Environmental Regulation of Campylobacter jejuni Major Outer Membrane Protein Porin Expression in Escherichia coli Monitored by Using Green Fluorescent Protein

Abstract

ABSTRACT Porins allow exchanges between bacteria and their environment. In the gram-negative food-borne pathogen Campylobacter jejuni two porins, major outer membrane protein (MOMP) and Omp50, have been identified. MOMP is synthesized at a very high level under laboratory culture conditions, suggesting that its promoter functions very efficiently under these conditions. In Campylobacter samples, we observed that MOMP porin expression increased at a high temperature (42°C) or a high pH (pH 8.5) compared to expression at a low temperature (31°C) or an acidic pH (pH 5.5). To study the regulation of MOMP expression at the transcriptional level, we constructed an momp-gfp fusion in which gfp expression was put under the control of the momp promoter. Interestingly, we observed the same pattern of regulation in Escherichia coli , as monitored by green fluorescent protein production, that was found in Campylobacter . The ranges of pH and temperature tested are physiologically relevant, because they can be found in the digestive tracts of both birds and humans, which are both colonized by Campylobacter. Our results suggest that a component of the regulatory mechanism is conserved in C. jejuni and E. coli . However, medium osmolarity and sodium salicylate did not have a significant effect on C. jejuni momp promoter activity in E. coli , suggesting that major regulatory elements of E. coli porin expression do not participate in MOMP regulation. In contrast, mechanisms involving DNA supercoiling may be involved, as shown by DNA gyrase inhibition assays. These findings are a step towards determining the role of outer membrane proteins in the adaptation of C. jejuni to its environment.