Bacillus for Plant Growth Promotion and Stress Resilience: What Have We Learned?

Abstract

The rhizosphere is a thin film of soil that surrounds plant roots and the primary location of nutrient uptake, and is where important physiological, chemical, and biological activities are occurring. Many microbes invade the rhizosphere and have the capacity to promote plant growth and health. Bacillus spp. is the most prominent plant growth promoting rhizobacteria due to its ability to form long-lived, stress-tolerant spores. Bacillus-plant interactions are driven by chemical languages constructed by a wide spectrum of metabolites and lead to enhanced plant growth and defenses. Thus, this review is a synthesis and a critical assessment of the current literature on the application of Bacillus spp. in agriculture, highlighting gaps that remain to be explored to improve and expand on the Bacillus-based biostimulants. Furthermore, we suggest that omics sciences, with a focus on metabolomics, offer unique opportunities to illuminate the chemical intercommunications between Bacillus and plants, to elucidate biochemical and molecular details on modes of action of Bacillus-based formulations, to generate more actionable insights on cellular and molecular events that explain the Bacillus-induced growth promotion and stress resilience in plants.

Bacilli Rhizobacteria as Biostimulants of Growth and Production of Sesame Cultivars under Water Deficit

“…In an experiment with peanut genotypes treated with bacterial strains and under water deficit, minimal differences were observed in relation to water restriction [ 41 ]. Despite the plants showing reductions in root growth, the bacterial strains were efficient in promoting growth and water deficit attenuation, emphasizing the importance of using inoculants to mitigate the effects of water deficit [ 12 , 41 ].…”

“…Based on these results, it is possible to identify a significant contribution of inoculants to the plant growth attributes of the investigated sesame cultivars, implying a beneficial action and a biosustainable alternative for the crop, with a view to reducing and/or replacing chemical fertilizers. The use of biofertilizers before, during, and after environmental stress can promote adjustments in plant defense mechanisms and increase soil water retention capacity, growth, and root performance [ 2 , 12 , 23 , 24 , 42 ].…”

“…These bacteria could be used as inoculants in agriculture since biofertilizers with high concentrations of microorganisms act on the growth and development of plants, increasing crop production, preserving soil life, reducing production costs, without causing damage to water resources or emissions of pollutants, and acting upon soil bioremediation [ 9 , 10 ]. In addition, due to the mitigating action on the negative effects caused by biotic and abiotic stresses [ 11 , 12 ], inoculants can be used as a strategy to promote various agricultural crops in arid and semi-arid environments. In drylands, the effects of inoculants are already observed in several crops, for example, maize ( Zea mays ) [ 13 ], sorghum ( Sorghum bicolor ) [ 14 ], pear-millet ( Pennissetum glaucum ) [ 15 ], and sesame ( Sesamum indicum ) [ 16 , 17 ], indicating the potential of selected bacteria for agricultural applications in the field.…”

Geographically Disperse, Culturable Seed-Associated Microbiota in Forage Plants of Alfalfa (Medicago sativa L.) and Pitch Clover (Bituminaria bituminosa L.): Characterization of Beneficial Inherited Strains as Plant Stress-Tolerance Enhancers

“…The multiple samples showed a series of highly relevant beneficial populations, with the rest of the isolated strains previously described as promoters of plant growth. Thus, the strains Bacillus cereus , Bacillus nealsonii , Priestia megaterium , Pantoea agglomerans , Enterobacter ludwigii , Stenotrophomonas maltophilia , Paenibacillus pabuli , Paenibacillus peoriae and Paenibacillus polymyxa are highly recognized as growth promoters in different plant species [ 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 ]. Others, such as Enterobacter hormaechei , Atlantibacter hermannii , Paenibacillus amylolyticus , Paenibacillus tundrae and Paenibacillus xylanexedens , have less support in the literature, but have also been reported as beneficial or characterized as potentially beneficial due to their abilities, such as phytohormone production or the solubilization/mobilization of inaccessible nutrients [ 89 , 90 , 91 , 92 , 93 , 94 ].…”

Fungi That Promote Plant Growth in the Rhizosphere Boost Crop Growth

“…The second process affecting the rhizobiome takes place through the sensing and response to plants or microbe compounds of low molecular weight [ 135 ], leading to a cellular reaction(s) that is curtailed by the substance being perceived through the following processes: catabolism, transformation, resistance, etc. This constitutes a restrictive cascade that eventually results in the transcription of loci in reaction to a specific compound.…”