Role of RNA polymerase sigma-factor (RpoS) in induction of glutamate-dependent acid-resistance of Escherichia albertii under anaerobic conditions.

Escherichia albertii is a potential enteric food-borne pathogen with poorly defined genetic and biochemical properties. Acid resistance is perceived to be an important property of enteric pathogens, enabling them to survive passage through stomach acidity so that they may colonize the mammalian gastrointestinal tract. We analyzed glutamate-dependent acid-resistance pathway (GDAR) in five E. albertii strains that have been identified so far. We observed that the strains were unable to induce GDAR under aerobic growth conditions. Mobilization of the rpoS gene restored aerobic induction of this acid-resistance pathway, indicating that all five strains may have a dysfunctional sigma-factor. On the other hand, under anaerobic growth conditions where GDAR is induced in an RpoS-independent manner (i.e. in Shigella spp. and Escherichia coli O157:H7 strains), only three out of five E. albertii strains successfully induced GDAR. The remainder of the two strains exhibited dependence on functional RpoS even under anaerobic conditions to express GDAR, a regulatory function previously considered to be redundant. The data indicate that certain E. albertii strains may have an alternate RpoS-dependent pathway for acid-resistance under anaerobic growth conditions.