Abstract:[Background] Sigma B (SigB) is an RNA polymerase cofactor that determines specific transcription, playing a role in the responses of Bacillus to environmental stress conditions such as high temperatures. Studies have shown that sigB in B. safensis ST7 is upregulated under manganese stress, which indicated that SigB may be involved in the manganese response. However, its molecular regulatory mechanism needs further investigation.[Objective] To reveal the regulatory role of sigB in the response of B. safensis ST7 to manganese stress. [Methods] A sigB-deleted mutant ΔsigB was constructed by homologous recombination (single-switching method) with B. safensis ST7 as the starting strain. Changes in tolerance to manganese, motility, biofilm formation, and sporulation rate of the mutant were analyzed, and the transcript levels of the biofilm- and spore-associated gene spo0A and the flagellum-associated gene flgD in ΔsigB were determined by RT-qPCR. [Results] The sequencing results demonstrated that the last part of sigB was replaced by a kanamycin resistance gene in ΔsigB without sigB expression. Compared with the wild type, ΔsigB showed decreases in the tolerance to manganese, swimming motility, biofilm formation, and sporulation rate. In addition, the deletion of sigB up-regulated the expression of flgD while down-regulating the expression of spo0A.[Conclusion] The results suggest that sigB changes the motility and manganese sensitivity of B. safensis by regulating the expression of genes associated with flagellum, sporulation, and biofilm formation to participate in the response to manganese stress.
