Deletion of either oxyR or rpoS or both resulted in loss of induction of katG in response to oxidative stress, STA-9090 concentration which suggests that both OxyR and RpoS are required for the induction of katG under these conditions. Similarly, dpsA was determined to be regulated by both OxyR and RpoS, although in this case both RpoS and OxyR act independently as positive transcriptional regulators of dpsA expression. The effect of deletion of rpoS on dpsA expression under normal growth conditions was markedly greater than deletion of oxyR in a situation analogous to that of katG, where

the repression of katG expression by rpoS was greater than the repression of expression by oxyR. Induction of dpsA expression under conditions of oxidative stress was completely abolished by deletion of rpoS, and largely eliminated by deletion of oxyR, again suggesting that both genes are required for the induction

of dpsA under conditions of oxidative stress. In apparent contradiction of the postulated role of RpoS as a positive regulator of dpsA expression however, semi-quantitative PCR of amounts of dpsA messenger RNA showed an increased degree of dpsA expression in an rpoS mutant during all stages of growth, as compared to a wild type strain. However, previous studies have shown that expression of dpsA under conditions of oxidative stress results from increased transcription from Lenvatinib price the upstream katG promoter (10) and in this study we confirmed that deletion of rpoS results Terminal deoxynucleotidyl transferase in the production of a single 3.5 kb message consisting of katG-dpsA mRNA. Deletion of rpoS results in no specific dpsA transcript, due to the loss of positive regulation by RpoS and a 3.5 kb message produced by transcription from the katG promoter as a result of loss of negative regulation of the katG

promoter by OxyR via RpoS regulation. Overall, the results of this study allow an insight interpretation of the B. pseudomallei RpoS and OxyR regulatory network as summarized in Figure 5. Under normal growth conditions, RpoS positively regulates oxyR and dpsA while negatively regulating the katG-dpsA operon via OxyR. Under conditions of oxidative stress, rpoS expression increases with increasing oxyR expression, and repression of OxyR results in positive regulation of the katG-dpsA. Consequently expression from the katG-dpsA operon is increased independently of dpsA gene expression from its own RpoS promoter, resulting in a global up-regulation of the genes required to cope with the increased oxidative stress. This work was supported by research grants from the National Health Foundation and the Thailand Research Fund. WJ was supported by a Royal Golden Jubilee PhD Scholarship from the Thailand Research Fund and the Commission on Higher Education. The authors wish to thank Prof. Yutaka, Editorial Assistant at the Language Center, Faculty of Science, Mahidol University for critical reading of the manuscript.