Proteomic Insights into the Molecular Response of Campylobacter jejuni to Acid Shock

Introduction: Campylobacter jejuni is a leading cause of foodborne bacterial gastroenteritis in humans. As C. jejuni transfers from environmental sources into the host gastrointestinal tract, it is exposed to low pH. Survival in an acidic condition may play a critical role on the pathogenesis of C. jejuni.

Purpose: The purpose of this study was to identify differentially expressed proteins that were differentially regulated in response to acid shock.

Methods: C. jejuni NCTC 11168 was exposed to MH broth buffered at pH 7.4 (control) and pH 4.5 for 1 h at 37°C in a microaerophilic chamber. Proteins from control and low pH were extracted and digested. After trypsin-catalyzed ¹⁶O/¹⁸O stable isotope labeling, the peptides from control and acid shock samples were mixed at a 1:1 ratio. The mixture was then analyzed using two-dimensional liquid chromatography coupled online with an LTQ-Orbitrap XL mass spectrometer for MS/MS.

Results: Proteomic analysis revealed that a total of 726 proteins were identified and, among them, 162 proteins, which accounted for approximately 22.3% of the total proteins identified, were significantly changed (over 1.4-fold, P < 0.05) under control and low pH conditions. The differentially expressed proteins (up-regulated, 68 and down-regulated, 94 proteins) are involved in a variety of cellular functions (metabolism, 64, cellular processes and signaling, 26, information storage and processing, 26, and poorly characterized, 13). In 2008, approximately sixty genes of C. jejuni required for growth at low pH were identified by microarray technique (Reid et al, Applied and Environmental Microbiology, 2008, 74(5):1583-97). Out of those genes, twenty-five genes were determined as proteins in this proteome study. Four proteins, glucose-methanol-choline oxidoreductase subunit (cj0415), NADH dehydrogenase subunit L (NuoI), NADH dehydrogenase subunit G (NuoG), and citrate synthase (GltA), were significantly expressed at low pH condition, whereas two proteins, iron-uptake ABC transporter substrate-binding protein (CfbpA) and histidinol dehydrogenase (HisD), were significantly expressed at pH 7.4.        

Significance: For the first time, we investigated the whole proteomic profile of C. jejuni when exposed to low pH. Comparative proteome analysis may provide useful information for the molecular characterization of acid shock response in C. jejuni.