Plant Development of Early-Maturing Spring Wheat (Triticum aestivum L.) under Inoculation with Bacillus sp. V2026

Root colonization dynamics of alginate encapsulated rhizobacteria: implications for Arabidopsis thaliana root growth and durum wheat performance

Bioencapsulation in alginate capsules offers an interesting opportunity for the efficient delivery of microbial inoculants for agricultural purposes. The present study evaluated the ionic gelation technique to prepare beads loaded with two plant growth-promoting bacteria (PGPB), Bacillus thuringiensis strain B25 and Pantoea agglomerans strain Pa in 1% alginate supplemented with 5mM proline as an osmoprotectant. Capsule morphology, survival rate, encapsulation efficiency, and viability during 24 months of storage as well as the stability of PGP activities were studied. Our results indicate that more than 99% of bacteria were effectively trapped in the alginate beads, which successfully released live bacteria after 60 days of storage at room temperature. A considerable survival of B. thuringiensis B25 throughout the storage period was detected, while the inoculated concentration of 8.72 × 109 (±0.04 ×109) CFU/mL was reduced to 99.9% for P. agglomerans Pa after 24 months of storage. Notably, a higher survival of individually encapsulated bacteria was observed compared to their co-inoculation. The colonization capacity of model plant Arabidopsis thaliana roots by free and encapsulated bacteria was detected by the triphenyltetrazolium chloride test. Moreover, both strains effectively colonized the rhizosphere, rhizoplane, and endosphere of durum wheat plants and exerted a remarkable improvement in plant growth, estimated as a significant increase in the quantities of total proteins, sugars, and chlorophyll pigments, besides roots and shoots length. This study demonstrated that alginate-encapsulated B. thuringiensis B25 and P. agglomerans Pa could be used as inoculants in agriculture, as their encapsulation ensures robust protection, maintenance of viability and PGP activity, and controlled bacterial biostimulant release into the rhizosphere.

PGPB Isolated from Drought-Tolerant Plants Help Wheat Plants to Overcome Osmotic Stress

The aim of this research was to study the effect of plant-growth-promoting bacteria (PGPB) isolated from the drought-tolerant plants camel thorn (Alhagi pseudoalhagi (M.Bieb.) Fisch) and white pigweed (Chenopodium album L.) on wheat (Triticum aestivum L.) plants cv. Lenigradskaya 6, growing under hydroponic conditions and osmotic stress (generated by 12% polyethylene glycol-6000 (PEG)). Based on the assumption that plants create a unique microbiome that helps them overcome various stresses, we hypothesized that bacteria isolated from drought-tolerant plants may assist cultivated wheat plants in coping with drought stress. PGPB were isolated from seeds and leaves of plants and identified as Bacillus spp. (strains Cap 07D, Cap 09D, and App 11D); Paenibacillus sp. (Cap 286); and Arthrobacter sp. (Cap 03D). All bacteria produced different phytohormones such as indole acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GAS3) and were capable of stimulating wheat growth under normal and osmotic stress conditions. All PGPB reduced the malondialdehyde (MDA) content, increased the total chlorophyll content by increasing chlorophyll a, and modulated wheat hormone homeostasis and CAT and POX activities under osmotic conditions. Selected strains can be promising candidates for the mitigating of the drought stress of wheat plants.

Progress in Microbial Fertilizer Regulation of Crop Growth and Soil Remediation Research

More food is needed to meet the demand of the global population, which is growing continuously. Chemical fertilizers have been used for a long time to increase crop yields, and may have negative effect on human health and the agricultural environment. In order to make ongoing agricultural development more sustainable, the use of chemical fertilizers will likely have to be reduced. Microbial fertilizer is a kind of nutrient-rich and environmentally friendly biological fertilizer made from plant growth-promoting bacteria (PGPR). Microbial fertilizers can regulate soil nutrient dynamics and promote soil nutrient cycling by improving soil microbial community changes. This process helps restore the soil ecosystem, which in turn promotes nutrient uptake, regulates crop growth, and enhances crop resistance to biotic and abiotic stresses. This paper reviews the classification of microbial fertilizers and their function in regulating crop growth, nitrogen fixation, phosphorus, potassium solubilization, and the production of phytohormones. We also summarize the role of PGPR in helping crops against biotic and abiotic stresses. Finally, we discuss the function and the mechanism of applying microbial fertilizers in soil remediation. This review helps us understand the research progress of microbial fertilizer and provides new perspectives regarding the future development of microbial agent in sustainable agriculture.

Phytohormone Production by the Endophyte Bacillus safensis TS3 Increases Plant Yield and Alleviates Salt Stress

Endophytic bacteria can be used to overcome the effect of salinity stress and promote plant growth and nutrient uptake. Bacillus safensis colonizes a wide range of habitats due to survival in extreme environments and unique physiological characteristics, such as a high tolerance for salt, heavy metals, and ultraviolet and gamma radiations. The aim of our study was to examine the salt resistance of the endophytic strain TS3 B. safensis and its ability to produce phytohormones and verify its effect on plant yield in field trials and the alleviation of salt stress in pot experiments. We demonstrate that the strain TS3 is capable of producing enzymes and phytohormones such as IAA, ABA and tZ. In pot experiments with radish and oat plants in salinization, the strain TS3 contributed to the partial removal of the negative effect of salinization. The compensatory effect of the strain TS3 on radish plants during salinization was 46.7%, and for oats, it was 108%. We suppose that such a pronounced effect on the plants grown and the salt stress is connected with its ability to produce phytohormones. Genome analysis of the strain TS3 showed the presence of the necessary genes for the synthesis of compounds responsible for the alleviation of the salt stress. Strain B. safensis TS3 can be considered a promising candidate for developing biofertilizer to alleviate salt stress and increase plant yield.

Biocontrol of fungal phytopathogens by Bacillus pumilus

Plant growth-promoting bacteria are one of the most interesting methods of controlling fungal phytopathogens. These bacteria can participate in biocontrol via a variety of mechanisms including lipopeptide production, hydrolytic enzymes (e.g., chitinase, cellulases, glucanase) production, microbial volatile organic compounds (mVOCs) production, and induced systemic resistance (ISR) triggering. Among the bacterial genera most frequently studied in this aspect are Bacillus spp. including Bacillus pumilus. Due to the range of biocontrol traits, B. pumilus is one of the most interesting members of Bacillus spp. that can be used in the biocontrol of fungal phytopathogens. So far, a number of B. pumilus strains that exhibit biocontrol properties against fungal phytopathogens have been described, e.g., B. pumilus HR10, PTB180, B. pumilus SS-10.7, B. pumilus MCB-7, B. pumilus INR7, B. pumilus SE52, SE34, SE49, B. pumilus RST25, B. pumilus JK-SX001, and B. pumilus KUDC1732. B. pumilus strains are capable of suppressing phytopathogens such as Arthrobotrys conoides, Fusarium solani, Fusarium oxysporum, Sclerotinia sclerotiorum, Rhizoctonia solani, and Fagopyrum esculentum. Importantly, B. pumilus can promote plant growth regardless of whether it alters the native microbiota or not. However, in order to increase its efficacy, research is still needed to clarify the relationship between the native microbiota and B. pumilus. Despite that, it can already be concluded that B. pumilus strains are good candidates to be environmentally friendly and commercially effective biocontrol agents.

Bacillus paralicheniformis RP01 Enhances the Expression of Growth-Related Genes in Cotton and Promotes Plant Growth by Altering Microbiota inside and outside the Root

Plant growth-promoting bacteria (PGPB) can promote plant growth in various ways, allowing PGPB to replace chemical fertilizers to avoid environmental pollution. PGPB is also used for bioremediation and in plant pathogen control. The isolation and evaluation of PGPB are essential not only for practical applications, but also for basic research. Currently, the known PGPB strains are limited, and their functions are not fully understood. Therefore, the growth-promoting mechanism needs to be further explored and improved. The Bacillus paralicheniformis RP01 strain with beneficial growth-promoting activity was screened from the root surface of Brassica chinensis using a phosphate-solubilizing medium. RP01 inoculation significantly increased plant root length and brassinosteroid content and upregulated the expression of growth-related genes. Simultaneously, it increased the number of beneficial bacteria that promoted plant growth and reduced the number of detrimental bacteria. The genome annotation findings also revealed that RP01 possesses a variety of growth-promoting mechanisms and a tremendous growth-promoting potential. This study isolated a highly potential PGPB and elucidated its possible direct and indirect growth-promoting mechanisms. Our study results will help enrich the PGPB library and provide a reference for plant-microbe interactions.

Bioremediation of Heavy Metals by the Genus Bacillus

Environmental contamination with heavy metals is one of the major problems caused by human activity. Bioremediation is an effective and eco-friendly approach that can reduce heavy metal contamination in the environment. Bioremediation agents include bacteria of the genus Bacillus, among others. The best-described species in terms of the bioremediation potential of Bacillus spp. Are B. subtilis, B. cereus, or B. thuringiensis. This bacterial genus has several bioremediation strategies, including biosorption, extracellular polymeric substance (EPS)-mediated biosorption, bioaccumulation, or bioprecipitation. Due to the above-mentioned strategies, Bacillus spp. strains can reduce the amounts of metals such as lead, cadmium, mercury, chromium, arsenic or nickel in the environment. Moreover, strains of the genus Bacillus can also assist phytoremediation by stimulating plant growth and bioaccumulation of heavy metals in the soil. Therefore, Bacillus spp. is one of the best sustainable solutions for reducing heavy metals from various environments, especially soil.

Biocontrol potential and action mechanism of Bacillus amyloliquefaciens DB2 on Bipolaris sorokiniana

Introduction

Bipolaris sorokiniana is the popular pathogenic fungi fungus which lead to common root rot and leaf spot on wheat. Generally, chemical fungicides are used to control diseases. However, the environmental pollution resulting from fungicides should not be ignored. It is important to study the mode of antagonistic action between biocontrol microbes and plant pathogens to design efficient biocontrol strategies.

Results

An antagonistic bacterium DB2 was isolated and identified as Bacillus amyloliquefaciens. The inhibition rate of cell-free culture filtrate (CF, 20%, v/v) of DB2 against B. sorokiniana reached 92.67%. Light microscopy and scanning electron microscopy (SEM) showed that the CF significantly altered the mycelial morphology of B. sorokiniana and disrupted cellular integrity. Fluorescence microscopy showed that culture filtrate destroyed mycelial cell membrane integrity, decreased the mitochondrial transmembrane potential, induced reactive oxygen species (ROS) accumulation, and nuclear damage which caused cell death in B. sorokiniana. Moreover, the strain exhibited considerable production of protease and amylase, and showed a significant siderophore and indole-3-acetic acid (IAA) production. In the detached leaves and potted plants control assay, B. amyloliquefacien DB2 had remarkable inhibition activity against B. sorokiniana and the pot control efficacy was 75.22%. Furthermore, DB2 suspension had a significant promotion for wheat seedlings growth.

Conclusion

B. amyloliquefaciens DB2 can be taken as a potential biocontrol agent to inhibit B. sorokiniana on wheat and promote wheat growth.

Potential of Bacillus pumilus to directly promote plant growth

Plant Growth-Promoting Bacteria (PGPB) are a promising alternative to conventional fertilization. One of the most interesting PGPB strains, among the spore-forming bacteria of the phylum Firmicutes, is Bacillus pumilus. It is a bacterial species that inhabits a wide range of environments and shows resistance to abiotic stresses. So far, several PGPB strains of B. pumilus have been described, including B. pumilus LZP02, B. pumilus JPVS11, B. pumilus TUAT-1, B. pumilus TRS-3, and B. pumilus EU927414. These strains have been shown to produce a wide range of phytohormones and other plant growth-promoting substances. Therefore, they can affect various plant properties, including biometric traits, substance content (amino acids, proteins, fatty acids), and oxidative enzymes. Importantly, based on a study with B. pumilus WP8, it can be concluded that this bacterial species stimulates plant growth when the native microbiota of the inoculated soil is altered. However, there is still a lack of research with deeper insights into the structure of the native microbial community (after B. pumilus application), which would provide a better understanding of the functioning of this bacterial species in the soil and thus increase its effectiveness in promoting plant growth.