The Extracytoplasmic Function Sigma Factor EcfO Protects <i>Bacteroides Fragilis</i> Against oxidative stress

Bacteroides fragilis encodes a large repertoire of extracytoplasmic (ECF) sigma factors, some of which have been previously demonstrated to respond to oxidative stress. A phylogenetic approach was used to show that one of these, EcfO, and its antisigma factor Reo, are conserved in all of the Bacteroides species. EcfO is a member of the ECF21 family of ECF sigma factors, which have not been studied previously. The EcfO regulon has been identified and is composed of genes coding five novel lipoproteins, a radical SAM-family protein, and the ecfO/reo genes. Gene expression analyses have shown that the EcfO regulon is induced by diverse external cues such as oxidative stress, growth on mucin as carbon source, entry into stationary phase, and growth in vivo. As a first step to identify a function for this regulon, three genes coding for lipoproteins in the NigD family were deleted. However, only a moderate to small defect was observed in the ability to resist free radical stress. Two of these NigD proteins are subject to posttranslational modification by glycosylation and are associated with the membrane. The radical SAM family protein was also examined, and a potential role in posttranslational modification of enzymes involved in the maturation of anaerobic sulfatases is hypothesized. The role of the members of the EcfO regulon potentially provide a finely controlled sensory and response mechanism that facilitates Bacteroides response to extracytoplasmic stress both in and out of the anaerobic colon. This is an important factor that may be necessary for survival in the gut and in the establishment of an abdominal abscess.