The Campylobacter concisus BisA protein plays a dual role: oxide-dependent anaerobic respiration and periplasmic methionine sulfoxide repair

d-aspartate, an amino-acid important for human health, supports anaerobic respiration in several Campylobacter species

Despite being classified as microaerophilic microorganisms, most Campylobacter species can grow anaerobically, using formate or molecular hydrogen (H2) as electron donors, and various nitrogenous and sulfurous compounds as electron acceptors. Herein, we showed that both l-asparagine (l-Asn) and l-aspartic acid (l-Asp) bolster H2-driven anaerobic growth in several Campylobacter species, whereas the d-enantiomer form of both asparagine (d-Asn) and aspartic acid (d-Asp) only increased anaerobic growth in Campylobacter concisus strain 13826 and Campylobacter ureolyticus strain NCTC10941. A gene annotated as racD encoding for a putative d/l-Asp racemase was identified in the genome of both strains. Disruption of racD in Cc13826 resulted in the inability of the mutant strain to use either d-enantiomer during anaerobic growth. Hence, our results suggest that the racD gene is required for campylobacters to use either d-Asp or d-Asn. The use of d-Asp by various human opportunistic bacterial pathogens, including C. concisus, C. ureolyticus, and also possibly select strains of Campylobacter gracilis, Campylobacter rectus and Campylobacter showae, is significant, because d-Asp is an important signal molecule for both human nervous and neuroendocrine systems. To our knowledge, this is the first report of pathogens scavenging a d-amino acid essential for human health.

Investigation of Campylobacter concisus gastric epithelial pathogenicity using AGS cells

Campylobacter concisus is an oral bacterium. Recent studies suggest that C. concisus may be involved in human gastric diseases. The mechanisms, however, by which C. concisus causes human gastric diseases have not been investigated. Here we examined the gastric epithelial pathogenicity of C. concisus using a cell culture model. Six C. concisus strains and the human gastric epithelial cell line AGS cells were used. IL-8 produced by AGS cells after incubation with C. concisus was measured using enzyme-linked immunosorbent assay (ELISA), and AGS cell apoptosis was determined by caspase 3/7 activities. The effects of C. concisus on actin arrangement in AGS cells was determined using fluorescence staining. The effects of C. concisus on global gene expression in AGS cells was determined by transcriptomic analysis and quantitative real-time PCR (qRT-PCR). The role of the upregulated CYP1A1 gene in gastric cancer survival was assessed using the Kaplan-Meier method. C. concisus induced production of IL-8 by AGS cells with strain variation. Significantly increased caspase 3/7 activities were observed in AGS cells incubated with C. concisus strains when compared to AGS cells without bacteria. C. concisus induced actin re-arrangement in AGS cells. C. concisus upregulated 30 genes in AGS cells and the upregulation of CYP1A1 gene was confirmed by qRT-PCR. The Kaplan-Meier analysis showed that upregulation of CYP1A1 gene is associated with worse survival in gastric cancer patients. Our findings suggest that C. concisus may play a role in gastric inflammation and the progression of gastric cancer. Further investigation in clinical studies is warranted.