Identification of genes involved in regulating MnSOD2 production and root colonization in Bacillus cereus 905

Abstract

sodA2-encoding manganese-containing superoxide dismutase (MnSOD2) in Bacillus cereus 905 plays an essential role in antioxidative stress, nutrition utilization, rhizosphere and phyllosphere colonization. However, the genes involved in regulating the sodA2 expression have not been clearly elucidated in B. cereus. In this study, a genome-wide random insertion mutagenesis was constructed by using transposon TnYLB-1 to identify novel genes regulating the sodA2 expression. Seven mutants that changed the sodA2 expression at both mRNA and protein levels were finally obtained. Sequence analysis and BLAST data showed that the genes disrupted by TnYLB-1 in B. cereus 905 shared high conservations with those in the B. cereus type strain, ATCC 14579. These genes encode heat-inducible transcription repressor, chloride channel protein, recombinase A, ferrous iron transport protein, nucleoside diphosphate kinase, and histidine ammonia-lyase. Besides, we also provided the evidence that the genes regulating the sodA2 expression could influence colonization ability of B. cereus 905 on wheat roots. Specifically, those genes downregulating the sodA2 expression significantly reduced bacterial colonization on wheat roots, and mutants with increased MnSOD2 activities could enhance bacterial population densities on wheat roots to a certain degree. Our work provided information that multiple genes are involved in MnSOD2 production and wheat root colonization. The molecular regulatory pathways through which these genes modulate the sodA2 expression and root colonization need to be investigated extensively in the future.