Submitted to: FEMS Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 27, 2008
Publication Date: April 14, 2008
Citation: Ling, J., Sharma, M., Bhagwat, A.A. 2008. The role of RNA polymerase sigma-factor (RpoS) in induction of glutamate-dependent acid-resistance of Escherichia albertii under anaerobic conditions. FEMS Microbiology Letters. 283:75-82.
Interpretive Summary: Escherichia alberii, a close relative of E. coli O157:H7, has been identified as an emerging food-borne pathogen and has been implicated in outbreaks of diarrhea among children. An in-depth biochemical and physiological characterization of this pathogen is needed for its successful identification. Comparative genetic analyses of E. albertii and E. coli O157:H7 strains were conducted and a unique regulatory pathway was identified in E. albertii which enabled it to withstand gastric acidity. Understanding the acid tolerance pathways will advance our knowledge of how enteric human pathogens survive on acidic produce such as apple cider and orange juice. This research will benefit the fresh produce industry as well as increasing the microbial food safety of the American food supply.
Escherichia albertii is a potential enteric foodborne 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 two acid-resistance pathways in five E. albertii strains that have been identified so far. We observed that the strains were unable to induce a glutamate-dependent acid-resistance pathway (GDAR) under aerobic growth conditions. Mobilization of the rpoS gene restored aerobic induction of GDAR indicating that all 5 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 Escherichia coli O157:H7 strains), 3 out 5 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.