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.

The methylerythritol phosphate pathway is responsible for the biosynthesis of terpenoids, the largest class of secondary metabolites.  Although the structures and functions of the proteins involved in this pathway have been well studied in Bacillus subtilis, only a few studies have reported the transcriptional profile of the genes involved.  Therefore, we analyzed methylerythritol phosphate pathway genes in the genome of B. subtilis 916, which has been developed as a biological control agent against some rice diseases in China.  Our results showed that methylerythritol phosphate pathway genes were distributed throughout the genome of this strain.  These genes were transcribed during both the exponential and stationary phases.  We further confirmed the transcription units of dxs, dxr, ispD, ispF, ipK, ispG, ispH, idi, and ispA in B. subtilis 916 through reverse transcription-PCR analyses; the results showed that these nine genes were located in seven different operons.  The transcript start sites of the seven different operons were determined by 5´-rapid amplification of cDNA ends-PCR.  Thus, our study provides a molecular basis at the transcriptional level for investigating homoterpene synthesis in the methylerythritol phosphate pathway of B. subtilis 916.