8 and 3.2 fold) of transcription were observed. This is in agreement with a prior report of decreased transcription of PARP signaling ciaB under starvation stress [10]. HtrA is important for stress tolerance and survival of Gram-negative bacteria as it degrades periplasmic proteins that misfold under stress [36, 37]. HtrA is also important for the virulence of C. jejuni[39, 55–57], and we showed herein that HtrA is important for intra-amoeba survival of C. jejuni by using the htrA mutant (Figure  3). However, limited data are available regarding htrA transcriptional regulation during environmental stress in C. jejuni. Our qRT-PCR results showed that

heat, oxidative and low nutrient stresses only slightly altered htrA transcription. Because the basal level of transcription of htrA is rather high and only limited buy STI571 variations in transcription were observed under stress, the levels of HtrA protein may be sufficient to maintain a proper periplasmic environment under all conditions tested. Surprisingly, osmotic stress heavily repressed the transcription of htrA (~10 fold). Such down-regulation is counter-intuitive since

hyper osmotic stress likely causes aggregation of proteins upon loss of cellular fluids by osmosis. Other stress-response mechanisms may be up-regulated to counter-act the down-regulation of transcription of htrA. Their GSI-IX chemical structure identity is up for debate since C. jejuni does not have the traditional CpX and RseA/B stress response systems

[39]. While the DnaJ chaperone plays a role in C. jejuni thermo-tolerance and in chicken colonization [11, 38], and dnaJ transcription was shown previously to be enhanced under heat stress [12], we did not observe any effect of heat stress on the transcription of dnaJ. This discrepancy is likely due to the very different heat stresses applied. Our study was geared at studying changes occurring during the chain of transmission (change from ambient to chicken temperature of 42°C) and during food processing (warm up to 55°C) as also reported by Gundogdu et al. [13], Urease while available transcriptional studies are more focused on changes occurring during chicken/human host transition (42–37°C variations) [12]. Altogether, although the levels of transcriptional regulation were generally low and varied between the three virulence-associated genes tested, similar trends were observed: up-regulations upon oxidative and heat stress versus down-regulation upon low nutrient and osmotic stresses. This indicates that stress-response mechanisms other than those encoded by the three genes investigated are more important in assisting cells to overcome low nutrient and osmotic stresses. Effect of pre-exposure to stress on uptake of C.