Abstract
In many bacteria, OxyR is the major regulator controlling cellular response to H2O2. A common phenotype resulting from OxyR loss is reduced growth rate, but the underlying mechanism is unknown. We demonstrated in Shewanella oneidensis, an important research model for applied and environmental microbes, that the defect is primarily due to an electron shortage to major terminal oxidase cytochrome cbb3. The loss of OxyR leads to enhanced production of electron carriers that compete for electrons against cytochrome cbb3, cytochrome bd in particular. We further showed that the oxyR mutation also results in increased production of menaquinone, an additional means to lessen electrons to cytochrome cbb3. Although regulation of OxyR on these biological processes appears to be indirect, these data indicate that the regulator plays a previously underappreciated role in mediating respiration.
Highlights
Oxidative stress, caused by reactive oxygen species (ROS), including superoxide (O2−), hydrogen peroxide (H2O2), and hydroxyl radical (OH), is one of the unavoidable crises for the vast majority of aerobic organisms by damaging biomolecules such as lipids, proteins and DNA1
We found that the oxyR mutation results in increased production of menaquinone-7, which acts as additional means to lessen electrons to cytochrome cbb[3]
S. oneidensis oxyR mutant is due to H2O2 generated abiotically on LB plates[12,13]
Summary
Oxidative stress, caused by reactive oxygen species (ROS), including superoxide (O2−), hydrogen peroxide (H2O2), and hydroxyl radical (OH), is one of the unavoidable crises for the vast majority of aerobic organisms by damaging biomolecules such as lipids, proteins and DNA1. In Escherichia coli, the model organism in which the oxidative stress response is best understood, and many other bacteria, SoxRS and OxyR, are the predominant regulatory systems mediating cellular response to O2− (redox-cycling compounds) and H2O2, respectively[1]. Shewanella, a group of Gram-negative facultative γ-proteobacteria, inhabit redox-stratified environments and are renowned for their versatile respiratory abilities, which underlies great potential for bioremediation and microbial fuel cells[7] These bacteria are substantially more sensitive to H2O2 than E. coli, in concert with the high susceptibility to UV and ionizing radiation, understandings primarily derived from studies on the model species S. oneidensis[8,9,10,11]. The goal of this study was to address biological factors that are responsible for the growing defect of bacteria, with S. oneidensis as research model. We found that the oxyR mutation results in increased production of menaquinone-7, which acts as additional means to lessen electrons to cytochrome cbb[3]
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