RESUMEN
The bacterial pathogen Campylobacter jejuni is the leading cause of foodborne gastroenteritis in the developed world, with the organism being transmitted by ingestion of contaminated and undercooked poultry. Exposure to acid is an inevitable stressor for C. jejuni during gastric passage, yet the effect of low pH on C. jejuni virulence is still poorly understood. Here, we investigate the effect of acid-shock on C. jejuni viability, gene expression and host-cell invasion. C. jejuni strain NCTC 11168 survived acid exposure at pH 3.5 and above for up to 30 min without a drop in viability, and this exposure induced the expression of flagellar genes transcribed from σ(54)-dependent promoters. Furthermore, acid-shock resulted in increased C. jejuni invasion of m-ICcl2 mouse small intestine crypt cells grown on transwells, but not when the cells were grown on flat-bottomed wells. This suggests that C. jejuni might be invading intestinal epithelial cells at the basolateral side, possibly after paracellular passage. We hypothesize that acid-shock prior to intestinal entry may serve as a signal that primes C. jejuni to express its virulence gene repertoire including flagellar motility genes, but this requires further study in the context of an appropriate colonization or disease model.
RESUMEN
The Escherichia coli Tat system mediates Sec-independent export of protein precursors bearing twin-arginine signal peptides. The essential Tat pathway components TatA, TatB and TatC are shown to be integral membrane proteins. Upon removal of the predicted N-terminal transmembrane helix TatA becomes a water-soluble protein. In contrast the homologous TatB protein retains weak peripheral interactions with the cytoplasmic membrane when the analogous helix is deleted. Chemical crosslinking studies indicate that TatA forms at least homotrimers, and TatB minimally homodimers, in the native membrane environment. The presence of such homo-oligomeric interactions is supported by size exclusion chromatography.