Bacillus subtilis and Bacillus licheniformis promote tomato growth

Screening of plant growth-promoting rhizobacteria and their growth-promoting activities for Stipa purpurea in alpine grassland

AIMS

Stipa purpurea is one of the dominant grass species in alpine grassland and plays a crucial role in safeguarding the ecosystem and restoring degraded grassland. To enhance the population dominance of S. purpurea and effectively prevent further grassland degradation. In this study, we screened high-efficiency plant growth-promoting rhizobacteria (PGPR) from rhizosphere soil samples, with the aim of improving the growth activity of S. purpurea through spraying PGPR.

METHODS AND RESULTS

We selected functional medium for the isolation of PGPR from the rhizosphere soils of five distinct sampling sites in the alpine grasslands surrounding Qinghai Lake. Nitrogenase activity, phosphorus-solubilization, carbon-fixation, indole acetic acid (IAA)-like compounds production, and 1-aminocyclopropane-1-carboxylate deaminase production were used to assess the growth-promoting capability of the PGPR. Additionally, the ecological adaptability of PGPR was examined. Finally, the growth promotion effect of high-efficiency PGPR on S. purpurea was determined using pot experiments. The results of this study showed that 136 strains were isolated and were categorized into 18 genera based on the 16S rRNA sequences. Among these, seven strains exhibited multiple characteristics of promoting growth, and meanwhile, strains GD-1-1, YD-2-4, GD-3-9, and HD-1-1 exhibited strong resistance to drought, cold, UV, and oxidation. The strains GD-1-1 and YD-2-4 had growth-promoting effects on the growth of S. purpurea, which significantly enhance the seed germination rate, facilitate the growth of the above-ground part of seedlings, and the formation of lateral roots. Additionally, the results of the principal component analysis indicated that the interaction effect of high-efficiency PGPRs with young roots was more beneficial than that with young sprout.

CONCLUSIONS

The results of this study provide outstanding strain resources and a theoretical foundation for the restoration of alpine degraded grassland. The findings further provide the basis for research and development of microbial fertilizer.

Effects of Rhizobacteria Strains on Plant Growth Promotion in Tomatoes (Solanum lycopersicum)

Numerous factors, such as soil fertility, climatic conditions, human activity, pests, and diseases, limit agricultural yields. Pesticides and fertilizers have become indispensable tools to satisfy the global food demand. However, its adverse environmental effects have led to the search for more sustainable and ethical techniques. Biofertilizers and biopesticides based on plant- growth-promoting rhizobacteria (PGPRs) are efficient and ecological treatments that promote plant growth and protection against pathogens and abiotic stresses. In this study, twelve rhizobacterial strains with plant-growth-promoting attributes were selected to evaluate their plant-growth-promoting effect on tomato plants (Solanum lycopersicum L. var Robin). Soil inoculation with these strains resulted in a significant increase in shoot length, up to 50% when compared with control plants. Regarding fresh biomass, rhizobacterial treatments significantly improved seedlings' fresh aerial weight with a maximum increase of 77%. Root biomass also demonstrated a substantial improvement, yielding 62.26% greater fresh root weight compared to the control. Finally, dry root weights exhibited the most remarkable enhancements, with values between 49 and 124%, when compared to the control plants. Concerning the nutritional status, the strains inoculation increased the macronutrients and micronutrients content in the aerial and root parts of the plants. All these findings suggest that rhizobacteria from different ecosystems and agriculture soils of the Canary Islands could be used as fertilizer inoculants to increase crop yield and promote more sustainable practices in modern agriculture.

Microencapsulated Microbial Seed Coating Could Improve Soil Environment and Maize Grain Yield in Saline Soil

Soil salinization is one of the major challenges for modern agriculture, posing a great threat to soil health and food security. Field experiments were conducted to evaluate the effect of seed coating on soil environment and maize growth in saline soils. Three treatments were applied to maize seeds: coating with a microencapsulated microbial agent (ME), coating with microbial only (MB), and no coating (CK). High-throughput sequencing of soil bacterial and fungal 16S and ITS rRNA genes was performed using the Illumina HiSeq platform to analyze the effects of these treatments on soil bacterial and fungal diversity and community structure. Additionally, the influence of different treatments on endogenous hormones and yield of maize were investigated. It was found that the coating with a microencapsulated microbial agent led to decreases in pH and electrical conductivity (EC), while increasing the content of soil available phosphorus. This coating improved soil microbial diversity, significantly increasing the relative abundance of the main bacteria genera, Bacillus (34.9%), and the main fungal genera, Mortierella (190.4%). The treatment also significantly enhanced indole-3-acetic acid (IAA) by 51.2%, contributing to improvements in resistance to salt stress. The germination rate increased by 22.9%, the 100-grain weight increased by 12.7%, and grain yield increased by 14.3%. The use of the microencapsulated microbial agent effectively mitigated the adverse effects of salt stress on maize plants. This approach is beneficial for promoting sustainable agriculture in saline soils.

Microbe-aided thermophilic composting accelerates manure fermentation

Aerobic composting is a key strategy to the sustainable use of livestock manure, which is however constrained by the slow kinetics. Microbe-aided thermophilic composting provides an attractive solution to this problem. In this study, we identified key thermophilic bacteria capable of accelerating manure composting based on the deciphering of manure bacterial community evolution in a thermophilic system. High-throughput sequencing showed a significant evolution of manure bacterial community structure with the increasing heating temperature. Firmicutes were substantially enriched by the heating, particularly some known thermotolerant bacterial species, such as Novibacillus thermophiles, Bacillus thermolactis, and Ammoniibacillus agariperforans. Correspondingly, through function prediction, we found bacterial taxa with cellulolytic and xylanolytic activities were significantly higher in the thermophilic process relative to the initial stage. Subsequently, a total of 47 bacteria were isolated in situ and their phylogenetic affiliation and degradation capacity were determined. Three isolates were back inoculated to the manure, resulting in shortened composting process from 5 to 3 days with Germination Index increased up to 134%, and improved compost quality particularly in wheat growth promoting. Comparing to the mesophilic and thermophilic Bacillus, the genomes of the three isolates manifested some features similar to the thermophiles, including smaller genome size and mutation of specific genes that enhance heat tolerance. This study provide robust evidence that microbe-aided thermophilic composting is capable to accelerate manure composting and improve the quality of compost, which represents a new hope to the sustainable use of manure from the meat industry.

Bacillus licheniformisYB06: A Rhizosphere-Genome-Wide Analysis and Plant Growth-Promoting Analysis of a Plant Growth-Promoting Rhizobacterium Isolated from Codonopsis pilosula

Codonopsis pilosula, commonly known as Dangshen, is a valuable medicinal plant, but its slow growth and susceptibility to environmental stress pose challenges for its cultivation. In pursuit of sustainable agricultural practices to enhance the yield and quality of Dangshen, the present study isolated a bacterial strain exhibiting plant growth-promoting potential from the rhizosphere of C. pilosula. This strain was subsequently identified as Bacillus licheniformisYB06. Assessment of its plant growth-promoting attributes revealed the potential of B. licheniformis YB06 as a biofertilizer. Whole-genome sequencing of B. licheniformis YB06 revealed a genome size of 4,226,888 bp with a GC content of 46.22%, harboring 4325 predicted protein-coding sequences. Genomic analysis of B. licheniformis YB06 revealed a diverse array of genes linked to induced systemic resistance (ISR) and plant growth-promoting (PGP) traits, encompassing phytohormone production, nitrogen assimilation and reduction, siderophore biosynthesis, phosphate solubilization, biofilm formation, synthesis of PGP-related amino acids, and flagellar motility. Seed germination assays demonstrated the positive effects of B. licheniformis YB06 on the germination and growth of C. pilosula seedlings. Furthermore, we explored various fertilization regimes, particularly the B. licheniformis YB06-based biofertilizer, were investigated for their impact on the structure and diversity of the C. pilosula rhizosphere soil bacterial community. Our findings revealed that fertilization significantly impacted soil bacterial composition and diversity, with the combined application of B. licheniformis YB06-based biofertilizer and organic fertilizer exhibiting a particularly pronounced enhancement of rhizosphere bacterial community structure and diversity. This study represents the first report on the beneficial effects of B. licheniformis YB06 on both the growth of C. pilosula and the composition of its rhizosphere soil microbial community. These findings provide a theoretical foundation and practical guidance for the development of novel bio-organic compound fertilizers, thereby contributing to the sustainable cultivation of C. pilosula.

Auxin-Producing Bacteria Used as Microbial Biostimulants Improve the Growth of Tomato (Solanum lycopersicum L.) Seedlings in Hydroponic Systems

Seven auxin-producing endophytic bacterial strains (Azospirillum spp., Methylobacterium symbioticum, Bacillus spp.), and two different combinations of these strains were used to verify their influence on tomato during germination and development in hydroponic conditions where, as a novelty for Canestrino di Lucca cultivar, endophytic bacteria were inoculated. To emphasize the presence of bacterial auxins in roots and stems of seedlings, both in situ staining qualitative assessment and quantitative analysis were carried out. Moreover, hypogeal and epigeal growth of the plantlets were measured, and correlation analyses were conducted to examine the relationship between the amount of indolacetic acid (IAA) produced by the bacterial strains and root and stem parameters. Plantlets treated with microbial inoculants showed a significant increase in the survival rate compared to the control treatment. The best results as IAA producers were from Azospirillum baldaniorum Sp245 and A. brasilense Cd, which also induced significant root growth. On the other hand, Bacillus amyloliquefaciens and B. licheniformis induced the best rates in stem growth. These findings highlight the potential for using endophytic bacterial strains in a hydroponic co-cultivation system that enables inoculating plantlets, at an early stage of growth (5 days old).

Advancing Bacillus licheniformis as a Superior Expression Platform through Promoter Engineering

Bacillus licheniformis is recognised as an exceptional expression platform in biomanufacturing due to its ability to produce high-value products. Consequently, metabolic engineering of B. licheniformis is increasingly pursued to enhance its utility as a biomanufacturing vehicle. Effective B. licheniformis cell factories require promoters that enable regulated expression of target genes. This review discusses recent advancements in the characterisation, synthesis, and engineering of B. licheniformis promoters. We highlight the application of constitutive promoters, quorum sensing promoters, and inducible promoters in protein and chemical synthesis. Additionally, we summarise efforts to expand the promoter toolbox through hybrid promoter engineering, transcription factor-based inducible promoter engineering, and ribosome binding site (RBS) engineering.

Bacillus-derived consortium enhances Ginkgo biloba's health and resistance to Alternaria tenuissima

BACKGROUND

Bacillus, as a plant-growth-promoting rhizobacteria, can enhance the resistance of plants to phytopathogens. In our study, Bacillus strains showing excellent biocontrol were screened and used to control ginkgo leaf blight (Alternaria tenuissima).

RESULTS

Four biocontrol Bacillus strains-Bsa537, Bam337, Bso544, and Bsu503-were selected from 286 isolates based on their capacity to inhibit pathogens and promote plant growth. The four Bacillus strains significantly improved the resistance of ginkgo to leaf blight. This was especially the case when the four strains were used as a mixture, which contributed to a decrease in lesion area of >40%. Hence, a mixture of Bacillus strains was used to control ginkgo leaf blight in the field. Treatment efficiency varied from 30% to 100% (average 81.5%) and was higher than that of the control (-2% to -18%, average - 8.5%); the antioxidant capacity of the treated ginkgo was also stronger. In addition, ginkgo biomass increased as a result of treatment with the Bacillus mixture, including leaf weight, area, thickness, number of lateral roots and root weight. Furthermore, the Bacillus mixture improved the ginkgo rhizosphere soil by boosting the number of beneficial microorganisms, lowering the number of pathogens and hastening soil catabolism.

CONCLUSION

The Bacillus mixture improved the health status of ginkgo by protecting it from pathogen attack, promoting its growth and improving the microorganism community in the rhizosphere. This work closes a technological gap in the biological control of ginkgo leaf blight, investigates application methods for compound Bacillus biofertilizers and establishes a framework for the popularity and commercialization of these products. © 2024 Society of Chemical Industry.

Assessment of Plant Growth Promotion Potential of Endophytic Bacterium B. subtilis KU21 Isolated from Rosmarinus officinalis

The current study aimed to evaluate the plant growth-promoting (PGP) potential of endophytic strain Bacillus subtilis KU21 isolated from the roots of Rosmarinus officinalis. The strain exhibited multiple traits of plant growth promotion viz., phosphate (P) solubilization, nitrogen fixation, indole-3-acetic acid (IAA), siderophore, hydrogen cyanide (HCN), lytic enzymes production, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. The isolate also exhibited antagonistic activity against phytopathogenic fungi, i.e., Fusarium oxysporum, Fusarium graminiarum, and Rhizoctonia solani. The P-solubilization activity of B. subtilis KU21 was further elucidated via detection of glucose dehydrogenase (gdh) gene involved in the production of gluconic acid which is responsible for P-solubilization. Further, B. subtilis KU21 was evaluated for in vivo growth promotion studies of tomato (test crop) under net house conditions. A remarkable increase in seed germination, plant growth parameters, nutrient acquisition, and soil quality parameters (NPK) was observed in B. subtilis KU21-treated plants over untreated control. Hence, the proposed module could be recommended for sustainable tomato production in the Northwest Himalayan region without compromising soil health and fertility.

Isolation and identification of a new Bacillus glycinifermentans strain from date palm rhizosphere and its effect on barley seeds under heavy metal stress

Soil contamination by heavy metals is one of the major problems that adversely decrease plant growth and biomass production. Inoculation with the plant growth-promoting rhizobacteria (PGPR) can attenuate the toxicity of heavy metals and enhancing the plant growth. In this study, we evaluated the potential of a novel extremotolerant strain (IS-2 T) isolated from date palm rhizosphere to improve barley seedling growth under heavy metal stress. The species-level identification was carried out using morphological and biochemical methods combined with whole genome sequencing. The bacterial strain was then used in vitro for inoculating Hordeum vulgare L. exposed to three different Cr, Zn, and Ni concentrations (0.5, 1, and 2 mM) in petri dishes and different morphological parameters were assessed. The strain was identified as Bacillus glycinifermentans species. This strain showed high tolerance to pH (6-11), salt stress (0.2-2 M), and heavy metals. Indeed, the minimum inhibitory concentrations at which bacterium was unable to grow were 4 mM for nickel, 3 mM for zinc, more than 8 mM for copper, and 40 mM for chromium, respectively. It was observed that inoculation of Hordeum vulgare L. under metal stress conditions with Bacillus glycinifermentans IS-2 T stain improved considerably the growth parameters. The capacity of the IS-2 T strain to withstand a range of abiotic stresses and improve barley seedling development under lab conditions makes it a promising candidate for use as a PGPR in zinc, nickel, copper, and chromium bioremediation.