Regulation of outer-membrane proteins (OMPs) A and F, during hlyF-induced outer-membrane vesicle (OMV) biosynthesis

Gram-negative bacteria actively secrete outer membrane vesicles into the surrounding environment and these vesicles have been shown to play various physiological and protective roles such as carrying antibiotic-degrading enzymes and acting as decoys against host defences, therefore promoting the pathogenesis of the bacterium. It has been shown that avian pathogenic Escherichia coli species can increase vesicle biosynthesis through the acquisition of the hlyF gene but the effect this has on the cell by scavenging outer-membrane associated proteins (OmpA, OmpF) into the vesicles during vesicle release have not yet been investigated.

Relative quantitative real-time PCR data obtained from hlyF expressing and non-expressing cells showed that during hlyF induction, ompF showed a nearly 2-fold down regulation relative to the non-expressing cells during the entire 24 hours, while ompA was expressed at the same level as the non-expressing cells during the first 8 hours of expression. At 24 hours post-hlyF expression, ompA was up-regulated 4-fold.

The regulatory effects of the newly described outer-membrane vesicle biosynthesis-related gene, hlyF, on E. coli has not previously been investigated. As hlyF-induced vesicles contain OmpA and OmpF scavenged from the bacterial outer-membrane, potential regulatory effects on the host was investigated. An increase in ompA expression and an insignificant decrease in ompF expression was observed during hlyF induction demonstrating that hlyF-related biosynthesis is not related to decreased ompA expression, which is one of the potential mechanisms discussed in literature for biosynthesis. Outer-membrane vesicle biosynthesis during hlyF over-expression could potentially be accomplished through a different mechanism(s).