Social behaviors shift properties that are beneficial to plants in two-member consortia of Bacillus velezensis

Bacillus spp. strains that are beneficial to plants are widely used in commercial biofertilizers and biocontrol agents for sustainable agriculture. Generally, functional Bacillus strains are applied as single strain communities since the principles of synthetic microbial consortia constructed with Bacillus strains remain largely unclear. Here, we demonstrated that the kin discrimination system directly affects the survival and function of two-member consortia composed of B. velezensis SQR9 and FZB42 in the rhizosphere. A mutation in the global regulator Spo0A of SQR9 markedly reduced the boundary phenotype with wild-type FZB42, and the combined use of the spo0A mutant and FZB42 improved biofilm formation, root colonization and the production of secondary metabolites that are beneficial to plants. We further confirmed the correlation between the swarm discrimination phenotype within community members and effects that are beneficial to plants in greenhouse experiments. Our results provide evidence that social interactions among bacteria could be an influencing factor in achieving a desired community-level function.