Abstract
BackgroundBurkholderia pseudomallei, the causative agent of melioidosis, is a Gram-negative bacterium widely distributed in soil and water in endemic areas. This soil saprophyte can survive harsh environmental conditions, even in soils where herbicides (containing superoxide generators) are abundant. Sigma factor E (σE) is a key regulator of extra-cytoplasmic stress response in Gram-negative bacteria. In this study, we identified the B. pseudomallei σE regulon and characterized the indirect role that σE plays in the regulation of spermidine, contributing to the successful survival of B. pseudomallei in stressful environments.ResultsChanges in the global transcriptional profiles of B. pseudomallei wild type and σE mutant under physiological and oxidative stress (hydrogen peroxide) conditions were determined. We identified 307 up-regulated genes under oxidative stress condition. Comparison of the transcriptional profiles of B. pseudomallei wild type and σE mutant under control or oxidative stress conditions identified 85 oxidative-responsive genes regulated by σE, including genes involved in cell membrane repair, maintenance of protein folding and oxidative stress response and potential virulence factors such as a type VI secretion system (T6SS). Importantly, we identified that the speG gene, encoding spermidine-acetyltransferase, is a novel member of the B. pseudomallei σE regulon. The expression of speG was regulated by σE, implying that σE plays an indirect role in the regulation of physiological level of spermidine to protect the bacteria during oxidative stress.ConclusionThis study identified B. pseudomallei genes directly regulated by σE in response to oxidative stress and revealed the indirect role of σE in the regulation of the polyamine spermidine (via regulation of speG) for bacterial cell protection during oxidative stress. This study provides new insights into the regulatory mechanisms by which σE contributes to the survival of B. pseudomallei under stressful conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-787) contains supplementary material, which is available to authorized users.
Highlights
Burkholderia pseudomallei, the causative agent of melioidosis, is a Gram-negative bacterium widely distributed in soil and water in endemic areas
Analyses of the profiles revealed a total of 649 genes (Additional file 1) that were differentially regulated (≥1 absolute log-transformed fold change) representing approximately 11.0% of all B. pseudomallei K96243 genes
Since the objective of this study was to identify B. pseudomallei gene expression in response to oxidative stress, we focused on the analysis of the up-regulated genes
Summary
Burkholderia pseudomallei, the causative agent of melioidosis, is a Gram-negative bacterium widely distributed in soil and water in endemic areas. This soil saprophyte can survive harsh environmental conditions, even in soils where herbicides (containing superoxide generators) are abundant. B. pseudomallei is intrinsically resistant to several antibiotics and treatment typically involves an initial parenteral phase of therapy, B. pseudomallei must be able to activate the appropriate genes and regulate their expression. Many of these genes are organized into regulons which are under the control of sigma factors. Typhimurium σE mutant identified the σE regulon and virulence factors that contributed to disease [11,12]
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