If free Fe2+

is present in the cell, the produced H2O2 can form hydroxyl radicals (·OH), which may directly damage DNA. This may explain the induced production of Dps that reversibly binds iron. The produced H2O2 can be removed by catalase (KatA) which converts H2O2 to H2O and O2[37, 57]. In contrast to a transcriptional study where an up-regulation of katA gene was noticed after acid exposure [24], induction of KatA was not observed in this proteomic study. Since C. jejuni is sensitive towards oxygen and lacks numerous oxidative stress regulators such as SoxRS and OxyR [13], the cell might be in a constantly oxygen-alert state in order to remove reactive oxygen species and damaging components from acid stress. No induction of heat Ferroptosis activation shock proteins (Hsps) as chaperones or proteases were observed during acid stress in this study. A transcriptional study found an up-regulation of clpB, dnaK, grpE, groEL/ES and htrA[24]. One explanation could be the sensitivity of 2D-gel-electrophoresis for proteomic analysis as mentioned selleckchem above and the detection limit due to molecular size and isoelectric point (pI) of the proteins. The Hsps, ClpP and GroES have molecular masses

close to the maximum and minimum detection size, respectively, and HtrA has a pI of 9.6 which is outside the pI range of the system used here. Acid exposure of C. jejuni NCTC 11168 was related to changes in gene expression and synthesis of acid stress proteins. However, comparison of the proteomic and transcription study showed a limited correlation between induced proteins and over-expression of genes. A recent proteomic study with acid adaptation of Salmonella enterica also [26] found a limited correlation between the outcomes of the transcriptional (qRT-PCR) versus translational (2D-gel) studies. The lack of corresponding

results may be due to the lifetime of the RNA and Molecular motor the time from transcription to translation. Conclusions It can be concluded that the three C. jejuni strains, at the phenotypic and proteomic level, responded differently to the acid stresses. We demonstrated that acid stress induces production of several proteins normally involved in iron control and oxidative stress defence in C. jejuni. This work has contributed to the understanding of what occurs in the C. jejuni cells during acid stress. Acknowledgements This work was financially supported by the Danish Food Industry Agency. We acknowledge Bjarne Albrektsen for excellent technical assistance during development and optimization of the chemically defined broth; Andrea Maria Lorentzen from the University of Southern Denmark, who has been a great help in identifying proteins; and Søs Inger Nielsen for excellent technical assistance with qRT-PCR runs. Dr. Thomas Alter, Freie Universitet Berlin, generously provided the strains 305 and 327. References 1. Birk T, Knøchel S: Fate of food-associated bacteria in pork as affected by marinade, temperature, and ultrasound.