IDENTIFICATION OF BACILLUS ANTHRACIS FACTORS INVOLVED IN OXIDATIVE STRESS RESPONSE BY COMPARATIVE TRANSCRIPTOME ANALYSIS OF WILD-TYPE AND ΔHTRA STRAINS

Disruption of the unique Bacillus anthracis htrA locus (encoding for the extracellular chaperone/protease HtrA) results in increased susceptibility to peroxide treatment in vitro, which may account for the observed delayed expansion of the mutated strains in macrophages. We have recently conducted a comparative transcriptomic study which revealed differential gene expression in response to peroxide treatment in wild type vs. ΔhtrA mutant. The genes exhibiting H₂O₂-modulated expression could be divided into three categories; genes similarly modulated in both wild-type and mutant, and genes uniquely modulated either in the wild-type or the mutant strain. We identified 15 genes which are uniquely up-regulated (>6 fold) in the wild-type strain and determined which of these are specifically required for the ability of B. anthracis to withstand oxidative stress, and are not modulated by other stress regimens such as heat and osmotic stress. By RT real-time PCR, we identified four genes (GBAA2058, GBAA3227/8, GBAA3800 and GBAA4735/6) that are up-regulated uniquely in the wild-type strain, and only upon peroxide exposure. MazG, the product of the GBAA3800 locus, is a highly conserved nucleoside triphosphate pyrophosphohydrolase, which plays a role in cellular "house cleaning" by removing abnormal dNTPs. MazG has been shown to be involved in various stress conditions in different bacteria. CheY, the product of the GBAA4736 locus, is a major chemotaxis-related response regulator in Bacillus and other bacteria, which has been shown to be indirectly modified by HtrA in Borrelia burgdorferi. Studies which address the role of these genes in the response of B. anthracis to oxidative stress are currently performed.