Regulation of Serratia marcescens ompF and ompC porin genes in response to osmotic stress, salicylate, temperature and pH

Abstract

Serratia marcescensis a Gram-negative enterobacterium that has become an important opportunistic pathogen, largely due to its high degree of natural antibiotic resistance. One factor contributing to this natural antibiotic resistance is reduced outer membrane permeability, which is controlled in part by OmpC and OmpF porin proteins. OmpF expression is regulated bymicF, an RNA transcript encoded upstream of theompCgene, which hybridizes with theompFtranscript to inhibit its translation. Regulation ofS. marcescensporin gene expression, as well as that ofmicF, was investigated usingβ-galactosidase reporter gene fusions in response to 5, 8 and 10 % sucrose, 1, 5 and 8 mM salicylate, and different pH and temperature values.β-Galactosidase activity assays revealed that a lower growth temperature (28 °C), a more basic pH (pH 8), and an absence of sucrose and salicylate induce the transcription of theompFgene, whereas the induction ofompCis stimulated at a higher growth temperature (42 °C), acidic pH (pH 6), and maximum concentrations of sucrose (10 %) and salicylate (8 mM). In addition, when multiple conditions were tested, temperature had the predominant effect, followed by pH. In this study, it was found that the MicF regulatory mechanism does not play a role in the osmoregulation of theompFandompCgenes, whereas MicF does repress OmpF expression in the presence of salicylate and high growth temperature, and under low pH conditions.