Molecular characterization of a novel strain of Bacillus halotolerans protecting wheat from sheath blight disease caused by Rhizoctonia solani Kühn

Survival strategies of Bacillus spp. in saline soils: Key factors to promote plant growth and health

Soil salinity is one of the most important abiotic factors that affects agricultural production worldwide. Because of saline stress, plants face physiological changes that have negative impacts on the various stages of their development, so the employment of plant growth-promoting bacteria (PGPB) is one effective means to reduce such toxic effects. Bacteria of the Bacillus genus are excellent PGPB and have been extensively studied, but what traits makes them so extraordinary to adapt and survive under harsh situations? In this work we review the Bacillus' innate abilities to survive in saline stressful soils, such as the production osmoprotectant compounds, antioxidant enzymes, exopolysaccharides, and the modification of their membrane lipids. Other survival abilities are also discussed, such as sporulation or a reduced growth state under the scope of a functional interaction in the rhizosphere. Thus, the most recent evidence shows that these saline adaptive activities are important in plant-associated bacteria to potentially protect, direct and indirect plant growth-stimulating activities. Additionally, recent advances on the mechanisms used by Bacillus spp. to improve the growth of plants under saline stress are addressed, including genomic and transcriptomic explorations. Finally, characterization and selection of Bacillus strains with efficient survival strategies are key factors in ameliorating saline problems in agricultural production.

Genomic insight into the salt tolerance and proteolytic activity of Bacillus subtilis

We assessed the salt tolerance and proteolytic activity of 40 genome-published Bacillus subtilis strains isolated from fermented Korean foods to illuminate the genomic background behind the functionality of B. subtilis in high-salt fermentation. On the basis of the salt tolerance and phenotypic proteolytic activity of the 40 strains, we selected five strains exhibiting different phenotypic characteristics. Comparative genomic analyses of these five strains provided genomic insight into the salt tolerance and proteolytic activity of B. subtilis. Two-component system (TCS) genes annotated as ybdGJK and laterally acquired authentic ATP-binding cassette (ABC) transporter system genes of tandem repeat structure might contribute to increase salt tolerance. The additional possession of gene homologs for CAAX protease family proteins and components of Clp (caseinolytic protease) complex, ATP-dependent Clp proteolytic subunit ClpP and AAA+ (ATPases associated with diverse cellular Activities) family ATPases, might determine the proteolytic activity of B. subtilis. This study established the scientific foundation for the viability and functionality of B. subtilis in high-salt fermentation.