Plant growth-promoting endophytic bacteria versus pathogenic infections: an example of Bacillus amyloliquefaciens RWL-1 and Fusarium oxysporum f. sp. lycopersici in tomato

Silicon: A valuable soil element for improving plant growth and CO2 sequestration

BACKGROUND

Silicon (Si), the second most abundant and quasi-essential soil element, is locked as a recalcitrant silicate mineral in the Earth's crust. The physical abundance of silicates can play an essential role in increasing plant productivity. Plants store Si as biogenic silica (phytoliths), which is mobilized through a chemical weathering process in the soil.

AIM OF REVIEW

Although Si is a critical element for plant growth, there is still a considerable need to understand its dissolution, uptake, and translocation in agroecosystems. Here, we show recent progress in understanding the interactome of Si, CO2, the microbiome, and soil chemistry, which can sustainably govern silicate dissolution and cycling in agriculture.

KEY SCIENTIFIC CONCEPTS OF THIS REVIEW

Si cycling is directly related to carbon cycling, and the resulting climate stability can be enhanced by negative feedback between atmospheric CO2 and the silicate uptake process. Improved Si mobilization in the rhizosphere by the presence of reactive elements (for example, Ca, Na, Al, Zn, and Fe) and Si uptake through genetic transporters in plants are crucial to achieving the dual objectives of (i) enhancing crop productivity and (ii) abiotic stress tolerance. Furthermore, the microbiome is a symbiotic partner of plants. Bacterial and fungal microbiomes can solubilize silicate minerals through intriguingly complex bioweathering mechanisms by producing beneficial metabolites and enzymes. However, the interaction of Si with CO2 and the microbiome's function in mobilization have been understudied. This review shows that enhancing our understanding of Si, CO2, the microbiome, and soil chemistry can help in sustainable crop production during climatic stress events.

Novel melatonin-producing Bacillus safensis EH143 mitigates salt and cadmium stress in soybean

Recently, microorganism and exogenous melatonin application has been recognized as an efficient biological tool for enhancing salt tolerance and heavy metal detoxification in agriculture crops. Thus, the goal of this study was to isolate and evaluate a novel melatonin-producing plant growth promoting bacterium. With high-throughput whole genome sequencing, phytohormone measurements, expression profiling, and biochemical analysis, we can identify a novel PGPB that produces melatonin and unravel how it promotes soybean growth and development and protects against salt and Cd stress. We identify the melatonin synthesis pathway (tryptophan→tryptamine→serotonin melatonin) of the halotolerant (NaCl > 800 mM) and heavy metal-resistant (Cd >3 mM) rhizobacterium Bacillus safensis EH143 and use it to treat soybean plants subjected to Cd and NaCl stresses. Results show that EH143 will highly bioaccumulate heavy metals and significantly improve P and Ca2+ uptake and the K+/Na+ (93%↑under salt stress) ratio while reducing Cd uptake (49% under Cd stress) in shoots. This activity was supported by the expression of the ion regulator HKT1, MYPB67, and the calcium sensors CDPK5 and CaMK1 which ultimately led to increased plant growth. EH143 significantly decreased ABA content in shoots by 13%, 20%, and 34% and increased SA biosynthesis in shoots by 14.8%, 31%, and 48.2% in control, salt, and Cd-treated plants, upregulating CYP707A1 and CYP707A2 and PAL1 and ICS, respectively. The melatonin content significantly decreased along with a reduced expression of ASMT3 following treatment with EH143; moreover, reduced expression of peroxidase (POD) and superoxide dismutase (SOD) by 134.5% and 39% under salt+Cd stress, respectively and increased level of total amino acids were observed. Whole-genome sequencing and annotation of EH143 revealed the presence of the melatonin precursor tryptophan synthase (trpA, trpB, trpS), metal and other ion regulators (Cd: cadA, potassium: KtrA and KtrB, phosphate: glpT, calcium: yloB, the sodium/glucose cotransporter: sgIT, and the magnesium transporter: mgtE), and enzyme activators (including the siderophore transport proteins yfiZ and yfhA, the SOD sodA, the catalase katA1, and the glutathione regulator KefG) that may be involved in programming the plant metabolic system. As a consequence, EH143 treatment significantly reduced the contents of lipid peroxidation (O2-, MDA, and H2O2) up to 69%, 46%, and 29% in plants under salt+Cd stress, respectively. These findings suggest that EH143 could be a potent biofertilizer to alleviate NaCl and Cd toxicity in crops and serve as an alternative substitute for exogenous melatonin application.

Bacterial endophytic community composition varies by hemp cultivar in commercially sourced seed

The seed-endophytic bacterial community is a potentially beneficial and heritable fraction of the plant microbiome. Its utilization as a sustainable crop improvement strategy could be especially valuable for species such as hemp, where production is being scaled up and new challenges will be faced in managing crop productivity and health. However, little is known about the makeup and variation of the hemp seed microbiome. This study profiled the endophytic bacterial communities harboured by 16 hemp cultivars sourced from commercial suppliers in Europe. A 16S rDNA amplicon sequencing approach identified 917 amplicon sequence variants across samples. Taxonomic classification of sequences revealed 4 phyla and 87 genera to be represented in the dataset. Several genera were widespread while some were specific to one or a few cultivars. Flavobacterium, Pseudomonas, and Pantoea were notable in their high overall abundance and prevalence, but community composition was variable and no one taxon was universally abundant, suggesting a high degree of flexibility in community assembly. Taxonomic composition and alpha diversity differed among cultivars, though further work is required to understand the relative influence of hemp genetic factors on community structure. The taxonomic profiles presented here can be used to inform further work investigating the functional characteristics and potential plant-growth-promoting traits of seed-borne bacteria in hemp.

Revealing the seed microbiome: Navigating sequencing tools, microbial assembly, and functions to amplify plant fitness

Microbial communities within seeds play a vital role in transmitting themselves to the next generation of plants. These microorganisms significantly impact seed vigor and early seedling growth, for successful crop establishment. Previous studies reported on seed-associated microbial communities and their influence on processes like dormancy release, germination, and disease protection. Modern sequencing and conventional methods reveal microbial community structures and environmental impacts, these information helps in microbial selection and manipulation. These studies form the foundation for using seed microbiomes to enhance crop resilience and productivity. While existing research has primarily focused on characterizing microbiota in dried mature seeds, a significant gap exists in understanding how these microbial communities assemble during seed development. The review also discusses applying seed-associated microorganisms to improve crops in the context of climate change. However, limited knowledge is available about the microbial assembly pattern on seeds, and their impact on plant growth. The review provides insight into microbial composition, functions, and significance for plant health, particularly regarding growth promotion and pest control.

Plant-Growth-Promoting Rhizobacteria Modulate Carbohydrate Metabolism in Connection with Host Plant Defense Mechanism

Plant-growth-promoting rhizobacteria (PGPR) could potentially enhance photosynthesis and benefit plant growth by improving soil nutrient uptake and affecting plant hormone balance. Several recent studies have unveiled a correlation between alterations in photosynthesis and host plant resistance levels. Photosynthesis provides materials and energy for plant growth and immune defense and affects defense-related signaling pathways. Photosynthetic organelles, which could be strengthened by PGPR inoculation, are key centers for defense signal biosynthesis and transmission. Although endophytic PGPRs metabolize plant photosynthates, they can increase soluble sugar levels and alternate sugar type and distribution. Soluble sugars clearly support plant growth and can act as secondary messengers under stressed conditions. Overall, carbohydrate metabolism modifications induced by PGPR may also play a key role in improving plant resistance. We provide a concise overview of current knowledge regarding PGPR-induced modulation in carbohydrate metabolism under both pathogen-infected and pathogen-free conditions. We highlight PGPR application as a cost-saving strategy amidst unpredictable pathogen pressures.

In vivo and In vitro evaluation of the antifungal activity of the PGPR Bacillus amyloliquefaciens RaSh1 (MZ945930) against Alternaria alternata with growth promotion influences on Capsicum annuum L. plants

Alternaria alternata that threatens pepper production and causes major economic harm is responsible for the leaf spot/blight disease. Chemical fungicides have been widely employed; unfortunately, fungicidal resistance is a current concern. Therefore, finding new environmentally friendly biocontrol agents is a future challenge. One of these friendly solutions is the use of bacterial endophytes that have been identified as a source of bioactive compounds. The current study investigates the in vivo and in vitro fungicidal potential of Bacillus amyloliquefaciens RaSh1 (MZ945930) against pathogenic A. alternata. In vitro, the results revealed that RaSh1 exhibited strong antagonistic activity against A. alternata. In addition to this, we inoculated pepper (Capsicum annuum L.) plants with B. amyloliquefaciens RaSh1 and infected them with A. alternata. As a result of A. alternata infection, which generated the highest leaf spot disease incidence (DI), the plant's growth indices and physio-biochemical characteristics significantly decreased, according to our findings. Our results also showed the abnormal and deformed cell structure using light and electron microscopy of A. alternata-infected leaves compared with other treatments. However, DI was greatly reduced with B. amyloliquefaciens RaSh1 application (40%) compared to pepper plants infected with A. alternata (80%), and this led to the largest increases in all identified physio-biochemical parameters, including the activity of the defense-related enzymes. Moreover, inoculation of pepper plants with B. amyloliquefaciens RaSh1 decreased electrolyte leakage by 19.53% and MDA content by 38.60% as compared to A. alternata infected ones. Our results show that the endophyte B. amyloliquefaciens RaSh1 has excellent potential as a biocontrol agent and positively affects pepper plant growth.

'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.

Metabolomic profiles of the liquid state fermentation in co-culture of Eurotium amstelodami and Bacillus licheniformis

As an important source of new drug molecules, secondary metabolites (SMs) produced by microorganisms possess important biological activities, such as antibacterial, anti-inflammatory, and hypoglycemic effects. However, the true potential of microbial synthesis of SMs has not been fully elucidated as the SM gene clusters remain silent under laboratory culture conditions. Herein, we evaluated the inhibitory effect of Staphylococcus aureus by co-culture of Eurotium amstelodami and three Bacillus species, including Bacillus licheniformis, Bacillus subtilis, and Bacillus amyloliquefaciens. In addition, a non-target approach based on ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) was used to detect differences in extracellular and intracellular metabolites. Notably, the co-culture of E. amstelodami and Bacillus spices significantly improved the inhibitory effect against S. aureus, with the combination of E. amstelodami and B. licheniformis showing best performance. Metabolomics data further revealed that the abundant SMs, such as Nummularine B, Lucidenic acid E2, Elatoside G, Aspergillic acid, 4-Hydroxycyclohexylcarboxylic acid, Copaene, and Pipecolic acid were significantly enhanced in co-culture. Intracellularly, the differential metabolites were involved in the metabolism of amino acids, nucleic acids, and glycerophospholipid. Overall, this work demonstrates that the co-culture strategy is beneficial for inducing biosynthesis of active metabolites in E. amstelodami and B. licheniformis.

Bacterial ACC deaminase: Insights into enzymology, biochemistry, genetics, and potential role in amelioration of environmental stress in crop plants

Growth and productivity of crop plants worldwide are often adversely affected by anthropogenic and natural stresses. Both biotic and abiotic stresses may impact future food security and sustainability; global climate change will only exacerbate the threat. Nearly all stresses induce ethylene production in plants, which is detrimental to their growth and survival when present at higher concentrations. Consequently, management of ethylene production in plants is becoming an attractive option for countering the stress hormone and its effect on crop yield and productivity. In plants, ACC (1-aminocyclopropane-1-carboxylate) serves as a precursor for ethylene production. Soil microorganisms and root-associated plant growth promoting rhizobacteria (PGPR) that possess ACC deaminase activity regulate growth and development of plants under harsh environmental conditions by limiting ethylene levels in plants; this enzyme is, therefore, often designated as a "stress modulator." TheACC deaminase enzyme, encoded by the AcdS gene, is tightly controlled and regulated depending upon environmental conditions. Gene regulatory components of AcdS are made up of the LRP protein-coding regulatory gene and other regulatory components that are activated via distinct mechanisms under aerobic and anaerobic conditions. ACC deaminase-positive PGPR strains can intensively promote growth and development of crops being cultivated under abiotic stresses including salt stress, water deficit, waterlogging, temperature extremes, and presence of heavy metals, pesticides and other organic contaminants. Strategies for combating environmental stresses in plants, and improving growth by introducing the acdS gene into crop plants via bacteria, have been investigated. In the recent past, some rapid methods and cutting-edge technologies based on molecular biotechnology and omics approaches involving proteomics, transcriptomics, metagenomics, and next generation sequencing (NGS) have been proposed to reveal the variety and potential of ACC deaminase-producing PGPR that thrive under external stresses. Multiple stress-tolerant ACC deaminase-producing PGPR strains have demonstrated great promise in providing plant resistance/tolerance to various stressors and, therefore, it could be advantageous over other soil/plant microbiome that can flourish under stressed environments.

Seed endophytic bacterial profiling from wheat varieties of contrasting heat sensitivity

Wheat yield can be limited by many biotic and abiotic factors. Heat stress at the grain filling stage is a factor that reduces wheat production tremendously. The potential role of endophytic microorganisms in mitigating plant stress through various biomolecules like enzymes and growth hormones and also by improving plant nutrition has led to a more in-depth exploration of the plant microbiome for such functions. Hence, we devised this study to investigate the abundance and diversity of wheat seed endophytic bacteria (WSEB) from heat^S (heat susceptible, GW322) and heat^T (heat tolerant, HD3298 and HD3271) varieties by culturable and unculturable approaches. The results evidenced that the culturable diversity was higher in the heat^S variety than in the heat^T variety and Bacillus was found to be dominant among the 10 different bacterial genera identified. Though the WSEB population was higher in the heat^S variety, a greater number of isolates from the heat^T variety showed tolerance to higher temperatures (up to 55°C) along with PGP activities such as indole acetic acid (IAA) production and nutrient acquisition. Additionally, the metagenomic analysis of seed microbiota unveiled higher bacterial diversity, with a predominance of the phyla Proteobacteria covering >50% of OTUs, followed by Firmicutes and Actinobacteria. There were considerable variations in the abundance and diversity between heat sensitivity contrasting varieties, where notably more thermophilic bacterial OTUs were observed in the heat^T samples, which could be attributed to conferring tolerance against heat stress. Furthermore, exploring the functional characteristics of culturable and unculturable microbiomes would provide more comprehensive information on improving plant growth and productivity for sustainable agriculture.

Use of beneficial bacterial endophytes: A practical strategy to achieve sustainable agriculture

Beneficial endophytic bacteria influence their host plant to grow and resist pathogens. Despite the advantages of endophytic bacteria to their host, their application in agriculture has been low. Furthermore, many plant growers improperly use synthetic chemicals due to having no or little knowledge of the role of endophytic bacteria in plant growth, the prevention and control of pathogens and poor access to endobacterial bioproducts. These synthetic chemicals have caused soil infertility, environmental contamination, disruption to ecological cycles and the emergence of resistant pests and pathogens. There is more that needs to be done to explore alternative ways of achieving sustainable plant production while maintaining environmental health. In recent years, the use of beneficial endophytic bacteria has been noted to be a promising tool in promoting plant growth and the biocontrol of pathogens. Therefore, this review discusses the roles of endophytic bacteria in plant growth and the biocontrol of plant pathogens. Several mechanisms that endophytic bacteria use to alleviate plant biotic and abiotic stresses by helping their host plants acquire nutrients, enhance plant growth and development and suppress pathogens are explained. The review also indicates that there is a gap between research and general field applications of endophytic bacteria and suggests a need for collaborative efforts between growers at all levels. Furthermore, the presence of scientific and regulatory frameworks that promote advanced biotechnological tools and bioinoculants represents major opportunities in the applications of endophytic bacteria. The review provides a basis for future research in areas related to understanding the interactions between plants and beneficial endophytic microorganisms, especially bacteria.

Biological Control of Verticillium Wilt and Growth Promotion in Tomato by Rhizospheric Soil-Derived Bacillus amyloliquefaciens Oj-2.16

Verticillium wilt disease caused by Verticillium dahliae seriously affects tomato quality and yield. In this work, strain Oj-2.16 was isolated from rhizosphere soil of the medicinal plant Ophiopogon japonicas and identified as Bacillus amyloliquefaciens on the basis of morphological, physiological, and biochemical characteristics and 16S rDNA sequencing. Strain Oj-2.16 exhibited a high inhibition rate against V. dahliae, and the hyphae inhibited by Oj-2.16 were found to be destroyed on scanning electron microscopy. Lipopeptide and dipeptide genes were detected in the Oj-2.16 genome by PCR amplification involved in surfactin, iturin, fengycin, and bacilysin biosynthesis. In pot experiments, the biocontrol efficacy of strain Oj-2.16 against Verticillium wilt in tomato was 89.26%, which was slightly higher than the efficacy of the chemical fungicide carbendazim. Strain Oj-2.16 can produce indole acetic acid, siderophores, assimilate various carbon sources, and significantly promoted the growth of tomato seedlings by increasing plant height, root length, stem width, fresh weight, and dry weight by 44.44%, 122.22%, 80.19%, 57.65%, 64.00%, respectively. Furthermore, defense-related antioxidant CAT, SOD, POD, and PAL enzyme activities significantly increased and MDA contents significantly decreased in tomato seedlings treated with strain Oj-2.16 upon inoculation of V. dahliae compared with the pathogen-inoculated control. In summary, we concluded that B. amyloliquefaciens Oj-2.16 could be used as a promising candidate for the biocontrol of Verticillium wilt and as plant growth stimulator of tomato.

Characterization of Seed Mycobiota Using Culture-Dependent and Culture-Independent Approaches

Seed fungi are potentially important for their roles in seedling microbiome assembly and seedling health, but surveys of full seed fungal communities remain limited. While culture-dependent methods have been used to characterize some members of the seed mycobiota, recent culture-independent studies have improved the ease in identifying and characterizing full seed fungal communities. In this chapter, we describe how to survey seed fungi using both traditional culture-based methods and culture-free metabarcoding. We first describe protocols for the isolation and long-term preservation of fungal strains from individual seeds and for the extraction and amplification of DNA from such fungal isolates for identification with Sanger sequencing. We also detail how to extract, amplify, and sequence fungal DNA directly from individual seeds. Finally, we provide suggestions for troubleshooting media choices, PCR inhibition by isolates and plant tissue, and PCR limitation by low fungal DNA.

Dynamic changes in the endophytic bacterial community during maturation of Amorphophallus muelleri seeds

The seed microbiota is considered to be the starting point of the accumulation of plant microbiota, which is conducive to the preservation and germination of seeds and the establishment and development of seedlings. Our understanding of the colonization and migration dynamics of microbial taxa during seed development and maturation is still limited. This study used 16S rRNA high-throughput sequencing to investigate the dynamic changes in the composition and diversity of the endophytic bacterial community during maturation of Amorphophallus muelleri seeds. The results showed that as seeds matured (green to red), the Shannon index of their endophytic bacterial community first decreased and then increased, and the ACE and Chao1 indices of the endophytic bacterial community decreased gradually. The Shannon, ACE, and Chao1 indices of the endophytic bacterial community in the seed coat first decreased and then increased. Principal coordinate analysis of the bacterial communities revealed that the seed coat at different maturity stages showed significantly distinct bacterial communities and formed different clusters according to maturity stage. The bacterial communities of green and red seeds showed a clear separation, but they both overlapped with those of yellow seeds, indicating that some core taxa were present throughout seed maturation, but their relative abundance was dynamically changing. As the seeds grew more mature, the relative abundance of some bacterial communities with plant growth-promoting traits and others correlated with plant resistance (e.g., Burkholderia-Caballeronia-Paraburkholderia, Bacillus, Pseudomonas, Bradyrhizobium, Streptomyces) tended to increase and peaked in fully mature seeds and seed coats. The endophytic bacterial community of A. muelleri seeds seems to be driven by the seed maturation state, which can provide a theoretical basis for a comprehensive understanding of the assembly process of the microbial community during A. muelleri seed maturation.

Evaluation of the Antifungal Activity of Bacillusamyloliquefaciens and B. velezensis and Characterization of the Bioactive Secondary Metabolites Produced against Plant Pathogenic Fungi

Endophytic bacteria are plant-beneficial bacteria with a broad host range. They provide numerous benefits to their hosts, helping them tolerate several biotic and abiotic stresses. An interest has recently been developed in endophytic bacteria which are producing bioactive compounds that contribute to the biological control of various phytopathogens. This research paper aimed to investigate the potentiality of new local strains of endophytic bacteria such as Bacillus amyloliquefaciens and B. velezensis and the production of several antimicrobial metabolites associated with the biocontrol of Alternaria sp., which cause serious diseases and affect important vegetable crops in Egypt. Twenty-five endophytic bacteria isolates were obtained from different plants cultivated in El-Sharkia Governorate, Egypt. Dual culture technique was used to evaluate the bacterial isolates' antagonistic potentiality against Alternaria sp. and Helminthosporium sp. The most active bacterial isolates obtained were selected for further screening. The antifungal activity of the most active endophytic bacterial isolate was assessed in vivo on pepper seedlings as a biocontrol agent against Alternaria sp. A significant antifungal activity was recorded with isolates C₁ and T₅ against Alternaria sp. and Helminthosporium sp. The bacterial endophyte discs of C₁ and T₅ showed the highest inhibitory effect against Alternaria sp. at 4.7 and 3.1 cm, respectively, and Helminthosporium sp. at 3.9 and 4.0 cm, respectively. The most active endophytic isolates C₁ and T₅ were identified and the 16S rRNA sequence was submitted to the NCBI GenBank database with accession numbers: MZ945930 and MZ945929 for Bacillus amyloliquefaciens and Bacillus velezensis, respectively. The deformity of pathogenic fungal mycelia of Alternaria sp. and Helminthosporium sp. was studied under the biotic stress of bacteria. The culture filtrates of B. amyloliquefaciens and B. velezensis were extracted with different solvents, and the results indicated that hexane was the most efficient. Gas Chromatography-Mass Spectrometry revealed that Bis (2-ethylhexyl) phthalate, Bis (2-ethylhexyl) ester, and N,N-Dimethyldodecylamine were major constituents of the endophytic crude extracts obtained from B. amyloliquefaciens and B. velezensis. The in vivo results showed that Alternaria sp. infection caused the highest disease incidence, leading to a high reduction in plant height and in the fresh and dry weights of pepper plants. With B. amyloliquefaciens application, DI significantly diminished compared to Alternaria sp. infected pepper plants, resulting in an increase in their morphological parameters. Our findings allow for a reduction of chemical pesticide use and the control of some important plant diseases.

Bacterial bioinoculants adapted for sustainable plant health and soil fertility enhancement in Namibia

The increase in dryland agriculture elicits the need to develop sustainable practices that improve crop yield and protect soil fertility. The use of biofertilisers adapted to nutrient deficient soils and arid climates would help achieve this. In this review, the use of plant growth-promoting bacteria is explored as a possible solution to the current state of dryland agriculture and climate change threats to agriculture. Plant microbe interactions form the basis of this review as evidence has shown that these interactions often exist to improve the health of plants. This is achieved by the production of important biochemicals and enzymes like indole acetic acid and amino cyclopropane-1-carboxylate deaminase while also actively protecting plants from pathogens including fungal pathogens. Research, therefore, has shown that these plant-growth promoting bacteria may be exploited and developed into biofertilisers. These biofertilisers are both economically and environmentally sustainable while improving soil quality and crop yield. The literature presented in this review is in context of the Namibian climate and soil profiles.

The Combined Inoculation of Curvularia lunata AR11 and Biochar Stimulates Synthetic Silicon and Potassium Phosphate Use Efficiency, and Mitigates Salt and Drought Stresses in Rice

Synthetic chemical fertilizers are a fundamental source of nutrition for agricultural crops; however, their limited availability, low plant uptake, and excessive application have caused severe ecological imbalances. In addition, the gravity of environmental stresses, such as salinity and water stress, has already exceeded the threshold limit. Therefore, the optimization of nutrient efficiency in terms of plant uptake is crucial for sustainable agricultural production. To address these challenges, we isolated the rhizospheric fungus Curvularia lunata ARJ2020 (AR11) and screened the optimum doses of biochar, silicon, and potassium phosphate (K2HPO4), and used them-individually or jointly-to treat rice plants subjected to salt (150 mM) and drought stress (20-40% soil moisture). Bioassay analysis revealed that AR11 is a highly halotolerant and drought-resistant strain with an innate ability to produce gibberellin (GA1, GA3, GA4, and GA7) and organic acids (i.e., acetic, succinic, tartaric, and malic acids). In the plant experiment, the co-application of AR11 + Biochar + Si + K2HPO4 significantly improved rice growth under both salt and drought stresses. The plant growth regulator known as abscisic acid, was significantly reduced in co-application-treated rice plants exposed to both drought and salt stress conditions. These plants showed higher Si (80%), P (69%), and K (85%) contents and a markedly low Na+ ion (208%) concentration. The results were further validated by the higher expression of the Si-carrying gene OsLSi1, the salt-tolerant gene OsHKT2, and the OsGRAS23's drought-tolerant transcriptome. Interestingly, the beneficial effect of AR11 was significantly higher than that of the co-application of Biochar + Si + K2HPO4 under drought. Moreover, the proline content of AR11-treated plants decreased significantly, and an enhancement of plant growth-promoting characteristics was observed. These results suggest that the integrated co-application of biochar, chemical fertilizers, and microbiome could mitigate abiotic stresses, stimulate the bioavailability of essential nutrients, relieve phytotoxicity, and ultimately enhance plant growth.

Metalliferous habitats and seed microbes affect the seed morphology and reproductive strategy of Arabidopsis halleri

Purpose

Plant reproduction in metalliferous habitats is challenged by elevated concentrations of metal trace elements in soil. As part of their survival strategy, metal-tolerant plants have adjusted reproductive traits, including seed morphology, dormancy, and germination rate. These traits are particularly relevant, yet poorly understood, in metal hyperaccumulators that are promising candidates for phytoremediation.

Methods

We assessed seed shape characteristics, dormancy, and germination rate in the hyperaccumulating model species Arabidopsis halleri. Seed morphological parameters were evaluated using seeds collected from two metalliferous and two non-metalliferous sites (~ 1000 seeds per location). We also addressed the potential influence of seed surface-associated microbes and endophytic fungi on germination success.

Results

Seeds from non-metallicolous populations were on average 18% bigger than those from metal-contaminated post-mining sites, which contrasts the general expectation about reproductive parts in metallicolous plants. Irrespective of their origin, surface-sterilized seeds had up to ~ 20% higher germination rates and germinated earlier than non-sterilized seeds, hinting at a negative effect of seed-associated microbial communities. Surface sterilization also facilitated the emergence of an endophytic fungus (Aspergillus niger) that is a known seed-borne pathogen. Interestingly, A. niger actually promoted germination in surface-sterilized seeds from some locations.

Conclusion

Despite species-wide metal tolerance in A. halleri, metalliferous conditions seem to differently affect reproductive traits compared to non-metalliferous environments (e.g., smaller seeds). Yet, higher germination rates in these populations hint at the potential of A. halleri to successfully colonize post-mining habitats. This process is modulated by site-specific interactions with seed microbiota.

Biological Potentials and Phytochemical Constituents of Raw and Roasted Nigella arvensis and Nigella sativa

Nigella species are widely used to cure various ailments. Their health benefits, particularly from the seed oils, could be attributed to the presence of a variety of bioactive components. Roasting is a critical process that has historically been used to facilitate oil extraction and enhance flavor; it may also alter the chemical composition and biological properties of the Nigella seed. The aim of this study was to investigate the effect of the roasting process on the composition of the bioactive components and the biological activities of Nigella arvensis and Nigella sativa seed extracts. Our preliminary study showed that seeds roasted at 50 °C exhibited potent antimicrobial activities; therefore, this temperature was selected for roasting Nigella seeds. For extraction, raw and roasted seed samples were macerated in methanol. The antimicrobial activities against Streptococcus agalactiae, Streptococcus epidermidis, Streptococcus pyogenes, Candida albicans, Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, and Klebsiella oxytoca were determined by measuring the diameter of the zone of inhibition. The cell viability of extracts was tested in a colon carcinoma cell line, HCT-116, by using a microculture tetrazolium technique (MTT) assay. Amino acids were extracted and quantified using an automatic amino acid analyzer. Then, gas chromatography–mass spectrometry (GC–MS) analysis was performed to identify the chemical constituents and fatty acids. As a result, the extracts of raw and roasted seeds in both Nigella species showed strong inhibition against Klebsiella oxytoca, and the raw seed extract of N.arvensis demonstrated moderate inhibition against S. pyogenes. The findings of the MTT assay indicated that all the extracts significantly decreased cancer cell viability. Moreover, N. sativa species possessed higher contents of the measured amino acids, except tyrosine, cystine, and methionine. The GC–MS analysis of extracts showed the presence of 22 and 13 compounds in raw and roasted N. arvensis, respectively, and 9 and 11 compounds in raw and roasted N. sativa, respectively. However, heat treatment decreased the detectable components to 13 compounds in roasted N. arvensis and increased them in roasted N. sativa. These findings indicate that N. arvensis and N. sativa could be potential sources of anticancer and antimicrobials, where the bioactive compounds play a pivotal role as functional components.

Diversity and Plant Growth-Promoting Ability of Endophytic, Halotolerant Bacteria Associated with Tetragonia tetragonioides (Pall.) Kuntze

The diversity of salt-tolerant cultivable endophytic bacteria associated with the halophyte New Zealand spinach (Tetragonia tetragonioides (Pall.) Kuntze) was studied, and their plant beneficial properties were evaluated. The bacteria isolated from leaves and roots belonged to Agrobacterium, Stenotrophomonas, Bacillus, Brevibacterium, Pseudomonas, Streptomyces, Pseudarthrobacter, Raoultella, Curtobacterium, and Pantoea. Isolates exhibited plant growth-promoting traits, including the production of a phytohormone (indole 3-acetic-acid), cell wall degrading enzymes, and hydrogen cyanide production. Furthermore, antifungal activity against the plant pathogenic fungi Fusarium solani, F. oxysporum, and Verticillium dahliae was detected. Ten out of twenty bacterial isolates were able to synthesize ACC deaminase, which plays a vital role in decreasing ethylene levels in plants. Regardless of the origin of isolated bacteria, root or leaf tissue, they stimulated plant root and shoot growth under 200 mM NaCl conditions. Our study suggests that halophytes such as New Zealand spinach are a promising source for isolating halotolerant plant-beneficial bacteria, which can be considered as potentially efficient biofertilizers in the bioremediation of salt-affected soils.

Molecular and Biochemical Characterization, Antimicrobial Activity, Stress Tolerance, and Plant Growth-Promoting Effect of Endophytic Bacteria Isolated from Wheat Varieties

Endophytic bacteria have been utilized as an alternative source to chemical fertilizers and pesticides to enhance plant productivity and defense mechanisms against biotic and abiotic stress. Five endophytic bacterial strains were isolated from the seeds of three different Pakistani wheat varieties (Ghaneemat-e-IBGE, Atta-Habib, and Siren). The isolated strains AH-1, S-5, S-7, GI-1, and GI-6 showed phylogenetic similarity with Bacillus altitudinis, B. aryabhattai, B. wiedmannii, Pseudomonas aeruginosa, and Burkholderia gladioli, respectively. All strains showed catalase activity (except AH-1) and Indole-3-acetic acid production, with the highest concentration (16.77 μg·mL^-1) found for GI-6, followed by S-5 (11.5 μg·mL^-1), nitrogen assimilation (except S-7), phosphorus solubilization (except S-7 and AH-1), and ability to produce siderophores, with maximum productions for GI-6 (31 ± 3.5 psu) and GI-1 (30 ± 2.9 psu). All five analyzed strains possessed antimicrobial activity, which was particularly strong in GI-6 and S-5 against Klebsiella pneumonia, Escherichia coli, and Bacillus subtilis. Increasing salinity stress with NaCl negatively affected the bacterial growth of all isolates. However, strains GI-6 and S-5 showed salt tolerance after three days of incubation. A drought tolerance test resulted in a negative impact of poly ethylene glycol on bacterial growth, which was, however, less pronounced in GI-6 strain. The GI-6 strain revealed growth-promoting effects on inoculated wheat plants.

Bacillus subtilis HSY21 can reduce soybean root rot and inhibit the expression of genes related to the pathogenicity of Fusarium oxysporum

Soybean root rot occurs globally and seriously affects soybean production. To avoid the many disadvantages of chemical fungicides, the addition of Bacillus is gradually becoming an alternative strategy to tackle soybean root rot. However, the molecular mechanism of phytopathogenic fungi in this process by Bacillus inhibition is rarely reported. In this study, we isolated a strain of B. subtilis HSY21 from soybean rhizosphere soil, which had an inhibition rate of 81.30 ± 0.15% (P < 0.05) against Fusarium oxysporum. The control effects of this strain against soybean root rot under greenhouse and field conditions were 63.83% and 57.07% (P < 0.05), respectively. RNA-seq analysis of F. oxysporum after treatment with strain HSY21 revealed 1445 downregulated genes and 1561 upregulated genes. Among them, genes involved in mycelial growth, metabolism regulation, and disease-related enzymes were mostly downregulated. The activities of cellulase, β-glucosidase, α-amylase, and pectin-methyl- galacturonase as well as levels of oxalic acid and ergosterol in F. oxysporum were significantly decreased after HSY21 treatment. These results demonstrated that B. subtilis HSY21 could effectively control F. oxysporum by inhibiting its growth and the expression of pathogenic genes, thus indicating that this strain may be an ideal candidate for the prevention and control of soybean root rot.

Influence of the Rhizobacterium Rhodobacter sphaeroides KE149 and Biochar on Waterlogging Stress Tolerance in Glycine max L

In the context of the current climate change and increasing population scenarios, waterlogging stress in plants represents a global threat to sustainable agriculture production. Plant-growth-promoting rhizobacteria and biochar have been widely reported to mitigate the effects of several abiotic stresses. Hence, in the present study, we examined the effect of the rhizobacterium Rhodobacter sphaeroides KE149 and biochar on soybean plants subjected to sufficient water supply and waterlogging stress conditions. Our results revealed that KE149 and biochar inoculation significantly improved plant morphological attributes, such as root length, shoot length, and fresh biomass. The biochemical analysis results showed that the two treatments determined a significant drop in the levels of endogenous phytohormones (such as abscisic acid) under normal conditions, which were considerably enhanced under waterlogging stress. However, the jasmonic acid content increased with the application of biochar and KE149 under normal conditions, and it considerably decreased under waterlogging stress. Moreover, proline, methionine, and aspartic acid were significantly increased, whereas the phenolic and flavonoid contents were reduced with the application of the two treatments under waterlogging stress. These results suggest that the application of KE149 and biochar can be a safe biological tool with which to improve the physiology and productivity of soybean plants exposed to waterlogging stress.

Stimulation of Nicotiana tabacum L. In Vitro Shoot Growth by Endophytic Bacillus cereus Group Bacteria

In vitro plant tissue cultures face various unfavorable conditions, such as mechanical damage, osmotic shock, and phytohormone imbalance, which can be detrimental to culture viability, growth efficiency, and genetic stability. Recent studies have revealed a presence of diverse endophytic bacteria, suggesting that engineering of the endophytic microbiome of in vitro plant tissues has the potential to improve their acclimatization and growth. Therefore, the aim of this study was to identify cultivated tobacco (Nicotiana tabacum L.) endophytic bacteria isolates that are capable of promoting the biomass accumulation of in vitro tobacco shoots. Forty-five endophytic bacteria isolates were obtained from greenhouse-grown tobacco plant leaves and were assigned to seven Bacillus spp. and one Pseudomonas sp. based on 16S rRNA or genome sequence data. To evaluate the bacterial effect on in vitro plant growth, tobacco shoots were inoculated with 22 isolates selected from distinct taxonomic groups. Four isolates of Bacillus cereus group species B. toyonensis, B. wiedmannii and B. mycoides promoted shoot growth by 11-21%. Furthermore, a contrasting effect on shoot growth was found among several isolates of the same species, suggesting the presence of strain-specific interaction with the plant host. Comparative analysis of genome assemblies was performed on the two closely related B. toyonensis isolates with contrasting plant growth-modulating properties. This revealed distinct structures of the genomic regions, including a putative enzyme cluster involved in the biosynthesis of linear azol(in)e-containing peptides and polysaccharides. However, the function of these clusters and their significance in plant-promoting activity remains elusive, and the observed contrasting effects on shoot growth are more likely to result from genomic sequence variations leading to differences in metabolic or gene expression activity. The Bacillus spp. isolates with shoot-growth-promoting properties have a potential application in improving the growth of plant tissue cultures in vitro.

Bacillus pumilus induced tolerance of Maize (Zea mays L.) against Cadmium (Cd) stress

Heavy metals contaminate the soil that alters the properties of soil and negatively affect plants growth. Using microorganism and plant can remove these pollutants from soil. The present investigation was designed to evaluate the induced effect of Bacillus pumilus on maize plant in Cadmium (Cd) contaminated soil. Three different concentrations of Cd (i.e. 0.25, 0.50 and 0.75 mg kg^-1) were applied in soil under which maize plants were grown. The germination percentage, shoot length, leaf length, number of leaves, root length, fresh weight and nutrient uptake by maize plant were determined. The experiment was conducted by using complete randomized design (CRD) with three replicates. The result indicated that germination percentage, Shoot length, leaf length, root length, number of leaves, and plant fresh weight were reduced by 37, 39, 39, 32 and 59% respectively at 0.75 mg kg^-1 of CdSO₄ concentration but when maize seeds inoculated with Bacillus pumilus significantly increased the germination percentage, shoot length, leaf length, number of leaves, plant fresh weight at different concentrations of CdSO₄. Moreover, the plant protein were significantly increased by 60% in T6 (0.25 mg kg^-1 of CdSO₄ + inoculated seed) and Peroxidase dismutase (POD) was also significantly higher by 346% in T6 (0.25 mg kg^-1 of CdSO₄ + inoculated seed), however, the Superoxide dismutase (SOD) was significantly higher in T5 (0.75 mg kg^-1 of CdSO₄ + uninoculated seed) and was 769% higher as compared to control. The Cd contents in Bacillus pumilus inoculated maize roots and shoots were decreased. The present investigations indicated that the inoculation of maize plant with Bacillus pumilus can help maize plants to withstand Cd stress but higher concentration of Cd can harm the plant. The Bacillus pumilus has good potential to remediate Cd from soil, and also have potential to reduce the phyto availability and toxicity of Cd.

Green Fluorescent Protein-Tagged Bacillus axarquiensis TUBP1 Reduced Cotton Verticillium Wilt Incidence by Altering Soil Rhizosphere Microbial Communities

Verticillium wilt is a major disease of cotton that considerably decreases yield and crop quality. Soil microbial communities play an important role in plant health. Therefore, biocontrol bacteria that regulate microbial communities in rhizosphere soil can improve plant resistance to pathogens. Previously, the antagonistic strain Bacillus axarquiensis TUBP1 was screened and found to act against Verticillium dahliae with 43% biocontrol effect in cotton fields. We studied the effect of Bacillus axarquiensis TUBP1 with a green fluorescent protein (GFP) gene marker on the microbial community structure of cotton rhizosphere soil and cotton yield and quality. Cotton Verticillium wilt incidence, soil biochemical properties, and soil bacterial and fungal communities were analyzed. Results showed that bacterial and fungal abundance in cotton rhizosphere soil was temporarily changed after applying B. axarquiensis TUBP-315GFP. However, Bacillus significantly increased, whereas V. dahliae significantly decreased. The incidence of cotton Verticillium wilt after treatment with B. axarquiensis TUBP-315GFP was significantly lower and cotton production increased by 40.6%. Our findings indicated that the application of B. axarquiensis TUBP-315GFP can change microbial community structure of cotton rhizosphere soil, leading to a reduction in the incidence of cotton Verticillium wilt and increasing cotton yield.

Endophytic Bacillus Bacteria Living in Sugarcane Plant Tissues and Telchin licus licus Larvae (Drury) (Lepidoptera: Castniidae): The Symbiosis That May Open New Paths in the Biological Control

Bacteria of the genus Bacillus can colonize endophytically and benefit several crops including the control of some pest orders. In view of the benefits provided by these microorganisms and in order to find out an efficient biotechnological control for the giant borer, our interest in studying the microorganisms in symbiosis with sugarcane and the giant borer has arisen, since there is no efficient chemical or biological control method for this pest. Therefore, endophytic Bacillus strains were isolated from three sugarcane niches (apoplast fluid, central internode cylinder and roots) and also from the giant borer larvae living inside sugarcane varieties grown in the Northeast region of Brazil. The taxonomical characterization (16S rRNA) of 157 Gram-positive isolates showed that 138 strains belonged to the Bacillus genus. The most representative species were phylogenetically closely related to B. megaterium (11.5%) followed by B. safensis (10.8%), B. cereus (8.9%), B. oleronius (8.9%), B. amyloliquefaciens (7.0%), and B. pacificus (6.4%). BOX-PCR analyses showed very distinct band pattern profiles suggesting a great diversity of Bacillus species within the sugarcane niches and the digestive tract, while the B. cereus group remained very closely clustered in the dendrogram. According to XRE biomarker analysis, eleven strains (FORCN005, 007, 008, 011, 012, 014, 067, 076, 092, 093, and 135) correspond to B. thuringiensis species. Additional studies using conserved genes (glp, gmk, pta, and tpi) indicated that most of these strains were phylogenetically closely related to B. thuringiensis and may be considered different subspecies. In conclusion, this study suggests that the culturable Bacillus species are greatly diversified within the plant niches and showed Bacillus species in the digestive tract of the giant borer for the first time. These results open new perspectives to understand the role and functions played by these microorganisms in symbiosis with this pest and also the possibility of developing an efficient biological control method for the giant borer using strains identified as the B. thuringiensis species.

Evaluation potential of PGPR to protect tomato against Fusarium wilt and promote plant growth

Soilborne fungal diseases are most common among vegetable crops and have major implications for crop yield and productivity. Eco-friendly sustainable agriculture practices that can overcome biotic and abiotic stresses are of prime importance. In this study, we evaluated the ability of plant growth-promoting rhizobacterium (PGPR) Bacillus aryabhattai strain SRB02 to control the effects of tomato wilt disease caused by Fusarium oxysporum f. sp. lycopersici (strain KACC40032) and promote plant growth. In vitro bioassays showed significant inhibition of fungal growth by SRB02. Inoculation of susceptible and tolerant tomato cultivars in the presence of SRB02 showed significant protection of the cultivar that was susceptible to infection and promotion of plant growth and biomass production in both of the cultivars. Further analysis of SRB02-treated plants revealed a significantly higher production of amino acids following infection by F. oxysporum. Analysis of plant defense hormones after inoculation by the pathogen revealed a significantly higher accumulation of salicylic acid (SA), with a concomitant reduction in jasmonic acid (JA). These results indicate that B. aryabhattai strain SRB02 reduces the effects of Fusarium wilt disease in tomato by modulating endogenous phytohormones and amino acid levels.

Multifaceted intervention of Bacillus spp. against salinity stress and Fusarium wilt in tomato

AIM

This study aimed to screen halotolerant Bacillus strains able to promote growth and protect tomato plants against salt stress and Fusarium wilt (Fusarium oxysporum f. sp. lycopersici).

METHODS AND RESULTS

We evaluated some halotolerant strains of Bacillus spp. (Bacillus velezensis (AP-3) and Bacillus spp. (AP-6, AP-85 and AP-100)) to promote growth of tomato plants grown under salinity stress conditions and to protect them against Fusarium wilt disease. Such strains had been previously selected among 154 bacterial strains through biochemical tests (siderophores and indoleacetic acid productions, cellulase and catalase activity, nitrogen fixation and phosphate solubilization) in the presence of 100-mmol l^-1 NaCl. Besides the above-mentioned strains, B. subtilis QST-713 (Serenade^TM ) was also evaluated. Compared to control plants, aboveground dry weight increased in plants inoculated with AP-6, AP-85, AP-3, AP-100 and QST-713 strains developed in the absence of salt stress. The same tendency occurred for root dry weight; however, AP-3 strain was more effective, promoting an increase of 163%, when compared to control. Chlorophyll index and height increased >40 and 53%, respectively, for all Bacillus strains. Saline stress reduced plant growth regardless of the presence of Bacillus. Height, stem diameter, and aboveground and root dry weights increased in plants treated with Bacillus strains grown under saline conditions when compared to control. Bacillus velezensis AP-3 reduced the severity of Fusarium wilt in tomato by 50% when compared to control.

CONCLUSION

Halotolerant Bacillus strains controlled tomato Fusarium wilt, increased growth as well as tolerance to salt stress.

SIGNIFICANCE AND IMPACT OF THE STUDY

We demonstrated the efficacy of halotolerant Bacillus strains to control Fusarium wilt and improve tomato growth. We also demonstrated that these Bacillus strains protect tomato plants against salt stress. Bacillus can be used in an eco-friendly way because they are considered Generally Recognized As Safe.

Biodiversity and antimicrobial potential of bacterial endophytes from halophyte Salicornia brachiata

Extreme natural habitats like halophytes, marsh land, and marine environment are suitable arena for chemical ecology between plants and microbes having environmental impact. Endophytes are an ecofriendly option for the promotion of plant growth and to serve as sustainable resource of novel bioactive natural products. The present study, focusing on biodiversity of bacterial endophytes from Salicornia brachiata, led to isolation of around 336 bacterial endophytes. Phylogenetic analysis of 63 endophytes revealed 13 genera with 27 different species, belonging to 3 major groups: Firmicutes, Proteobacteria, and Actinobacteria. 30% endophytic isolates belonging to various genera demonstrated broad-spectrum antibacterial and antifungal activities against a panel of human, plant, and aquatic infectious agents. An endophytic isolate Bacillus amyloliquefaciens 5NPA-1, exhibited strong in-vitro antibacterial activity against human pathogen Staphylococcus aureus and phytopathogen Xanthomonas campestris. Investigation through LC-MS/MS-based molecular networking and bioactivity-guided purification led to the identification of three bioactive compounds belonging to lipopeptide class based on ¹H-, ¹³C-NMR and MS analysis. To our knowledge, this is the first report studying bacterial endophytic biodiversity of Salicornia brachiata and the isolation of bioactive compounds from its endophyte. Overall, the present study provides insights into the diversity of endophytes associated with the plants from the extreme environment as a rich source of metabolites with remarkable agricultural applications and therapeutic properties.

A prospectus of plant growth promoting endophytic bacterium from orchid (Vanda cristata)

Background

A plant growth-promoting endophytic bacterium PVL1 isolated from the leaf of Vanda cristata has the ability to colonize with roots of plants and protect the plant. PVL1 was isolated using laboratory synthetic media. 16S rRNA gene sequencing method has been employed for identification before and after root colonization ability.

Results

Original isolated and remunerated strain from colonized roots were identified as Bacillus spp. as per EzBiocloud database. The presence of bacteria in the root section of the plantlet was confirmed through Epifluorescence microscopy of colonized roots. The in-vitro plantlet colonized by PVL1 as well as DLMB attained higher growth than the control. PVL1 capable of producing plant beneficial phytohormone under in vitro cultivation. HPLC and GC-MS analysis suggest that colonized plants contain Indole Acetic Acid (IAA). The methanol extract of Bacillus spp., contains 0.015 μg in 1 μl concentration of IAA. PVL1 has the ability to produce antimicrobial compounds such as ethyl iso-allocholate, which exhibits immune restoring property. One-way ANOVA shows that results were statistically significant at P ≤ 0.05 level.

Conclusions

Hence, it has been concluded that Bacillus spp. PVL1 can promote plant growth through secretion of IAA during root colonization and ethyl iso-allocholate to protect plants from foreign infections. Thus, this study supports to support Koch’s postulates of bacteria establishment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00676-9.

IDENTIFICATION OF ENDOPHYTIC BACTERIA OF SEEDS FROM Cedrela odorata L. (Meliaceae) WITH BIOTECHNOLOGICAL CHARACTERISTICS

In the present study, 62 endophytic bacterial strains of cedar seeds (Cedrela odorataL.), collected in the municipalities of Huehuetán, Motozintla, and Pijijiapan in the state of Chiapas, Mexico were isolated. The goal was to identify characteristics of biotechnological interest such as biocontrol, promotion of plant growth, and growth in aromatic compounds. The strains were identified by the partial sequence of the 16S ribosomal gene as belonging to the Bacillusgenus. The biocontrol capacity of phytopathogenic fungi, production of indoleacetic acid (IAA), solubilization of phosphate, and growth in xenobiotic compounds (phenanthrene, benzene, anthracene, or phenol) were detected in 26 strains of the 62 isolates. 21 % of the strains inhibited the mycelial growth of Alternaria solaniand Fusariumsp., and 13 % of the Phytophthora capsicioomycete. IAA production was detected in 24 isolates, phosphate solubilizing activity was identified in 18 isolates, while the ability to grow in the presence of phenanthrene and benzene was found in 26 isolates; 24 isolates grew in the presence of anthracene and only two isolates grew in phenol as the only carbon sources. This is the first report of the isolation and identification of endophytic bacteria from cedar seeds, where biotechnological characteristics were detected for biological control, promotion of plant growth, and growth in the presence of xenobiotic compounds.

Bacteria from tropical semiarid temporary ponds promote maize growth under hydric stress

World climate change has triggered soil water stress and imposed limitations on agricultural production. Plant growth-promoting bacteria (PGPBs) have been an efficient strategy to improve the biological supply and growth of plants under distinct abiotic stress conditions. We hypothesized that the soils from a temporary pond may harbor PGPBs with potential strains which increase maize tolerance to water deficit. We studied rhizosphere and bulk soil of Mimosa bimucronata in a temporary pond from semiarid Northeast Brazil to access strains with characteristics to promote plant growth and mitigate abiotic stress for maize crop. We isolated 355 bacterial isolates, from which 96 were selected based on the morphophysiological characterization to assess IAA production (42 % produced over 50 μg mL^-1 of IAA), calcium phosphate solubilization (with one isolate achieving medium IS), biofilm and exopolysaccharides production (66 % and 98 % of isolates, respectively). Based on these mechanisms, the 30 most promising bacterial isolates were selected to assess biological nitrogen fixation (74 % of the isolates showed nitrogenase activity greater than 20 C₂H₄.h^-1.mg^-1), ACC deaminase activity (80 % of isolates) and growth in medium with reduced water activity (8 % of isolates grew in medium with water activity (A_w) of 0.844). We sequenced the 16S rRNA gene from the seven most promising isolates in in vitro and in vivo assays, which were identified as Staphylococcus edaphicus, Bacillus wiedmannii, Micrococcus yunnanensis, Streptomyces alboflavus, Streptomyces alboflavus, Bacillus wiedmanni and Bacillus cereus. In vivo, eleven isolates and three bacterial consortia did not differ from the control with nutrient solution, for total leaf area and root dry mass of maize. S. alboflavus (BS43) had the best in vivo results, not differing from the control with nutrient solution. We highlight the unpublished potential of Staphylococcus edaphicus and Streptomyces alboflavus in promoting the growth of plants under water stress. In addition, it is the first report of bacteria isolated from a temporary pond in the Brazilian semiarid which promoting plant growth attributes and development.

Endophytes: Colonization, Behaviour, and Their Role in Defense Mechanism

Biotic and abiotic factors cause an enormous amount of yield and economical loss. However, endophytes can play a significant role in enhancing the tolerance of plants. Endophytes systematically colonize different parts of the host, but plants use a variety of defense mechanisms towards microbial infection. However, they have to survive the oxidative environments, and endophytes like Enterobacter sp. encode superoxide dismutases, catalases, and hydroperoxide reductases to cope up the oxidative stress during colonization. On the contrary, others produce subtilomycin which binds with flagella to affect flg22-induced plant defense. The behavior of endophytes can be affected by different genes in hydrolase activity when they come into contact with the host plant. The lifestyle of endophytes is influenced by environmental factors, the host, and microbial genotypes, as well as an imbalance in nutrient exchange between the microbe and the host. For instance, induction of PiAMT1 in root endophyte Piriformospora indica indicates depletion of nitrogen which plays as a triggering factor for activation of the saprotrophic program. Microbes enhance disease resistance through induced systemic resistance (ISR), and Bacillus cereus triggers ISR against Botrytis cinerea through an accumulation of the PR1 protein and activates MAPK signaling and WRKY53 gene expression by the JA/ET signaling pathway. Similarly, Trichoderma arundinaceum produces trichodiene that affects Botrytis cinerea through induction of defense-related genes encoding salicylic acid (SA) and jasmonate (JA). Overall, endophytes can play a vital role in disease management.

Effect of Ammonia and Indole-3-acetic Acid Producing Endophytic Klebsiella pneumoniae YNA12 as a Bio-Herbicide for Weed Inhibition: Special Reference with Evening Primroses

Information on the use of endophytic bacteria as a bio-herbicide for the management of weed control in agricultural fields is limited. The current study aimed to isolate endophytic bacteria from evening primroses and to screen them for their bio-herbicidal activity. Two isolated endophytic bacteria (Pantoea dispersa YNA11 and Klebsiella pneumoniae YNA12) were initially screened for citrate utilization and for indole-3-acetic acid (IAA) and catalase production. The preliminary biochemical assessment showed YNA12 as a positive strain. Ammonia, catalase, and IAA in its culture filtrate were quantified. Gas Chromatography/Mass Spectroscopy- Selective Ion Monitoring (GC/MS-SIM) analysis revealed the production of IAA by YNA12 in a time-dependent manner. YNA12 also exhibited significant ammonia-producing potential and catalase activity against hydrogen peroxide. The YNA12 culture filtrate significantly inhibited the germination rate of evening primrose seeds, resulting in a marked reduction in seedling length and biomass compared with those of the control seeds. Moreover, the culture filtrate of YNA12 significantly accelerated the endogenous abscisic acid (ABA) production and catalase activity of evening primrose seedlings. Macronutrient regulation was adversely affected in the seedlings exposed to the culture filtrate of YNA12, leading to inhibition of seed germination. The current results suggest that endophytic YNA12 may be used as a potent bio-herbicidal agent for controlling weed growth and development.

Bacillus amyloliquefaciens RWL-1 as a New Potential Strain for Augmenting Biochemical and Nutritional Composition of Fermented Soybean

Soybean (Glycine max L.) is a good source of natural antioxidants and commonly consumed as fermented products such as cheonggukjang, miso, tempeh, and sufu in Asian countries. The aim of the current study was to examine the influence of novel endophytic bacterial strain, Bacillus amyloliquefaciens RWL-1 as a starter for soybean fermentation. During fermentation, the cooked soybeans were inoculated with different concentrations (1%, 3%, and 5%) of B. amyloliquefaciens RWL-1. The changes in 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activities, total phenolic contents, isoflavones (Daidzin, Genistin, Glycitin, Daidzein, Glycitein, and Genistein), amino acids (aspartic acid, threonine, serine, glutamic acid, glycine, alanine, cysteine, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine, and proline) composition, and minerals (calcium, copper, iron, potassium, magnesium, manganese, sodium, nickel, lead, arsenic, and zinc) were investigated. The level of antioxidants, total phenolic contents, isoflavones, and total amino acids were higher in fermented soybean inoculated with 1% B. amyloliquefaciens RWL-1 after 60 h of fermentation as compared to control, 3% and 5% B. amyloliquefaciens RWL-1. Additionally, fermented soybean inoculated with 5% B. amyloliquefaciens RWL-1 showed the highest values for mineral contents. Changes in antioxidant activities and bioactive compounds depended on the concentration of the strain used for fermentation. From these results, we conclude that fermented soybean has strong antioxidant activity, probably due to its increased total phenolic contents and aglycone isoflavone that resulted from fermentation. Such natural antioxidants could be used in drug and food industries and can be considered to alleviate oxidative stress.

Physiological Response of Cape Gooseberry Seedlings to Three Biological Control Agents Under Fusarium oxysporum f. sp. physali Infection

Cape gooseberry (Physalis peruviana) fruit has gained recognition owing to its nutritional value and versatility to be consumed processed or as a fresh product. These characteristics have made it an important product in both national and international markets. One of the main limitations for this crop is Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. physalis, for which biological control is emerging as an alternative to conventional management with chemical synthesis products. However, information on the effect that biological control agents have on the growth and development of plants is scarce. In this research, the physiological response of cape gooseberry plants (stomatal conductance, leaf water potential, growth parameters, total chlorophyll, carotenoid, and proline and malondialdehyde contents) to the treatment with three potential biocontrol agents (BCAs) Trichoderma koningiopsis, Trichoderma virens, and Bacillus velezensis was determined. The study was conducted under greenhouse conditions; F. oxysporum was inoculated in the soil, and BCAs were soil drenched in the germination and transplanting stages. Plants inoculated with the pathogen and plants without inoculation were used as controls. It was found that the plants inoculated and treated with T. virens showed the lowest disease levels (area under the disease progress curve of 48.5 and disease severity index of 2.1). Additionally, they showed a lower water potential (-0.317 Mpa), a greater leaf area (694.7 cm²), and a higher stomatal conductance (110.3 mmol m^-2 s^-1) compared with the control. Consequently, it can be concluded that T. virens can be a good candidate for the management of Fusarium wilt in the cape gooseberry crop.

Genome Sequences of Brevundimonas naejangsanensis Strain FS1091 and Bacillus amyloliquefaciens Strain FS1092, Isolated from a Fresh-Cut-Produce-Processing Plant

The complete genome sequences of Brevundimonas naejangsanensis strain FS1091 and Bacillus amyloliquefaciens strain FS1092, which were isolated from a commercial fresh-cut-produce-processing facility, were determined. Both FS1091 and FS1092 have one circular chromosome of approximately 3.15 and 4.24 Mb, respectively.

The complete genome sequences of Brevundimonas naejangsanensis strain FS1091 and Bacillus amyloliquefaciens strain FS1092, which were isolated from a commercial fresh-cut-produce-processing facility, were determined. Both FS1091 and FS1092 have one circular chromosome of approximately 3.15 and 4.24 Mb, respectively.

Amelioration of heavy metal stress by endophytic Bacillus amyloliquefaciens RWL-1 in rice by regulating metabolic changes: potential for bacterial bioremediation

This study aimed to investigate the bioremediation efficiency of phytohormone-producing endophytic Bacillus amyloliquefaciens RWL-1 isolated from rice seeds. In this study, we tested RWL-1 against various heavy metals (Cu, Cr, Pb, and Cd). Among the tested heavy metals, RWL-1 showed the highest tolerance for Cu stress and we observed alterations in growth kinetics with various Cu concentrations (1, 2.5, and 5 mM). We confirmed the biosorption potential of RWL-1 by scanning electron microscopy coupled with energy-dispersive X-ray spectrometry showing that Cu ions were adsorbed on RWL-1 cell surfaces. We further tested RWL-1 for its plant growth promoting and stress reliance efficiency in response to a dose-dependent increase in soil Cu (1, 2.5, and 5 mM). The RWL-1 inoculation significantly increased seedling biomass and growth attributes compared with non-inoculated control seedlings with and without Cu stress. Moreover, RWL-1 inoculation significantly promoted a physiochemical response in seedlings with and without Cu stress by reducing Cu uptake, improving carbohydrate levels (glucose, sucrose, fructose, and raffinose), enhancing amino acids regulation, and augmenting antioxidant levels (POD, PPO, and GHS). Levels of stress-responsive phytohormones such as abscisic acid (ABA) and jasmonic acid were significantly reduced in RWL-1-inoculated seedlings as compared with non-inoculated control seedlings under normal condition and same levels of Cu stress. In conclusion, the inoculation of B. amyloliquefaciens RWL-1 can significantly improve plant growth in Cu-contaminated soil and reduce metal accumulation, thus making plants safer for consumption. This approach could be tremendously helpful for safe and sustainable agriculture in heavy metal-contaminated areas.

Fusarium oxysporum f. sp. lycopersici causal agent of vascular wilt disease of tomato: Biology to diversity- A review

Tomato (Lycopersicon esculentum) is one of the widely grown vegetables worldwide. Fusarium oxysporum f. sp. lycopersici (FOL) is the significant contributory pathogen of tomato vascular wilt. The initial symptoms of the disease appear in the lower leaves gradually, trail by wilting of the plants. It has been reported that FOL penetrates the tomato plant, colonizing and leaving the vascular tissue dark brown, and this discoloration extends to the apex, leading to the plants wilting, collapsing and dying. Therefore, it has been widely accepted that wilting caused by this fungus is the result of a combination of various physiological activities, including the accumulation of fungal mycelia in and around xylem, mycotoxin production, inactivation of host defense, and the production of tyloses; however, wilting symptoms are variable. Therefore, the selection of molecular markers may be a more effective means of screening tomato races. Several studies on the detection of FOL have been carried out and have suggested the potency of the technique for diagnosing FOL. This review focuses on biology and variability of FOL, understanding and presenting a holistic picture of the vascular wilt disease of tomato in relation to disease model, biology, virulence. We conclude that genomic and proteomic approachesare greater tools for identification of informative candidates involved in pathogenicity, which can be considered as one of the approaches in managing the disease.

Co-inoculation of Bacillus sp. and Pseudomonas putida at different development stages acts as a biostimulant to promote growth, yield and nutrient uptake of tomato

AIMS

This study builds upon the premise that roots culture distinct bacteria at specific stages of plant growth to benefit of specific microbial services needed at that particular growth stage. Accordingly, we hypothesized that the co-inoculation of beneficial microbes with distinct properties at specific stages of plant development would enhance plant performance.

METHODS AND RESULTS

The chosen microbes were Bacillus pumilus, Bacillus amyloliquefaciens, Bacillus mojavensis and Pseudomonas putida. These microbes were selected based on their specific services ranging from nutrient solubilization, root growth promotion and disease resistance, and were applied to the roots of tomato plants at specific time points when those services were needed the most by the plant. Laboratory and greenhouse studies were conducted to evaluate the effects of co-inoculation at specific stages of development compared to single microbial applications.

CONCLUSION

In general, the combination of three microbes gave the highest biomass and yield without the presence of disease. Applications of three microbes showed the highest root/shoot ratio, and applications of four microbes the lowest ratio. Pseudomonas putida significantly increased fruit macronutrient and micronutrient contents.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our studies suggest that co-inoculation of three or four microbes is a good strategy for healthy crop production.

Indole-3-acetic-acid and ACC deaminase producing Leclercia adecarboxylata MO1 improves Solanum lycopersicum L. growth and salinity stress tolerance by endogenous secondary metabolites regulation

BACKGROUND

The utilization of plant growth-promoting microbes is an environment friendly strategy to counteract stressful condition and encourage plants tolerance. In this regards, the current study was designed to isolate ACC deaminase and indole-3-acetic acid (IAA) producing halotolerant bacteria to promote tomato (Solanum lycopersicum L.) growth and tolerance against salinity stress.

RESULTS

The selected bacterial isolate MO1 was identified as Leclercia adecarboxylata and IAA quantification results revealed that MO1 produced significant amount of IAA (9.815 ± 0.6293 μg mL- 1). The MO1 showed the presence of ACC (1-Aminocyclopropane-1-Carboxylate) deaminase responsible acdS gene and tolerance against salinity stress. A plant microbe interaction experiment using tomato (Solanum lycopersicum L.) with glycine betaine (GB) as a positive control was carried out to investigate the positive role MO1 in improving plant growth and stress tolerance. The results indicated that MO1 inoculation and GB application significantly increased growth attributes under normal as well as saline condition (120 mM NaCl). The MO1 inoculation and GB treatment approach conferred good protection against salinity stress by significantly improving glucose by 17.57 and 18.76%, sucrose by 34.2 and 12.49%, fructose by 19.9 and 10.9%, citric acid by 47.48 and 34.57%, malic acid by 52.19 and 28.38%, serine by 43.78 and 69.42%, glycine by 14.48 and 22.76%, methionine by 100 and 124.99%, threonine by 70 and 63.08%, and proline by 36.92 and 48.38%, respectively, while under normal conditions MO1 inoculation and GB treatment also enhanced glucose by 19.83 and 13.19%, sucrose by 23.43 and 15.75%, fructose by 15.79 and 8.18%, citric acid by 43.26 and 33.14%, malic acid by 36.18 and 14.48%, serine by 46.5 and 48.55%, glycine by 19.85 and 29.77%, methionine by 22.22 and 38.89%, threonine by 21.95 and 17.07%, and proline by 29.61 and 34.68% compared to levels in non-treated plants, respectively. In addition, the endogenous abscisic acid (ABA) level was noticeably lower in MO1-inoculated (30.28 and 30.04%) and GB-treated plants (45 and 35.35%) compared to their corresponding control plants under normal condition as well as salinity stress, respectively.

CONCLUSION

The current findings suggest that the IAA- and ACC-deaminase-producing abilities MO1 can improve plants tolerance to salinity stress.

Metabolic and proteomic alteration in phytohormone-producing endophytic Bacillus amyloliquefaciens RWL-1 during methanol utilization

INTRODUCTION

Methanol utilization by bacteria is important for various industrial processes. Methylotrophic bacteria are taxonomically diverse and some species promote plant growth and induce stress tolerance. However, methylotrophic potential of bacterial endophytes is poorly understood.

OBJECTIVE

The current study aimed to evaluate the metabolomic and proteomic changes in endophytic Bacillus amyloliquefaciens RWL-1 caused by its methanol utilization and the resultant influence on its phytohormone production.

METHODS

B. amyloliquefaciens RWL-1 was grown in LB medium with different concentrations [0 (control), 0.5, 1, 1.5, 2, 2.5, 3, 3.5, and 4%) of methanol to examine its methylotrophic potential. SDS-PAGE analysis was carried out for bacterial protein confirmation. Moreover, the phytohormones (indole 3 acetic acid (IAA), gibberellins (GAs), abscisic acid (ABA)) produced by RWL-1 in methanol supplemented medium were quantified by GC-MS/SIM (6890N Network GC system, and 5973 Network Mass Selective Detector; Agilent Technologies, Santa Clara, CA, USA), while the antioxidants were estimated spectrophotometrically (T60 UV-VIS spectrophotometer, Leicester, UK). The amino acid quantification was carried out by amino acid analyzer (HITACHI L-8900, Japan). Furthermore, Nano-liquid chromatography (LC)-MS/MS analysis was performed with an Agilent system (Wilmington, DE, USA) for proteomic analysis while mascot algorithm (Matrix science, USA) was used to identify peptide sequences present in the protein sequence database.

RESULTS

RWL-1 showed significant growth in media supplemented with 2 and 3.5% methanol, when compared with other concentrations. Mass spectroscopy analysis revealed that RWL-1 utilizes methanol efficiently as a carbon source. In the presence of methanol, RWL-1 produced significantly higher levels of IAA but lower levels of ABA, when compared with the control. Further, enzymatic antioxidants and functional amino acids were significantly up-regulated, with predominant expression of glutamic acid and alanine. Nano-liquid chromatography, quadrupole time-of-flight analysis, and quantitative analysis of methanol-treated bacterial cells showed expression of eight different types of proteins, including detoxification proteins, unrecognized and unclassified enzymes with antioxidant properties, proteases, metabolism enzymes, ribosomal proteins, antioxidant proteins, chaperones, and heat shock proteins.

CONCLUSION

Results demonstrate that RWL-1 can significantly enhance its growth by utilizing methanol, and could produce phytohormones when growing in methanol-supplemented media, with increased expression of specific proteins and different biochemicals. These results will be useful in devising strategies for utilizing methylotrophic bacterial endophytes as alternative promoters of plant growth. Understanding RWL-1 ability to utilize methanol. The survival and phytohormones production by Bacillus amyloliquefaciens RWL-1 in methanol supplemented media whistle inducing metabolic and proteomic changes.

Mechanisms of Cr(VI) resistance by endophytic Sphingomonas sp. LK11 and its Cr(VI) phytotoxic mitigating effects in soybean (Glycine max L.)

Chromium Cr(VI) is highly toxic and leads to impaired phenotypic plasticity of economically important crops. The current study assessed an endophytic-bacteria assisted metal bio-remediation strategy to understand stress-alleviating mechanisms in Glycine max L (soybean) plants inoculated with Sphingomonas sp. LK11 under severe Cr(VI) toxicity. The screening analysis showed that high Cr concentrations (5.0 mM) slightly suppressed LK11 growth and metal uptake by LK11 cells, while significantly enhancing indole-3-acetic acid (IAA) production. Endophytic LK11 significantly upregulated its antioxidant system compared to control by enhancing reduced glutathione (GSH), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities to counteract Cr-induced oxidative stress. Cr toxicity induced cell morphological alteration, as shown by SEM-EDX analysis and triggered significant lipid peroxidation. The interaction between LK11 and soybean in Cr-contaminated soil significantly increased plant growth attributes and down-regulated the synthesis of endogenous defense-related phytohormones, salicylic acid and abscisic acid, by 20% and 37%, respectively, and reduced Cr translocation to the roots, shoot, and leaves. Additionally, Cr-induced oxidative stress was significantly reduced in LK11-inoculated soybean, regulating metal responsive reduced GSH and enzymatic antioxidant CAT. Current findings indicate that LK11 may be a suitable candidate for the bioremediation of Cr-contaminated soil and stimulation of host physiological homeostasis.

Antifungal Activity of Bacillus Species Against Fusarium and Analysis of the Potential Mechanisms Used in Biocontrol

Fusarium is a complex genus of ascomycete fungi that consists of plant pathogens of agricultural relevance. Controlling Fusarium infection in crops that leads to substantial yield losses is challenging. These economic losses along with environmental and human health concerns over the usage of chemicals in attaining disease control are shifting focus toward the use of biocontrol agents for effective control of phytopathogenic Fusarium spp. In the present study, an analysis of the plant-growth promoting (PGP) and biocontrol attributes of four bacilli (Bacillus simplex 30N-5, B. simplex 11, B. simplex 237, and B. subtilis 30VD-1) has been conducted. The production of cellulase, xylanase, pectinase, and chitinase in functional assays was studied, followed by in silico gene analysis of the PGP-related and biocontrol-associated genes. Of all the bacilli included in this study, B. subtilis 30VD-1 (30VD-1) demonstrated the most effective antagonism against Fusarium spp. under in vitro conditions. Additionally, 100 μg/ml of the crude 1-butanol extract of 30VD-1’s cell-free culture filtrate caused about 40% inhibition in radial growth of Fusarium spp. Pea seed bacterization with 30VD-1 led to considerable reduction in wilt severity in plants with about 35% increase in dry plant biomass over uninoculated plants growing in Fusarium-infested soil. Phase contrast microscopy demonstrated distortions and abnormal swellings in F. oxysporum hyphae on co-culturing with 30VD-1. The results suggest a multivariate mode of antagonism of 30VD-1 against phytopathogenic Fusarium spp., by producing chitinase, volatiles, and other antifungal molecules, the characterization of which is underway.

Complete genome sequencing and analysis of endophytic Sphingomonas sp. LK11 and its potential in plant growth

Our study aimed to elucidate the plant growth-promoting characteristics and the structure and composition of Sphingomonas sp. LK11 genome using the single molecule real-time (SMRT) sequencing technology of Pacific Biosciences. The results revealed that LK11 produces different types of gibberellins (GAs) in pure culture and significantly improves soybean plant growth by influencing endogenous GAs compared with non-inoculated control plants. Detailed genomic analyses revealed that the Sphingomonas sp. LK11 genome consists of a circular chromosome (3.78 Mbp; 66.2% G+C content) and two circular plasmids (122,975 bps and 34,160 bps; 63 and 65% G+C content, respectively). Annotation showed that the LK11 genome consists of 3656 protein-coding genes, 59 tRNAs, and 4 complete rRNA operons. Functional analyses predicted that LK11 encodes genes for phosphate solubilization and nitrate/nitrite ammonification, which are beneficial for promoting plant growth. Genes for production of catalases, superoxide dismutase, and peroxidases that confer resistance to oxidative stress in plants were also identified in LK11. Moreover, genes for trehalose and glycine betaine biosynthesis were also found in LK11 genome. Similarly, Sphingomonas spp. analysis revealed an open pan-genome and a total of 8507 genes were identified in the Sphingomonas spp. pan-genome and about 1356 orthologous genes were found to comprise the core genome. However, the number of genomes analyzed was not enough to describe complete gene sets. Our findings indicated that the genetic makeup of Sphingomonas sp. LK11 can be utilized as an eco-friendly bioresource for cleaning contaminated sites and promoting growth of plants confronted with environmental perturbations.

Endophyte-Mediated Modulation of Defense-Related Genes and Systemic Resistance in Withania somnifera (L.) Dunal under Alternaria alternata Stress

Endophytes have been explored and found to perform an important role in plant health. However, their effects on the host physiological function and disease management remain elusive. The present study aimed to assess the potential effects of endophytes, singly as well as in combination, in Withania somnifera (L.) Dunal, on various physiological parameters and systemic defense mechanisms against Alternaria alternata Seeds primed with the endophytic bacteria Bacillus amyloliquefaciens and Pseudomonas fluorescens individually and in combination demonstrated an enhanced vigor index and germination rate. Interestingly, plants treated with the two-microbe combination showed the lowest plant mortality rate (28%) under A. alternata stress. Physiological profiling of treated plants showed improved photosynthesis, respiration, transpiration, and stomatal conductance under pathogenic stress. Additionally, these endophytes not only augmented defense enzymes and antioxidant activity in treated plants but also enhanced the expression of salicylic acid- and jasmonic acid-responsive genes in the stressed plants. Reductions in reactive oxygen species (ROS) and reactive nitrogen species (RNS) along with enhanced callose deposition in host plant leaves corroborated well with the above findings. Altogether, the study provides novel insights into the underlying mechanisms behind the tripartite interaction of endophyte-A. alternata-W. somnifera and underscores their ability to boost plant health under pathogen stress.IMPORTANCEW. somnifera is well known for producing several medicinally important secondary metabolites. These secondary metabolites are required by various pharmaceutical sectors to produce life-saving drugs. However, the cultivation of W. somnifera faces severe challenge from leaf spot disease caused by A. alternata To keep pace with the rising demand for this plant and considering its capacity for cultivation under field conditions, the present study was undertaken to develop approaches to enhance production of W. somnifera through intervention using endophytes. Application of bacterial endophytes not only suppresses the pathogenicity of A. alternata but also mitigates excessive ROS/RNS generation via enhanced physiological processes and antioxidant machinery. Expression profiling of plant defense-related genes further validates the efficacy of bacterial endophytes against leaf spot disease.

Rhizospheric microbial communities are driven by Panax ginseng at different growth stages and biocontrol bacteria alleviates replanting mortality

The cultivation of Panax plants is hindered by replanting problems, which may be caused by plant-driven changes in the soil microbial community. Inoculation with microbial antagonists may efficiently alleviate replanting issues. Through high-throughput sequencing, this study revealed that bacterial diversity decreased, whereas fungal diversity increased, in the rhizosphere soils of adult ginseng plants at the root growth stage under different ages. Few microbial community, such as Luteolibacter, Cytophagaceae, Luteibacter, Sphingomonas, Sphingomonadaceae, and Zygomycota, were observed; the relative abundance of microorganisms, namely, Brevundimonas, Enterobacteriaceae, Pandoraea, Cantharellales, Dendryphion, Fusarium, and Chytridiomycota, increased in the soils of adult ginseng plants compared with those in the soils of 2-year-old seedlings. Bacillus subtilis 50-1, a microbial antagonist against the pathogenic Fusarium oxysporum, was isolated through a dual culture technique. These bacteria acted with a biocontrol efficacy of 67.8%. The ginseng death rate and Fusarium abundance decreased by 63.3% and 46.1%, respectively, after inoculation with B. subtilis 50-1. Data revealed that microecological degradation could result from ginseng-driven changes in rhizospheric microbial communities; these changes are associated with the different ages and developmental stages of ginseng plants. Biocontrol using microbial antagonists alleviated the replanting problem.