prunus salicina Lindl.) is a nutritionally and economically important stone fruit widely grown around the world. Anthracnose, caused by Collectotrichum spp., is one of the primary biotic stress factors limiting plum production. Medicinal plants may harbor rhizospheric or endophytic microorganisms that produce bioactive metabolites that can be used as anthracnose biocontrol agents. Here, 27 bacterial isolates from the medicinal plant A. conyzoides with diverse antagonistic activities against C. fructicola were screened. Based on morphological, physiological, biochemical, and molecular characterization, 25 of these isolates belong to different species of genus Bacillus, one to Pseudomonas monsensis, and one more to Microbacterium phyllosphaerae. Eight representative strains showed high biocontrol efficacy against plum anthracnose in a pot experiment. In addition, several Bacillus isolates showed a broad spectrum of inhibitory activity against a variety of fungal phytopathogens. Analysis of the volatile organic compound profile of these eight representative strains revealed a total of 47 compounds, most of which were ketones, while the others included alkanes, alkenes, alcohols, pyrazines, and phenols. Overall, this study confirmed the potential value of eight bacterial isolates for development as anthracnose biocontrol agents.

Multi-Generation Ecosystem Selection of Rhizosphere Microbial Communities Associated with Plant Genotype and Biomass in Arabidopsis thaliana

The role of the microbiome in shaping the host's phenotype has emerged as a critical area of investigation, with implications in ecology, evolution, and host health. The complex and dynamic interactions involving plants and their diverse rhizospheres' microbial communities are influenced by a multitude of factors, including but not limited to soil type, environment, and plant genotype. Understanding the impact of these factors on microbial community assembly is key to yielding host-specific and robust benefits for plants, yet it remains challenging. Here, we conducted an artificial ecosystem selection experiment for eight generations of Arabidopsis thaliana Ler and Cvi to select soil microbiomes associated with a higher or lower biomass of the host. This resulted in divergent microbial communities shaped by a complex interplay between random environmental variations, plant genotypes, and biomass selection pressures. In the initial phases of the experiment, the genotype and the biomass selection treatment had modest but significant impacts. Over time, the plant genotype and biomass treatments gained more influence, explaining ~40% of the variation in the microbial community's composition. Furthermore, a genotype-specific association of plant-growth-promoting rhizobacterial taxa, Labraceae with Ler and Rhizobiaceae with Cvi, was observed under selection for high biomass.

Influence of biofertilizer on heavy metal bioremediation and enzyme activities in the soil to revealing the potential for sustainable soil restoration

Overuse of chemical fertilizer and pesticides in agricultural activity is frequently damaging to soil health and can accumulate heavy metals in the soil environment, causing harm to plants, humans, and the ecosystem. This study was done to evaluate the effectiveness of biofertilizers in reducing heavy metal levels in contaminated soil and enhancing the activity of soil enzymes that are crucial to plant growth and development. Two bacteria strains, Pseudomonas aeruginosa. and Bacillus firmus, were chosen to develop biofertilizers based on molasses. The pot experiment was setup using a completely randomized design with four treatments and five levels; Bacillus firmus and Pseudomonas aeruginosa were used separately, and they were combined for the biofertilizer dose (20, 40, 60, 80, and 100 mL). Utilizing contaminated soils taken from a greenhouse farm the effect of biofertilizer on heavy metal bioremediation and soil enzyme activity was examined. Methods of soil agrochemical analysis were used to determine the soil physiochemical properties and the concentrations of heavy metals Cu, Fe, Zn, Cd, Mo, Mn, were determined by inductively coupled plasma-mass spectrometry ICP-MS, following DTPA extraction methods. In results, soil pH decreased from 8.28 to 7.39, Ec increased from 0.91 to 1.12, organic matter increased from 18.88 to 20.63 g/kg, N increased gradually from 16.7 to 24.4 mg/kg, and K increased from 145.25 to 201.4 mg/kg. The effect of biofertilizer treatment on soil physiochemical characteristics was significantly positive. Application of biofertilizer significantly increased the heavy metal bioavailability and the activities of soil enzymes. Soil pH were positively correlated with soil Zn (0.99819*), APK (0.95869*) activity and negatively correlated with Fe (0.96759*) also statistically significant at (p < 0.05). The soil Cu positively correlated with Fe (0.99645*), Cd (0.97866*), β.D.GLU (0.99769*) and negatively correlated with PAK (- 0.9624*). Soil ARY had positive correlation with soil Mn (0.99683*), Cd (0.95695*), and negative correlation with PAK (- 0.99424*) at (p < 0.05). Soil enzyme activities were negatively correlated to heavy metals at a significant level. Collectively, the study highlights the potential of biofertilizers as a sustainable and effective approach to enhance soil health and remediate heavy metal-contaminated soils in greenhouses.

A Novel Subcluster of Closely Related Bacillus Phages with Distinct Tail Fiber/Lysin Gene Combinations

Bacteriophages (phages) are the most numerous entities on Earth, but we have only scratched the surface of describing phage diversity. We isolated seven Bacillus subtilis phages from desert soil in the southwest United States and then sequenced and characterized their genomes. Comparative analyses revealed high nucleotide and amino acid similarity between these seven phages, which constitute a novel subcluster. Interestingly, the tail fiber and lysin genes of these phages seem to come from different origins and carry out slightly different functions. These genes were likely acquired by this subcluster of phages via horizontal gene transfer. In conjunction with host range assays, our data suggest that these phages are adapting to hosts with different cell walls.

Endophytic bacterial communities in ungerminated and germinated seeds of commercial vegetables

Chile is a prominent seed exporter globally, but the seed microbiome of vegetables (46% of seeds) and its role in the early stages of plant growth have remained largely unexplored. Here, we employed DNA metabarcoding analysis to investigate the composition and putative functions of endophytic bacterial communities in ungerminated and germinated seeds of the commercial vegetables Apiaceae (parsley and carrot), Asteraceae (lettuce), Brassicaceae (cabbage and broccoli), and Solanaceae (tomato). Bacterial quantification showed 104 to 108 copies of the 16S rRNA gene per gram of ungerminated and germinated seeds. Alpha diversity analysis (e.g., Chao1, Shannon, and Simpson indices) did not indicate significant differences (Kruskal-Wallis test) between ungerminated and germinated seeds, except for Solanaceae. However, beta diversity (PCoA) analysis showed distinctions (Adonis test) between ungerminated and germinated seeds, except Apiaceae. Pseudomonadota and Bacillota were identified as the dominant and specialist taxa in both ungerminated and germinated seed samples. Chemoheterotrophy and fermentation were predicted as the main microbial functional groups in the endophytic bacterial community. Notably, a considerable number of the 143 isolated endophytic strains displayed plant growth-promoting traits (10 to 64%) and biocontrol activity (74% to 82%) against plant pathogens (Xanthomonas and Pseudomonas). This study revealed the high variability in the abundance, diversity, composition, and functionality of endophytic bacteria between ungerminated and germinated seeds in globally commercialized vegetables. Furthermore, potential beneficial endophytic bacteria contained in their seed microbiomes that may contribute to the microbiome of the early stages, development, growth and progeny of vegetables were found.

Plant growth promoting rhizobacterium Bacillus sp. BSE01 alleviates salt toxicity in chickpea (Cicer arietinum L.) by conserving ionic, osmotic, redox and hormonal homeostasis

Soil salinity leading to sodium toxicity is developing into a massive challenge for agricultural productivity globally, inducing osmotic, ionic, and redox imbalances in plants. Considering the predicted increase in salinization risk with the ongoing climate change, applying plant growth-promoting rhizobacteria (PGPR) is an environmentally safe method for augmenting plant salinity tolerance. The present study examined the role of halotolerant Bacillus sp. BSE01 as a promising biostimulant for improving salt stress endurance in chickpea. Application of PGPR significantly increased the plant height, relative water content, and chlorophyll content of chickpea under both non-stressed and salt stress conditions. The PGPR-mediated tolerance towards salt stress was accomplished by the modulation of hormonal signaling and conservation of cellular ionic, osmotic, redox homeostasis. With salinity stress, the PGPR-treated plants significantly increased the indole-3-acetic acid and gibberellic acid contents more than the non-treated plants. Furthermore, the PGPR-inoculated plants maintained lower 1-aminocyclopropane-1-carboxylic acid and abscisic acid contents under salt treatment. The PGPR-inoculated chickpea plants also exhibited a decreased NADPH oxidase activity with reduced production of reactive oxygen species compared to the non-inoculated plants. Additionally, PGPR treatment led to increased antioxidant enzyme activities in chickpea under saline conditions, facilitating the reactive nitrogen and oxygen species detoxification, thereby limiting the nitro-oxidative damage. Following salinity stress, enhanced K+ /Na+ ratio and proline content were noted in the PGPR-inoculated chickpea plants. Therefore, Bacillus sp. BSE01, being an effective PGPR and salinity stress reducer, can further be considered to develop a bioinoculant for sustainable chickpea production under saline environments.

Bacillus velezensis BVE7 as a promising agent for biocontrol of soybean root rot caused by Fusarium oxysporum

Introduction

Soybean root rot (SRR), caused by Fusarium oxysporum, is a severe soil-borne disease in soybean production worldwide, which adversely impacts the yield and quality of soybean. The most effective method for managing crop soil-borne diseases and decreasing reliance on chemical fungicides, such as Bacillus spp., is via microbial biocontrol agents.

Methods and Results

In this study, a soil-isolated strain BVE7 was identified as B. velezensis, exhibiting broad-spectrum activity against various pathogens causing soybean root rot. BVE7 sterile filtrate, at a concentration of 10%, demonstrated significant antifungal activity by inhibiting the conidial germination, production, and mycelial growth of F. oxysporum by 61.11%, 73.44%, and 85.42%, respectively, causing hyphal malformations. The antifungal compound produced by BVE7 demonstrated adaptability to a standard environment. The pot experiment showed that BVE7 suspension could effectively control soybean root rot, with the highest control efficiency of 75.13%. Furthermore, it considerably enhanced the activity of catalase, phenylalanine ammonia lyase, superoxide dismutase, and peroxidase in soybean roots, while also preventing an increase in malondialdehyde activity. By improving the host resistance towards pathogens, the damage caused by fungi and the severity of soybean root rot have been reduced.

Discussion

This study presents the innovative utilization of B. velezensis, isolated from soybean roots in cold conditions, for effectively controlling soybean root rot caused by F. oxysporum. The findings highlight the remarkable regional and adaptive characteristics of this strain, making it an excellent candidate for combating soybean root rot in diverse environments. In conclusion, B. velezensis BVE7 demonstrated potential in effectively reducing SRR incidence and can be considered as a viable option for SRR management.

Simply Versatile: The Use of Peribacillus simplex in Sustainable Agriculture

Peribacillus simplex is a Gram-positive, spore-forming bacterium derived from a vast range of different origins. Notably, it is part of the plant-growth-promoting rhizobacterial community of many crops. Although members of the Bacillaceae family have been widely used in agriculture, P. simplex has, so far, remained in the shadow of its more famous relatives, e.g., Bacillus subtilis or Bacillus thuringiensis. Recent studies have, however, started to uncover the bacterium's highly promising and versatile properties, in particular in agricultural and environmental applications. Hence, here, we review the plant-growth-promoting features of P. simplex, as well as its biocontrol activity against a variety of detrimental plant pests in different crops. We further highlight the bacterium's potential as a bioremediation agent for environmental contaminants, such as metals, pesticide residues, or (crude) oil. Finally, we examine the recent developments in the European regulatory landscape to facilitate the use of microorganisms in plant protection products. Undoubtedly, further studies on P. simplex will reveal additional benefits for agricultural and environmentally friendly applications.

Enhancement of sulfur metabolism and antioxidant machinery confers Bacillus sp. Jrh14-10-induced alkaline stress tolerance in plant

Alkaline stress is a major environmental challenge that restricts plant growth and agricultural productivity worldwide. Plant growth-promoting rhizobacteria (PGPR) can be used to effectively enhance plant abiotic stress in an environment-friendly manner. However, PGPR that can enhance alkalinity tolerance are not well-studied and the mechanisms by which they exert beneficial effects remain elusive. In this study, we isolated Jrh14-10 from the rhizosphere soil of halophyte Halerpestes cymbalaria (Pursh) Green and found that it can produce indole-3-acetic acid (IAA) and siderophore. By 16S rRNA gene sequencing, it was classified as Bacillus licheniformis. Inoculation Arabidopsis seedlings with Jrh14-10 significantly increased the total fresh weight (by 148.1%), primary root elongation (by 1121.7%), and lateral root number (by 108.8%) under alkaline stress. RNA-Seq analysis showed that 3389 genes were up-regulated by inoculation under alkaline stress and they were associated with sulfur metabolism, photosynthetic system, and oxidative stress response. Significantly, the levels of Cys and GSH were increased by 144.3% and 48.7%, respectively, in the inoculation group compared to the control under alkaline stress. Furthermore, Jrh14-10 markedly enhanced the activities of antioxidant enzymes, resulting in lower levels of O2•-, H2O2, and MDA as well as higher levels of Fv/Fm in alkaline-treated seedlings. In summary, Jrh14-10 can improve alkaline stress resistance in seedlings which was accompanied by an increase in sulfur metabolism-mediated GSH synthesis and antioxidant enzyme activities. These results provide a mechanistic understanding of the interactions between a beneficial bacterial strain and plants under alkaline stress.

Microbial Exudates as Biostimulants: Role in Plant Growth Promotion and Stress Mitigation

Microbes hold immense potential, based on the fact that they are widely acknowledged for their role in mitigating the detrimental impacts of chemical fertilizers and pesticides, which were extensively employed during the Green Revolution era. The consequence of this extensive use has been the degradation of agricultural land, soil health and fertility deterioration, and a decline in crop quality. Despite the existence of environmentally friendly and sustainable alternatives, microbial bioinoculants encounter numerous challenges in real-world agricultural settings. These challenges include harsh environmental conditions like unfavorable soil pH, temperature extremes, and nutrient imbalances, as well as stiff competition with native microbial species and host plant specificity. Moreover, obstacles spanning from large-scale production to commercialization persist. Therefore, substantial efforts are underway to identify superior solutions that can foster a sustainable and eco-conscious agricultural system. In this context, attention has shifted towards the utilization of cell-free microbial exudates as opposed to traditional microbial inoculants. Microbial exudates refer to the diverse array of cellular metabolites secreted by microbial cells. These metabolites enclose a wide range of chemical compounds, including sugars, organic acids, amino acids, peptides, siderophores, volatiles, and more. The composition and function of these compounds in exudates can vary considerably, depending on the specific microbial strains and prevailing environmental conditions. Remarkably, they possess the capability to modulate and influence various plant physiological processes, thereby inducing tolerance to both biotic and abiotic stresses. Furthermore, these exudates facilitate plant growth and aid in the remediation of environmental pollutants such as chemicals and heavy metals in agroecosystems. Much like live microbes, when applied, these exudates actively participate in the phyllosphere and rhizosphere, engaging in continuous interactions with plants and plant-associated microbes. Consequently, they play a pivotal role in reshaping the microbiome. The biostimulant properties exhibited by these exudates position them as promising biological components for fostering cleaner and more sustainable agricultural systems.

Evaluation and Genome Mining of Bacillus stercoris Isolate B.PNR1 as Potential Agent for Fusarium Wilt Control and Growth Promotion of Tomato

Recently, strategies for controlling Fusarium oxysporum f. sp. lycopersici (Fol), the causal agent of Fusarium wilt of tomato, focus on using effective biocontrol agents. In this study, an analysis of the biocontrol and plant growth promoting (PGP) attributes of 11 isolates of loamy soil Bacillus spp. has been conducted. Among them, the isolates B.PNR1 and B.PNR2 inhibited the mycelial growth of Fol by inducing abnormal fungal cell wall structures and cell wall collapse. Moreover, broad-spectrum activity against four other plant pathogenic fungi, F. oxysporum f. sp. cubense race 1 (Foc), Sclerotium rolfsii, Colletotrichum musae, and C. gloeosporioides were noted for these isolates. These two Bacillus isolates produced indole acetic acid, phosphate solubilization enzymes, and amylolytic and cellulolytic enzymes. In the pot experiment, the culture filtrate from B.PNR1 showed greater inhibition of the fungal pathogens and significantly promoted the growth of tomato plants more than those of the other treatments. Isolate B.PNR1, the best biocontrol and PGP, was identified as Bacillus stercoris by its 16S rRNA gene sequence and whole genome sequencing analysis (WGS). The WGS, through genome mining, confirmed that the B.PNR1 genome contained genes/gene cluster of a nonribosomal peptide synthetase/polyketide synthase, such as fengycin, surfactin, bacillaene, subtilosin A, bacilysin, and bacillibactin, which are involved in antagonistic and PGP activities. Therefore, our finding demonstrates the effectiveness of B. stercoris strain B.PNR1 as an antagonist and for plant growth promotion, highlighting the use of this microorganism as a biocontrol agent against the Fusarium wilt pathogen and PGP abilities in tomatoes.

Recent Advances in Microbial-Assisted Remediation of Cadmium-Contaminated Soil

Soil contamination with cadmium (Cd) is a severe concern for the developing world due to its non-biodegradability and significant potential to damage the ecosystem and associated services. Industries such as mining, manufacturing, building, etc., rapidly produce a substantial amount of Cd, posing environmental risks. Cd toxicity in crop plants decreases nutrient and water uptake and translocation, increases oxidative damage, interferes with plant metabolism and inhibits plant morphology and physiology. However, various conventional physicochemical approaches are available to remove Cd from the soil, including chemical reduction, immobilization, stabilization and electro-remediation. Nevertheless, these processes are costly and unfriendly to the environment because they require much energy, skilled labor and hazardous chemicals. In contrasting, contaminated soils can be restored by using bioremediation techniques, which use plants alone and in association with different beneficial microbes as cutting-edge approaches. This review covers the bioremediation of soils contaminated with Cd in various new ways. The bioremediation capability of bacteria and fungi alone and in combination with plants are studied and analyzed. Microbes, including bacteria, fungi and algae, are reported to have a high tolerance for metals, having a 98% bioremediation capability. The internal structure of microorganisms, their cell surface characteristics and the surrounding environmental circumstances are all discussed concerning how microbes detoxify metals. Moreover, issues affecting the effectiveness of bioremediation are explored, along with potential difficulties, solutions and prospects.

A novel biocontrol agent Bacillus velezensis K01 for management of gray mold caused by Botrytis cinerea

Gray mold is a destructive plant disease caused by a fungal pathogen Botrytis cinerea. The use of plant growth promoting rhizobacteria (PGPR) has proven to be a promising method to control this disease. Bacillus velezensis K01 was isolated from the rhizosphere of planting tomatoes. Strain K01 has a range of roles, including the ability to solubilize phytate phosphorus, stimulate resistant response, and produce indoleacetic acid (IAA), protease, cellulase, and antimicrobial substances. Strain K01 was found to inhibit 12 phytopathogenic fungi and 5 phytopathogenic bacteria. Specially, strain K01 demonstrated a biocontrol efficiency of over 78% against gray mold caused by B. cinerea on the leaves and fruits of tomato and pepper. Additionally, K01 was found to promote the growth of maize seedlings. Further genomic analysis revealed that K01 belongs to B. velezensis, which is consistent with phylogenetic analysis, average nucleotide polymorphism (ANI), and digital DNA-DNA hybridization (dDDH). The genome of strain K01 had a size of 3,927,799 bp and deduced 3866 predicted genes, with an average guanine-cytosine (GC) content of 46.5%. Based on the analyses of genomic secondary metabolites, over 18.4% of the genome was annotated to 12 gene clusters related to antimicrobial metabolite synthesis. Additionally, genome annotation and comparative genomics identified several genes associated with plant growth promotion and environmental adaption. These findings suggest that B. velezensis K01 has the potential to serve as a new biocontrol agent for management of gray mold on tomato and pepper.

MarR Family Transcriptional Regulators and Their Roles in Plant-Interacting Bacteria

The relationship between plants and associated soil microorganisms plays a major role in ecosystem functioning. Plant-bacteria interactions involve complex signaling pathways regulating various processes required by bacteria to adapt to their fluctuating environment. The establishment and maintenance of these interactions rely on the ability of the bacteria to sense and respond to biotic and abiotic environmental signals. In this context, MarR family transcriptional regulators can use these signals for transcriptional regulation, which is required to establish adapted responses. MarR-like transcriptional regulators are essential for the regulation of the specialized functions involved in plant-bacteria interactions in response to a wide range of molecules associated with the plant host. The conversion of environmental signals into changes in bacterial physiology and behavior allows the bacteria to colonize the plant and ensure a successful interaction. This review focuses on the mechanisms of plant-signal perception by MarR-like regulators, namely how they (i) allow bacteria to cope with the rhizosphere and plant endosphere, (ii) regulate the beneficial functions of Plant-Growth-Promoting Bacteria and (iii) regulate the virulence of phytopathogenic bacteria.

Molecular characterization and antifungal activity of lipopeptides produced from Bacillus subtilis against plant fungal pathogen Alternaria alternata

Over 380 host plant species have been known to develop leaf spots as a result of the fungus Alternaria alternata. It is an aspiring pathogen that affects a variety of hosts and causes rots, blights, and leaf spots on different plant sections. In this investigation, the lipopeptides from the B. subtilis strains T3, T4, T5, and T6 were evaluated for their antifungal activities. In the genomic DNA, iturin, surfactin, and fengycin genes were found recovered from B. subtilis bacterium by PCR amplification. From different B. subtilis strains, antifungal Lipopeptides were extracted, identified by HPLC, and quantified with values for T3 (24 g/ml), T4 (32 g/ml), T5 (28 g/ml), and T6 (18 g/ml). To test the antifungal activity, the isolated lipopeptides from the B. subtilis T3, T4, T5, and T6 strains were applied to Alternaria alternata at a concentration of 10 g/ml. Lipopeptides were found to suppress Alternaria alternata at rates of T3 (75.14%), T4 (75.93%), T5 (80.40%), and T6 (85.88%). The T6 strain outperformed the other three by having the highest antifungal activity against Alternaria alternata (85.88%).

An overview of plasmid transfer in the plant microbiome

Plant microbiomes are pivotal for healthy plant physiological development. Microbes live in complex co-association with plant hosts, and interactions within these microbial communities vary with plant genotype, plant compartment, phenological stage, and soil properties, among others. Plant microbiomes also harbor a substantial and diverse pool of mobile genes encoded on plasmids. Several plasmid functions attributed to plant-associated bacteria are relatively poorly understood. Additionally, the role of plasmids in disseminating genetic traits within plant compartments is not well known. Here, we present the current knowledge on the occurrence, diversity, function, and transfer of plasmids in plant microbiomes, emphasizing the factors that could modulate gene transfer in-planta. We also describe the role of the plant microbiome as a plasmid reservoir and the dissemination of its genetic material. We include a brief discussion on the current methodological limitations in studying plasmid transfer within plant microbiomes. This information could be useful to elucidate the dynamics of the bacterial gene pools, the adaptations different organisms have made, and variations in bacterial populations that might have never been described before, particularly in complex microbial communities associated with plants in natural and anthropogenic impacted environments.

Development of Optical Label-Free Biosensor Method in Detection of Listeria monocytogenes from Food

The present work describes an alternative method for detecting and identifying Listeria monocytogenes in food samples by developing a nanophotonic biosensor containing bioreceptors and optical transducers. The development of photonic sensors for the detection of pathogens in the food industry involves the implementation of procedures for selecting probes against the antigens of interest and the functionalization of the sensor surfaces on which the said bioreceptors are located. As a previous step to functionalizing the biosensor, an immobilization control of these antibodies on silicon nitride surfaces was carried out to check the effectiveness of in plane immobilization. On the one hand, it was observed that a Listeria monocytogenes-specific polyclonal antibody has a greater binding capacity to the antigen at a wide range of concentrations. A Listeria monocytogenes monoclonal antibody is more specific and has a greater binding capacity only at low concentrations. An assay for evaluating selected antibodies against particular antigens of Listeria monocytogenes bacteria was designed to determine the binding specificity of each probe using the indirect ELISA detection technique. In addition, a validation method was established against the reference method for many replicates belonging to different batches of meat-detectable samples, with a medium and pre-enrichment time that allowed optimal recovery of the target microorganism. Moreover, no cross-reactivity with other nontarget bacteria was observed. Thus, this system is a simple, highly sensitive, and accurate platform for L. monocytogenes detection.

Characterization of Bacillus pumilus Strains with Targeted Gene Editing for Antimicrobial Peptides and Sporulation Factor

Due to their capacity to produce antimicrobial peptides that can prevent the growth of diseases, many Bacillus spp. are beneficial to plants. In this study, we looked into the antagonistic activity of the B. pumilus 3-19 strain and its derivatives following targeted genome editing. Two peptide genes with antibacterial action, bacilysin (bac) and bacteriocin (bact), and the sigF gene, which encodes the sigma factor of sporulation, were specifically inactivated using the CRISPR-Cas9 system in the genome of B. pumilus 3-19. Antibacterial activity against B. cereus and Pantoea brenneri decreased as a result of the inactivation of target genes in the B. pumilus 3-19 genome, with a noticeable effect against bacilysin. The growth dynamics of the culture changed when the bac, bact, and sigF genes were inactivated, and the altered strains had less proteolytic activity. An asporogenic mutant of B. pumilus 3-19 was obtained by inactivating the sigF gene. It has been proven that bacilysin plays a unique part in the development of B. pumilus 3-19's antagonistic action against soil microorganisms.

Recirculating packed-bed biofilm photobioreactor combined with membrane ultrafiltration as advanced wastewater treatment

Packed-bed biofilm photobioreactor combined with ultrafiltration membrane was investigated for intensifying the process for secondary wastewater effluent treatment. Cylindrical glass carriers were used as supporting material for the microalgal-bacterial biofilm, which developed from indigenous microbial consortium. Glass carriers allowed adequate growth of the biofilm with limited suspended biomass. Stable operation was achieved after a start-up period of 1000 h, where supernatant biopolymer clusters were minimized and complete nitrification was observed. After that time, biomass productivity was 54 ± 18 mg·L^-1·day^-1. Green microalgae Tetradesmus obliquus and several strains of heterotrophic nitrification-aerobic denitrification bacteria and fungi were identified. Combined process exhibited COD, nitrogen and phosphorus removal rates of 56 ± 5%, 12 ± 2% and 20 ± 6%, respectively. Membrane fouling was mainly caused by biofilm formation, which was not effectively mitigated by air-scouring aided backwashing.

Arsenic contamination in groundwater and food chain with mitigation options in Bengal delta with special reference to Bangladesh

Bangladesh, situated in Bengal delta, is one of the worst affected countries by arsenic contamination in groundwater. Most of the people in the country are dependent on groundwater for domestic and irrigation purposes. Currently, 61 districts out of 64 districts of Bangladesh are affected by arsenic contamination. Drinking arsenic contaminated groundwater is the main pathway of arsenic exposure in the population. Additionally, the use of arsenic-contaminated groundwater for irrigation purpose in crop fields in Bangladesh has elevated arsenic concentration in surface soil and in the plants. In many arsenic-affected countries, including Bangladesh, rice is reported to be one of the significant sources of arsenic contamination. This review discussed scenario of groundwater arsenic contamination and transmission of arsenic through food chain in Bangladesh. The study further highlighted the human health perspectives of arsenic exposure in Bangladesh with possible mitigation and remediation options employed in the country.

Selenium and Bacillus proteolyticus SES synergistically enhanced ryegrass to remediate Cu-Cd-Cr contaminated soil

Heavy metal compound contaminated soil is an ecological threat, and soil containing copper (Cu), cadmium (Cd) and chromium (Cr) simultaneously is widely distributed. The application of phytoremediation in heavy metal combined contamination is still limited. In this study, to explore whether and how exogenous selenium (Se) and Bacillus proteolyticus SES enhance the remediation of combined Cu-Cd-Cr contaminated soil by ryegrass, pot experiments were carried out. Se alone or in combination with B. proteolyticus SES treatment increased the removal rates of heavy metals in the rhizosphere soil by 17.38%-157.25% relative to the control, while Se + B. proteolyticus SES treatment played a greater role in improving the heavy metals tolerance of ryegrass and increasing the activity of soil acid phosphatase. Moreover, Se and B. proteolyticus SES favored the preferential recruitment of specific taxa with the capacity of plant growth promotion and heavy metals resistance to the rhizosphere. The rhizosphere soil of Se treatment was specifically enriched with Lysobacter, Rhodanobacter, Micrococcales, Paenarthrobacter, and Adhaeribacter, while from class Bacilli to genus Bacillus enriched extensively and specifically in the rhizosphere of B. proteolyticus SES + Se treatment. Furthermore, five functional beneficial rhizosphere microbes including: Microbacterium sp., Pseudomonas extremaustralis, Bacillus amyloliquefaciens, Priestia megaterium, and Bacillus subtilis were isolated from the two treatments with the best remediation effect and synthetic communities (SynComs) were constructed. SynComs inoculation experiment further demonstrated the role of specific beneficial microbes in regulating the bioavailability of heavy metals. Results revealed that Se supplementation efficiently facilitated the phytoextraction of combined Cu-Cd-Cr contaminated soil, and B. proteolyticus SES inoculation showed the synergistical enhancement effect in the presence of Se.

Performance of Plant-Growth-Promoting Rhizobacteria (PGPR) Isolated from Sandy Soil on Growth of Tomato (Solanum lycopersicum L.)

The plant-growth-promoting rhizobacteria (PGPR) in the rhizosphere affect plant growth, health, and productivity, as well as soil-nutrient contents. They are considered a green and eco-friendly technology that will reduce chemical-fertilizer usage, thereby reducing production costs and protecting the environment. Out of 58 bacterial strains isolated in Qassim, Saudi Arabia, four strains were identified by the 16S rRNA as the Streptomyces cinereoruber strain P6-4, Priestia megaterium strain P12, Rossellomorea aquimaris strain P22-2, and Pseudomonas plecoglossicida strain P24. The plant-growth-promoting (PGP) features of the identified bacteria involving inorganic phosphate (P) solubilization, the production of indole acetic acid (IAA), and siderophore secretion were assessed in vitro. Regarding the P solubilization, the previous strains' efficacy reached 37.71%, 52.84%, 94.31%, and 64.20%, respectively. The strains produced considerable amounts of IAA (69.82, 251.70, 236.57, and 101.94 µg/mL) after 4 days of incubation at 30 °C. Furthermore, the rates of siderophore production reached 35.51, 26.37, 26.37, and 23.84 psu, respectively, in the same strains. The application of the selected strains in the presence of rock phosphate (RP) with tomato plants under greenhouse conditions was evaluated. The plant growth and P-uptake traits positively and significantly increased in response to all the bacterial treatments, except for some traits, such as plant height, number of leaves, and leaf DM at 21 DAT, compared to the negative control (rock phosphate, T2). Notably, the P. megaterium strain P12 (T4), followed by R. aquimaris strain P22-2 (T5), revealed the best values related to plant height (at 45 DAT), number of leaves per plant (at 45 DAT), root length, leaf area, leaf-P uptake, stem P uptake, and total plant P uptake compared to the rock phosphate. The first two components of the PCA (principal component analysis) represented 71.99% (PCA1 = 50.81% and PCA2 = 21.18%) of the variation at 45 DAT. Finally, the PGPR improved the vegetative-growth traits of the tomato plants through P solubilization, IAA, and siderophore production, and ameliorated the availability of nutrients. Thus, applying in PGPR in sustainable agriculture will potentially reduce production costs and protect the environment from contamination by chemical fertilizers and pesticides.

'A plant's major strength in rhizosphere': the plant growth promoting rhizobacteria

Human activities, industrialization and civilization have deteriorated the environment which eventually has led to alarming effects on plants and animals by heightened amounts of chemical pollutants and heavy metals in the environment, which create abiotic stress. Environmental conditions like drought, salinity, diminished macro-and micro-nutrients also contribute in abiotic stress, resulting in decrement of survival and growth of plants. Presence of pathogenic and competitive microorganisms, as well as pests lead to biotic stress and a plant alone can not defend itself. Thankfully, nature has rendered plant's rhizosphere with plant growth promoting rhizobacteria which maintain an allelopathic relationship with host plant to defend the plant and let it flourish in abiotic as well as biotic stress situations. This review discusses the mechanisms behind increase in plant growth via various direct and indirect traits expressed by associated microorganisms in the rhizosphere, along with their current scenario and promising future for sustainable agriculture. It also gives details of ten such bacterial species, viz. Acetobacter, Agrobacterium, Alcaligenes, Arthrobacter, Azospirillum, Azotobacter, Bacillus, Burkholderia, Enterobacter and Frankia, whose association with the host plants is famed for enhancing plant's growth and survival.

Bacillus cabrialesii subsp. cabrialesii subsp. nov. and Bacillus cabrialesii subsp. tritici subsp. nov., plant growth-promoting bacteria and biological control agents isolated from wheat (Triticum turgidum subsp. durum) in the Yaqui Valley, Mexico

Strain TSO2T, a plant growth-promoting rhizobacteria and biological control agent, was isolated from wheat rhizosphere sampled from the Yaqui Valley in Mexico. The strain was identified using a polyphasic approach. Based on its analysis of the full-length 16S rRNA gene, strain TSO2T was assigned to the genus Bacillus , which was supported by morphological and metabolic traits, such as Gram-positive staining, rod shape, spore formation, strictly aerobic metabolism, catalase-positive activity, starch, and casein hydrolysis, reduction of nitrate to nitrite, growth in presence of lysozyme and 2 % NaCl, citrate utilization, growth at pH 6.0, acid production from glucose and indole production from tryptophan. Additionally, strain TSO2T possesses swarming motility, presenting a featureless mat pattern that can cover the whole petri dish. The whole-genome phylogenetic relationship analysis elucidated that strain TSO2T is closely related to Bacillus cabrialesii TE3T. The maximum values for average nucleotide identity (ANI) and in silico DNA–DNA hybridization from the genome-to-genome distance calculator (GGDC) were 97 and 73.4 %, respectively, related to Bacillus cabrialesii TE3T, where both ANI and GGDC values were barely above the species delimitation threshold, but below the subspecies limit. Also, strain TSO2T showed the ability to produce a fatty acid (C18 : 0) that is not present in closely related Bacillus species. These results provide evidence that strain TSO2T is a novel subspecies of the species Bacillus cabrialesii , for which the name Bacillus cabrialesii subsp. tritici subsp. nov. is proposed. The type strain of Bacillus cabrialesii subsp. tritici subsp. nov. is TSO2T (CM-CNRG TB52T=LBPCV TSO2T). The description of this novel subspecies automatically creates the subspecies Bacillus cabrialesii subsp. cabrialesii subsp. nov. for which the type strain is TE3T (CM-CNRG TB54T=CCStamb A1T).

Antimicrobial activity and comparative metabolomic analysis of Priestia megaterium strains derived from potato and dendrobium

The growth of endophytic bacteria is influenced by the host plants and their secondary metabolites and activities. In this study, P. megaterium P-NA14 and P. megaterium D-HT207 were isolated from potato tuber and dendrobium stem respectively. They were both identified as Priestia megaterium. The antimicrobial activities and metabolites of both strains were explored. For antimicrobial activities, results showed that P. megaterium P-NA14 exhibited a stronger inhibition effect on the pathogen of dendrobium, while P. megaterium D-HT207 exhibited a stronger inhibition effect on the pathogen of potato. The supernatant of P. megaterium P-NA14 showed an inhibition effect only on Staphylococcus aureus, while the sediment of P. megaterium D-HT207 showed an inhibition effect only on Escherichia coli. For metabolomic analysis, the content of L-phenylalanine in P. megaterium P-NA14 was higher than that of P. megaterium D-HT207, and several key downstream metabolites of L-phenylalanine were associated with inhibition of S. aureus including tyrosine, capsaicin, etc. Therefore, we speculated that the different antimicrobial activities between P. megaterium P-NA14 and P. megaterium D-HT207 were possibly related to the content of L-phenylalanine and its metabolites. This study preliminarily explored why the same strains isolated from different hosts exhibit different activities from the perspective of metabolomics.

An agroecological structure model of compost-soil-plant interactions for sustainable organic farming

Compost is used worldwide as a soil conditioner for crops, but its functions have still been explored. Here, the omics profiles of carrots were investigated, as a root vegetable plant model, in a field amended with compost fermented with thermophilic Bacillaceae for growth and quality indices. Exposure to compost significantly increased the productivity, antioxidant activity, color, and taste of the carrot root and altered the soil bacterial composition with the levels of characteristic metabolites of the leaf, root, and soil. Based on the data, structural equation modeling (SEM) estimated that amino acids, antioxidant activity, flavonoids and/or carotenoids in plants were optimally linked by exposure to compost. The SEM of the soil estimated that the genus Paenibacillus and nitrogen compounds were optimally involved during exposure. These estimates did not show a contradiction between the whole genomic analysis of compost-derived Paenibacillus isolates and the bioactivity data, inferring the presence of a complex cascade of plant growth-promoting effects and modulation of the nitrogen cycle by the compost itself. These observations have provided information on the qualitative indicators of compost in complex soil-plant interactions and offer a new perspective for chemically independent sustainable agriculture through the efficient use of natural nitrogen.

Antifungal Activity and Effect of Plant-Associated Bacteria on Phenolic Synthesis of Quercus robur L

Europe's forests, particularly in Ukraine, are highly vulnerable to climate change. The maintenance and improvement of forest health are high-priority issues, and various stakeholders have shown an interest in understanding and utilizing ecological interactions between trees and their associated microorganisms. Endophyte microbes can influence the health of trees either by directly interacting with the damaging agents or modulating host responses to infection. In the framework of this work, ten morphotypes of endophytic bacteria from the tissues of unripe acorns of Quercus robur L. were isolated. Based on the results of the sequenced 16S rRNA genes, four species of endophytic bacteria were identified: Bacillus amyloliquefaciens, Bacillus subtilis, Delftia acidovorans, and Lelliottia amnigena. Determining the activity of pectolytic enzymes showed that the isolates B. subtilis and B. amyloliquefaciens could not cause maceration of plant tissues. Screening for these isolates revealed their fungistatic effect against phytopathogenic micromycetes, namely Fusarium tricinctum, Botrytis cinerea, and Sclerotinia sclerotiorum. Inoculation of B. subtilis, B. amyloliquefaciens, and their complex in oak leaves, in contrast to phytopathogenic bacteria, contributed to the complete restoration of the epidermis at the sites of damage. The phytopathogenic bacteria Pectobacterium and Pseudomonas caused a 2.0 and 2.2 times increase in polyphenol concentration in the plants, respectively, while the ratio of antioxidant activity to total phenolic content decreased. Inoculation of Bacillus amyloliquefaciens and Bacillus subtilis isolates into oak leaf tissue were accompanied by a decrease in the total pool of phenolic compounds. The ratio of antioxidant activity to total phenolic content increased. This indicates a qualitative improvement in the overall balance of the oak leaf antioxidant system induced by potential PGPB. Thus, endophytic bacteria of the genus Bacillus isolated from the internal tissues of unripe oak acorns have the ability of growth biocontrol and spread of phytopathogens, indicating their promise for use as biopesticides.

Synthesis and characterization of copper oxide nanoparticles: its influence on corn (Z. mays) and wheat (Triticum aestivum) plants by inoculation of Bacillus subtilis

Nanotechnology is now playing an emerging role in green synthesis in agriculture as nanoparticles (NPs) are used for various applications in plant growth and development. Copper is a plant micronutrient; the amount of copper oxide nanoparticles (CuONPs) in the soil determines whether it has positive or adverse effects. CuONPs can be used to grow corn and wheat plants by combining Bacillus subtilis. In this research, CuONPs were synthesized by precipitation method using different precursors such as sodium hydroxide (0.1 M) and copper nitrate (Cu(NO₃)₂) having 0.1 M concentration with a post-annealing method. The NPs were characterized through X-ray diffraction (XRD), scanning electron microscope (SEM), and ultraviolet (UV) visible spectroscopy. Bacillus subtilis is used as a potential growth promoter for microbial inoculation due to its prototrophic nature. The JAR experiment was conducted, and the growth parameter of corn (Z. mays) and wheat (Triticum aestivum) was recorded after 5 days. The lab assay evaluated the germination in JARs with and without microbial inoculation under CuONP stress at different concentrations (25 and 50 mg). The present study aimed to synthesize CuONPs and systematically investigate the particle size effects of copper (II) oxide (CuONPs) (< 50 nm) on Triticum aestivum and Z. mays. In our results, the XRD pattern of CuONPs at 500 °C calcination temperature with monoclinic phase is observed, with XRD peak intensity slightly increasing. The XRD patterns showed that the prepared CuONPs were extremely natural, crystal-like, and nano-shaped. We used Scherrer's formula to calculate the average size of the particle, indicated as 23 nm. The X-ray diffraction spectrum of synthesized materials and SEM analysis show that the particles of CuONPs were spherical in nature. The results revealed that the synthesized CuONPs combined with Bacillus subtilis used in a field study provided an excellent result, where growth parameters of Z. Mays and Triticum aestivum such as root length, shoot length, and plant biomass was improved as compared to the control group.

Bacillus subtilis and Bacillus licheniformis promote tomato growth

Bacillus spp. are widely marketed and used in agricultural systems as antagonists to various phytopathogens, but it can also benefit the plant as plant growth promoters. Therefore, the longer presence of the bacterium in the rhizosphere would result in a prolonged growth-promoting benefit, but little is yet known about its persistence in the rhizosphere after seed coating. The objectives of this study were to evaluate the tomato growth promotion mediated by Bacillus licheniformis FMCH001 and Bacillus subtilis FMCH002 and the survival rate of these bacteria both in shoots and in the rhizosphere. The Bacillus strains used throughout this study were obtained from Quartzo® produced by Chr. Hansen. The application of a mixture of B. subtilis and B. licheniformis (Quartzo®) at concentrations 1 × 108, 1 × 109, and 1 × 1010 CFU mL-1, as well as the application of B. subtilis and B. licheniformis individually at concentration 1 × 108 CFU mL-1, increased fresh and dry masses of shoot and root system, volume of root system, and length of roots of tomato plants when compared to control. Both Bacillus strains produced IAA after 48 h of in vitro. Bacillus colonies obtained from plant sap were morphologically similar to colonies of B. subtilis and B. licheniformis strains and were detected in inoculated on plants and not detected in control ones. A similar pattern was obtained through DNA-based detection (qPCR). Therefore, B. subtilis and B. licheniformis were able to produce auxin, promote tomato growth, and colonize and persist in the rhizosphere.

Azospirillum-Bacillus associations: synergistic effects on in vitro PGP traits and growth of pearl millet at early seedling stage under limited moisture conditions

The association of plant beneficial Azospirillum and Bacillus spp. strains expressing different sets of PGP traits may have complementary or supplementary effects on host plants. In the present investigation, A. formosense and Bacillus spp. strains showing diverse PGP traits (IAA production, nitrogenase activity, phosphate, zinc and potassium solubilization, siderophores, antagonism against phytopathogens, osmotic stress tolerance, etc.) were assessed for compatibility by cross-streaking and co-culturing. Under co-culture (Azospirillum + Bacillus), a significant increase in the expression of PGP traits, nitrogenase activity (up to 89%), phosphate solubilization (upto 236%), siderophore production (upto 20%) was observed as compared to individual Azospirillum culture, indicating synergistic effect of co-culture. IAA production was higher in Azospirillum sp. strains as compared to Bacillus spp. strains, when cultured individually; however, when co-cultured, the IAA levels were in the mid-range indicating the contributory effects of compatible strains. The effect of individual Azospirillum and Bacillus strains and their co-inoculation was also assessed on the growth of pearl millet at early stages under moisture-deficit stress imposed using PEG6000 (0, 10, and 20%). Co-inoculation enhanced seed germination (up to 10, 3, and 6% increase under 0, 10, and 20% PEG, respectively, over individual Azospirillum treatment), root traits (increased root hair density and lateral branches), and seedling vigor indices (up to 22, 32, 43% increase in seed vigor index I and 8, 14, and 10% increase in seed vigor index II under 0, 10, 20% PEG, respectively, over individual Azospirillum treatment) under normal as well as moisture-deficit conditions suggesting the role of Bacillus spp. strains in better adaptation of the plants to stress and higher yield potential. The synergistic effect of co-cultured Azospirillum and Bacillus strains on PGP traits indicated metabolic interplay between the two strains which needs to be further understood. The positive effect of co-inoculation on plant growth under moisture-deficit stress indicated the promise of Azospirillum and Bacillus as a synergistic bioformulation for combating nutrient and drought stress in pearl millet, particularly in nutrient-poor dryland agricultural systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03503-4.