ABSTRACT
Abstract Obligate anaerobes cannot grow in the presence of atmospheric concentrations of oxygen. It is likely that this deficit is due, in part, to the presence of oxygenlabile targets within the cell. Despite the inability to grow under aerobic conditions, many obligate anaerobes can survive transient exposure to O2 and reactive oxygen species (ROS). In the presence of O2 and ROS, obligately anaerobic Bacteroides species elicit a coordinated response that is essential for survival during periods of oxidative stress. This oxidative stress response (OSR) includes expression of ROS quenching enzymes, such as superoxide dismutase and multiple peroxidases, as well as the DNA protective protein Dps. Similar to other eubacteria, expression of Bacteroides OSR proteins is subject to both OxyR-dependent and OxyR-independent regulation. In addition to the ability to quench ROS, B. fragilis can consume O2 via a cytochrome bd oxidase respiratory chain. In the presence of nanomolar concentrations of O2, this respiratory chain can function in energy metabolism, indicating that the response of this bacterium to O2 is more complex than was previously thought.
