IDENTIFICATION AND CHARACTERIZATION OF GENES THAT PROTECT ESCHERICHIA COLI FROM HYDROGE PEROXIDE MEDIATED OXIDATIVE STRESS

Abstract

<p>Reactive oxygen species are major agents responsible for degenerative disease, ageing, mutagenesis and carcinogenesis. Enteric bacteria, such as Escherichia coli and Salmonella typhimurium, can serve as model cellular systems for understanding the physiological and genetic responses to oxidative stress in higher eukaryotes due to the similarity in the nature of response. The smaller size of the bacterial genome, simpler and well understood bacterial metabolic pathways and relative ease of manipulation of bacteria makes them a preferred tool for certain applications.</p> <p>Enteropathogenic bacteria encounter endogenous toxic oxygen species during aerobic respiration and exogenously during phagocytosis by neutrophils and macrophages. Survival of bacteria under these circumstances depends on a multigene response to oxidative stress. For rapid adaptation, the cell elevates the synthesis of several known antioxidant enzymes such as catalase, superoxide dismutase and also a variety of stress proteins of unknown function. The adaptation and resistance to oxidative stress are thought to be crucial aspects of bacterial pathogenesis.</p> <p>The genes encoding many of the antioxidant response proteins remain unidentified. We have used chromosomal mutagenesis to identify genes that play a protective function during H20 2 generated oxidative stress. The present work reports isolation and characterization of genes that are regulated by OxyR, a member of the LysR family of transcriptional regulators, involved in the regulation of a subset of the oxidative stress induced genes and other OxyR independent genes. One of the genes characterized in this work encodes a putative signal transducer protein (also implicated in iron regulation), known as BarA. Another gene identified in the oxidative stress response is rna, encoding an endoribonucleosidase RNase I.</p> <p>Escherichia coli has two hydroperoxidases that breakdown hydrogen peroxide. The present study shows that the transcription of katG gene, encoding hydroperoxidase I (HPI), regulated by OxyR during peroxidative stress, is also regulated by stationary phase specific sigma factor RpoS during normal growth and during stress generated by weak acids.</p>