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 H2O2. 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 H2O2. 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.

中文翻译：

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recA基因对于介导蜡样芽胞杆菌905在小麦根上的定居至关重要。

蜡状芽胞杆菌905是一种促进植物生长的根际细菌（PGPR），能够在较大种群数量的小麦根部定植。从以前的研究中，我们了解到，编码sodA2的含锰超氧化物歧化酶（MnSOD2）对于蜡状芽孢杆菌905在小麦根际中存活很重要。在这项研究中，我们证明了编码重组酶A的recA基因的缺失在mRNA和蛋白质水平上均显着降低了MnSOD2的表达。通过与野生型比较，ΔrecA暴露于50μM百草枯或15 mM H2O2后细胞存活率显着下降。有证据表明蜡状芽孢杆菌905的recA基因还显着调节营养利用效率，生物膜形成和成群运动。根定殖检查表明，ΔrecA在小麦根上的定殖减少了1000到2500倍，这表明RecA在蜡状芽孢杆菌905对小麦根的有效定居中起着不可或缺的作用。综上所述，recA基因阳性调节MnSOD2的产生和营养利用，并保护蜡状芽胞杆菌905细胞免受百草枯和H2O2的侵害。此外，RecA促进蜡状芽孢杆菌905的生物膜形成和成群运动。最后，RecA极大地促进了蜡状芽孢杆菌905的小麦根定植。我们的结果表明，RecA在蜡状芽孢杆菌905的生理过程中，特别是对于在小麦根上定植，具有重要作用。我们的发现将为研究B的定植机制指出一个研究方向。未来的cereus 905，并提供潜在的有效策略来增强PGPR菌株的生物防治功效。要点：•RecA在蜡状芽孢杆菌的根定殖中起着不可或缺的作用。