Metabolomic insight into the synergistic mechanism of action of a bacterial consortium in plant growth promotion

Microbial crosstalk: decoding interactions to generate efficient SynComs

Limited studies have explored the complex and intense crosstalk between microbes within synthetic microbial communities (SynComs). Here, we highlight recent findings by Zohair et al., who unraveled the metabolic interactions between co-cultured microbes. We provide insights and perspectives for harnessing these interactions to design efficient SynComs for sustainable agriculture.

Screening halotolerant bacteria for their potential as plant growth-promoting and coal-solubilizing agents

The bioconversion of salinized land into healthy agricultural systems by utilizing low-rank coal (LRC) is a strategic approach for sustainable agricultural development. The aims of this study were: (1) to isolate bacterial strains associated with the rhizosphere of native plants in coal-containing soils, (2) to characterize their plant growth-promoting (PGP) and coal-solubilizing capabilities under laboratory conditions and (3) to evaluate their influence on the germination and growth of chia seeds under saline stress. Fourteen bacterial cultures were isolated from the rhizosphere of Artemisia annua L. using culture media containing salt and coal. Based on their PGP activities (nitrogen fixation, phosphate solubilization, siderophore and indole-3-acetic acid production), five strains were selected, belonging to the genera Bacillus, Phyllobacterium, Arthrobacter, and Pseudomonas. Solubilization assays were conducted to confirm the ability of these strains to utilize coal efficiently. Finally, the selected strains were inoculated with chia seeds (Salvia hispanica L.) to evaluate their ameliorating effect under saline stress conditions in coal-containing media. Inoculation with A. subterraneus Y1 resulted in the highest germination and growth metrics of chia seeds. A positive but comparatively weaker response was observed with P. frederiksbergensis AMA1 and B. paramycoides Lb-1 as inoculants. Coal inoculated with halotolerant bacteria can serve as the foundation for humified organic matter in salt-affected environments. The selected halotolerant bacteria enhance coal biotransformation while exhibiting PGP traits.

Development of bacterial bioformulations using response surface methodology

AIM

Bacterial consortia exhibiting plant growth promoting properties have emerged as a sustainable approach for crop improvement. As the main challenge associated with them is loss of viability and performance under natural conditions, a robust approach for designing bioformulation is needed. In this study, an efficient bioformulation was developed using spontaneous mutants of three bacterial strains for growth promotion of Cajanus cajan.

METHODS AND RESULTS

Optimization of additives for solid [carboxymethylcellulose (CMC), and glycerol] and liquid [polysorbate, CMC, and polyvinyl pyrrolidone (PVP)] bioformulations was done by response surface methodology using central composite design. The stability of each bioinoculant in the formulation was assessed at 30°C and 4°C. The efficiency of the liquid bioformulation was checked in planta in sterile, and subsequently in non-sterile, soil. The maximum cell count was observed in solid bioformulation with 0.1 g l-1 CMC and 50% glycerol (8.10 × 108, 3.69 × 108, and 7.39 × 108 CFU g-1 for Priestia megaterium, Azotobacter chroococcum, and Pseudomonas sp. SK3, respectively) and in liquid bioformulation comprising 1% PVP, 0.1 g l-1 CMC, and 0.025% polysorbate (8 × 109, 3.8 × 109, and 6.82 × 109 CFU ml-1 for P. megaterium, A. chroococcum, and Pseudomonas sp. SK3, respectively). The bioinoculants showed a higher viability (6 months) at 4°C compared to 30°C. Triple culture consortium enhanced plant growth in comparison to the control. The strains could be detected in soil till 45 days after sowing.

CONCLUSIONS

The study established a systematic process for developing a potent bioformulation to promote agricultural sustainability. Using mutant strains, the bioinoculants could be tracked. In planta assays revealed that the triple culture consortium out-performed mono and dual cultures in terms of impact on plant growth.

Bacterial exopolysaccharide amendment improves the shelf life and functional efficacy of bioinoculant under salinity stress

AIM

Bacterial exopolysaccharides (EPS) possess numerous properties beneficial for the growth of microbes and plants under hostile conditions. The study aimed to develop a bioformulation with bacterial EPS to enhance the bioinoculant's shelf life and functional efficacy under salinity stress.

METHODS AND RESULTS

High EPS-producing and salt-tolerant bacterial strain (Bacillus haynessi SD2) exhibiting auxin-production, phosphate-solubilization, and biofilm-forming ability, was selected. EPS-based bioformulation of SD2 improved the growth of three legumes under salt stress, from which pigeonpea was selected for further experiments. SD2 improved the growth and lowered the accumulation of stress markers in plants under salt stress. Bioformulations with varying EPS concentrations (1% and 2%) were stored for 6 months at 4°C, 30°C, and 37°C to assess their shelf life and functional efficacy. The shelf life and efficacy of EPS-based bioformulation were sustained even after 6 months of storage at high temperature, enhancing pigeonpea growth under stress in both control and natural conditions. However, the efficacy of non EPS-based bioformulation declined following four months of storage. The bioformulation (with 1% EPS) modulated bacterial abundance in the plant's rhizosphere under stress conditions.

CONCLUSION

The study brings forth a new strategy for developing next-generation bioformulations with higher shelf life and efficacy for salinity stress management in pigeonpea.

Microbial Consortia: Promising Tool as Plant Bioinoculants for Agricultural Sustainability

In the present scenario, growing population demands more food, resulting in the need for sustainable agriculture. Numerous approaches are explored in response to dangers and obstacles to sustainable agriculture. A viable approach is to be exploiting microbial consortium, which generate diverse biostimulants with growth-promoting characteristics for plants. These bioinoculants play an indispensable role in optimizing nutrient uptake efficiency mitigating environmental stress. Plant productivity is mostly determined by the microbial associations that exist at the rhizospheric region of plants. The engineered consortium with multifunctional attributes can be effectively employed to improve crop growth efficacy. A number of approaches have been employed to identify the efficient consortia for plant growth and enhanced crop productivity. Various plant growth-promoting (PGP) microbes with host growth-supporting characteristics were investigated to see if they might work cohesively and provide a cumulative effect for improved growth and crop yield. The effective microbial consortia should be assessed using compatibility tests, pot experimentation techniques, generation time, a novel and quick plant bioassay, and sensitivity to external stimuli (temperature, pH). The mixture of two or more microbial strains found in the root microbiome stimulates plant growth and development. The present review deals with mechanism, formulation, inoculation process, commercialization, and applications of microbial consortia as plant bioinoculants for agricultural sustainability.

Seed biopriming as a promising approach for stress tolerance and enhancement of crop productivity: a review

Chemicals are used extensively in agriculture to increase crop production to meet the nutritional needs of an expanding world population. However, their injudicious application adversely affects the soil's physical, chemical and biological properties, subsequently posing a substantial threat to human health and global food security. Beneficial microorganisms improve plant health and productivity with minimal impact on the environment; however, their efficacy greatly relies on the application technique. Biopriming is an advantageous technique that involves the treatment of seeds with beneficial biological agents. It exhibits immense potential in improving the physiological functioning of seeds, thereby playing a pivotal role in their uniform germination and vigor. Biopriming-mediated molecular and metabolic reprogramming imparts stress tolerance to plants, improves plant health, and enhances crop productivity. Furthermore, it is also associated with rehabilitating degraded land, and improving soil fertility, health and nutrient cycling. Although biopriming has vast applications in the agricultural system, its commercialization and utilization by farmers is still in its infancy. This review aims to critically analyze the recent studies based on biopriming-mediated stress mitigation by alteration in physiological, metabolic and molecular processes in plants. Additionally, considering the necessity of popularizing this technique, the major challenges and prospects linked to the commercialization and utilization of this technique in agricultural systems have also been discussed. © 2023 Society of Chemical Industry.

Contribution of Biofertilizers to Pulse Crops: From Single-Strain Inoculants to New Technologies Based on Microbiomes Strategies

Pulses provide distinct health benefits due to their low fat content and high protein and fiber contents. Their grain production reaches approximately 93,210 × 103 tons per year. Pulses benefit from the symbiosis with atmospheric N2-fixing bacteria, which increases productivity and reduces the need for N fertilizers, thus contributing to mitigation of environmental impact mitigation. Additionally, the root region harbors a rich microbial community with multiple traits related to plant growth promotion, such as nutrient increase and tolerance enhancement to abiotic or biotic stresses. We reviewed the eight most common pulses accounting for almost 90% of world production: common beans, chickpeas, peas, cowpeas, mung beans, lentils, broad beans, and pigeon peas. We focused on updated information considering both single-rhizobial inoculation and co-inoculation with plant growth-promoting rhizobacteria. We found approximately 80 microbial taxa with PGPR traits, mainly Bacillus sp., B. subtilis, Pseudomonas sp., P. fluorescens, and arbuscular mycorrhizal fungi, and that contributed to improve plant growth and yield under different conditions. In addition, new data on root, nodule, rhizosphere, and seed microbiomes point to strategies that can be used to design new generations of biofertilizers, highlighting the importance of microorganisms for productive pulse systems.