Community-forming traits play role in effective colonization of plant-growth-promoting bacteria and improved plant growth.

Community-forming traits (CFts) play an important role in the effective colonization of plant-growth-promoting bacterial communities that influence host plants positively by modulating their adaptive functions. In this study, by considering plant-growth-promoting traits (PGPts) and community-forming traits (CFts), three communities were constructed, viz., SM1 (PGPts), SM2 (CFts), and SM3 (PGPts+CFts). Each category isolates were picked up on the basis of their catabolic diversity of different carbon sources. Results revealed a distinctive pattern in the colonization of the communities possessed with CF traits. It was observed that the community with CFts colonized inside the plant in groups or in large aggregations, whereas the community with only PGPts colonized as separate individual and small colonies inside the plant root and leaf. The effect of SM3 in the microcosm experiment was more significant than the uninoculated control by 22.12%, 27.19%, and 9.11% improvement in germination percentage, chlorophyll content, and plant biomass, respectively. The significant difference shown by the microbial community SM3 clearly demonstrates the integrated effect of CFts and PGPts on effective colonization vis-à-vis positive influence on the host plant. Further detailed characterization of the interaction will take this technology ahead in sustainable agriculture.

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 heatS (heat susceptible, GW322) and heatT (heat tolerant, HD3298 and HD3271) varieties by culturable and unculturable approaches. The results evidenced that the culturable diversity was higher in the heatS variety than in the heatT variety and Bacillus was found to be dominant among the 10 different bacterial genera identified. Though the WSEB population was higher in the heatS variety, a greater number of isolates from the heatT 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 heatT 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.

Characterization of actinobacteria from wheat seeds for plant growth promoting traits and protection against fungal pathogens.

Seeds harbor naturally occurring microbial endophytes that proliferate during seedling development; playing crucial roles in seedling growth, establishment, and protection against fungal pathogens. Resilient actinobacteria of wheat seeds have been explored in this study for their beneficial traits. Ten actinobacteria isolated from the surface-sterilized seeds of wheat variety HD3117 were identified as nine species of Streptomyces and one of Nocardiopsis. Most isolates could grow at 42°C, 5% NaCl, and 10% poly ethylene glycol (PEG); exhibited variable hydrolytic enzyme production for amylase, cellulase, and protease. Few isolates produced indole acetic acid (9.0-18.9 µg ml-1 ) and could solubilize P (11.3-85.2 µg ml-1 ). The isolates were antagonistic against one or more fungal pathogens under test (Fusarium graminearum, Bipolaris sorokiniana, Alternaria sp., and Tilletia indica), of which Streptomyces sampsonii WSA20 inhibited all in dual culture assay. Priming of wheat seeds with the efficient isolate WSA20 led to effective colonization in the root zone and significantly improved germination, shoot and root length in seed germination assay. Significant protection was recorded in microcosm experiment where no symptoms of disease were observed. This study shows the significance of actinobacterial endophytes of wheat seeds in influencing seed germination and seedling growth while protecting from soil-borne pathogens. It is original and suggests that the seed inhabiting efficient actinobacteria may be developed as efficient bioinoculant for sustainable farming system.

Prospecting catabolic diversity of microbial strains for developing microbial consortia and their synergistic effect on Lentil (Lens esculenta) growth, yield and iron biofortification.

Carbon profiling of heterotrophic microbial inoculants is worthwhile strategy for formulating consortium-based biofertilizers. Consortium-based biofertilizers are better than single strain-based biofertilizers for sustaining agricultural productivity and enhancing micronutrient concentration in grains. Currently, we investigated catabolic diversity among microbes using different carbon sources and certain enzyme activities. A field experiment was also carried to evaluate the synergistic effect of selected lentil Rhizobia and plant growth promoting rhizobacteria strains on lentil growth, yield, nitrogen fixation, and Fe-content in seeds. On the basis of carbon profiling Bacillus sp. RB1 and Pseudomonas sp. RP1 were selected for synergistic study with lentil Rhizobium-Rhizobium leguminosarum subsp. viciae RR1. Co-inoculation of Rhizobium with Bacillus sp. RB1 and Pseudomonas sp. RP1 significantly enhanced the plant height, number of pods per plant, seed yield, number of nodules per plant, nitrogenase activity and Fe biofortification in seed over the single Rhizobium inoculation or dual combination of Rhizobium + RB1 or RP1.The response of single Rhizobium inoculation or co-inoculation of Rhizobium with RB1 and/or RP1 at 50% RDF was almost similar or higher than full dose of recommended N:P:K with respect to lentil yield and Fe biofortification in seed. This deciphered grouping of microbial strains for formulation of microbial consortia-based biofertilizers and revealed the promise of consortium of Rhizobium and plant growth promoting rhizobacteria in improving the biological yield and enhancing the Fe content of lentil seed.

Microbial Community and Function-Based Synthetic Bioinoculants: A Perspective for Sustainable Agriculture.

Interactions among the plant microbiome and its host are dynamic, both spatially and temporally, leading to beneficial or pathogenic relationships in the rhizosphere, phyllosphere, and endosphere. These interactions range from cellular to molecular and genomic levels, exemplified by many complementing and coevolutionary relationships. The host plants acquire many metabolic and developmental traits such as alteration in their exudation pattern, acquisition of systemic tolerance, and coordination of signaling metabolites to interact with the microbial partners including bacteria, fungi, archaea, protists, and viruses. The microbiome responds by gaining or losing its traits to various molecular signals from the host plants and the environment. Such adaptive traits in the host and microbial partners make way for their coexistence, living together on, around, or inside the plants. The beneficial plant microbiome interactions have been exploited using traditional culturable approaches by isolating microbes with target functions, clearly contributing toward the host plants' growth, fitness, and stress resilience. The new knowledge gained on the unculturable members of the plant microbiome using metagenome research has clearly indicated the predominance of particular phyla/genera with presumptive functions. Practically, the culturable approach gives beneficial microbes in hand for direct use, whereas the unculturable approach gives the perfect theoretical information about the taxonomy and metabolic potential of well-colonized major microbial groups associated with the plants. To capitalize on such beneficial, endemic, and functionally diverse microbiome, the strategic approach of concomitant use of culture-dependent and culture-independent techniques would help in designing novel "biologicals" for various crops. The designed biologicals (or bioinoculants) should ensure the community's persistence due to their genomic and functional abilities. Here, we discuss the current paradigm on plant-microbiome-induced adaptive functions for the host and the strategies for synthesizing novel bioinoculants based on functions or phylum predominance of microbial communities using culturable and unculturable approaches. The effective crop-specific inclusive microbial community bioinoculants may lead to reduction in the cost of cultivation and improvement in soil and plant health for sustainable agriculture.