The recA gene is crucial to mediate colonization of Bacillus cereus 905 on wheat roots.

Bacillus cereus 905, one of the plant growth-promoting rhizobacteria (PGPRs), is capable of colonizing wheat roots in a large population size. From previous studies, we learned that the sodA2-encoding manganese-containing superoxide dismutase (MnSOD2) is important for B. cereus 905 to survive in wheat rhizosphere. In this investigation, we demonstrated that deletion of the recA gene, which codes for the recombinase A, significantly reduced MnSOD2 expression at both the mRNA and the protein levels. Through comparison with the wild-type, the ∆recA showed a dramatic decrease in cell survival after exposure to 50 μM paraquat or 15 mM HO. Evidence indicated that the recA gene of B. cereus 905 also notably regulated nutrition utilization efficiency, biofilm formation, and swarming motility. The root colonization examination showed that the ∆recA had a 1000- to 2500-fold reduction in colonization on wheat roots, suggesting that RecA plays an indispensable role in effective colonization on wheat roots by B. cereus 905. Taken together, the recA gene positively regulates MnSOD2 production and nutrition utilization and protects B. cereus 905 cells against paraquat and HO. Besides, biofilm formation and swarming motility of B. cereus 905 are promoted by RecA. Finally, RecA significantly contributes to wheat root colonization of B. cereus 905. Our results showed the important role of RecA during physiological processes in B. cereus 905, especially for colonization on wheat roots. Our findings will point out a research direction to study the colonization mechanisms of B. cereus 905 in the future and provide potential effective strategy to enhance the biocontrol efficacy of PGPR strains. KEY POINTS : • RecA plays an indispensable role in root colonization of B. cereus.