Abstract

PerR, a member of Fur family protein, is a metal-dependent H2O2 sensing transcription factor that regulates genes in-volved in peroxide stress response. Industrially important bac-terium Bacillus licheniformis contains three PerR-like pro-teins (PerRBL, PerR2, and PerR3) compared to its close rela-tive Bacillus subtilis. Interestingly, unlike other bacteria in-cluding B. subtilis, no authentic perRBL null mutant could be established for B. licheniformis. Thus, we constructed a con-ditional perRBL mutant using a xylose-inducible promoter, and investigated the genes under the control of PerRBL. PerRBL regulon genes include katA, mrgA, ahpC, pfeT, hemA, fur, and perR as observed for PerRBS. However, there is some variation in the expression levels of fur and hemA genes be-tween B. subtilis and B. licheniformis in the derepressed state. Furthermore, katA, mrgA, and ahpC are strongly induced, whereas the others are only weakly or not induced by H2O2 treatment. In contrast to the B. subtilis perR null mutant which frequently gives rise to large colony phenotype mainly due to the loss of katA, the suppressors of B. licheniformis perR mutant, which can form colonies on LB agar, were all cata-lase-positive. Instead, many of the suppressors showed in-creased levels of siderophore production, suggesting that the suppressor mutation is linked to the fur gene. Consistent with this, perR fur double mutant could grow on LB agar without Fe supplementation, whereas perR katA double mutant could only grow on LB agar with Fe supplementation. Taken toge-ther, our data suggest that in B. licheniformis, despite the si-milarity in PerRBL and PerRBS regulon genes, perR is an essen-tial gene required for growth and that the inability of perR null mutant to grow is mainly due to elevated expression of Fur.

• Keywords: Bacillus licheniformis; Fur (ferric uptake regula-tor); hydrogen peroxide; PerR (peroxide sensing repressor