Role of the ArcAB two-component system in the resistance of Escherichia coli to reactive oxygen stress

<p>Abstract</p> <p>Background</p> <p>The global regulatory system ArcAB controls the anaerobic growth of <it>E. coli</it>, however, its role in aerobic conditions is not well characterized. We have previously reported that ArcA was necessary for <it>Salmonella </it>to resist reactive oxygen species (ROS) in aerobic conditions.</p> <p>Results</p> <p>To investigate the mechanism of ROS resistance mediated by ArcAB, we generated deletion mutants of ArcA and ArcB in <it>E. coli</it>. Our results demonstrated that both ArcA and ArcB were necessary for resistance to hydrogen peroxide (H₂O₂), a type of ROS, and their function in this resistance was independent from H₂O₂scavenge. Mutagenesis analysis of ArcA indicated that ROS resistance was mediated through a distinct signaling pathway from that used in anaerobic conditions. An abundant protein flagellin was elevated at both the protein and mRNA levels in the <it>ΔarcA </it>mutant as compared to the wild type <it>E. coli</it>, and deletion of flagellin restored the resistance of the <it>ΔarcA </it>mutant to H₂O₂. The resistance of the <it>ΔarcA </it>mutant <it>E. coli </it>to H₂O₂can also be restored by amino acid supplementation, suggesting that a deficiency in amino acid and/or protein synthesis in the mutant contributed to its susceptibility to H₂O₂, which is consistent with the notion that protein synthesis is necessary for ROS resistance.</p> <p>Conclusion</p> <p>Our results suggest that in addition to its role as a global regulator for anaerobic growth of bacteria, ArcAB system is also important for bacterial resistance to ROS in aerobic conditions, possibly through its influence on bacterial metabolism, especially amino acid and/or protein assimilation and synthesis.</p

Identification of Genes Associated with Survival of Salmonella enterica Serovar Enteritidis in Chicken Egg Albumen

Salmonella enterica consists of over 2,000 serovars that are major causes of morbidity and mortality associated with contaminated food. Despite similarities among serovars of Salmonella enterica, many demonstrate unique host specificities, epidemiological characteristics, and clinical manifestations. One of the unique epidemiological characteristics of the serovar Enteritidis is that it is the only bacterium routinely transmitted to humans through intact chicken eggs. Therefore, Salmonella enterica serovar Enteritidis must be able to persist inside chicken eggs to be transmitted to humans, and its survival in egg is important for its transmission to the human population. The ability of Salmonella enterica serovar Enteritidis to survive in and transmit through eggs may have contributed to its drastically increased prevalence in the 1980s and 1990s. In the present study, using transposon-mediated mutagenesis, we have identified genes important for the association of Salmonella enterica serovar Enteritidis with chicken eggs. Our results indicate that genes involved in cell wall structural and functional integrity, and nucleic acid and amino acid metabolism are important for Salmonella enterica serovar Enteritidis to persist in egg albumen. Two regions unique to Salmonella enterica serovar Enteritidis were also identified, one of which enhanced the survival of a Salmonella enterica serovar Typhimurium isolate in egg albumen. The implication of our results to the serovar specificity of Salmonella enterica is also explored in the present study