Abstract
C4-dicarboxylates are important molecules for the human pathogen C.jejuni, as they are used as carbon and electron acceptor molecules, as sugars cannot be utilized by this microaerophilic organism. Based on the genome analysis, C. jejuni may possess five different C4–dicarboxylate transporters: DctA, DcuA, DcuB, and two homologs of DcuC. Here, we investigated the regulation and function of various C4–dicarboxylate transporters in C. jejuni. Transcription of the dctA and dcuC homologs is constitutive, while dcuA and dcuB are both directly regulated by the two-component RacR/RacS system in response to limited oxygen availability and the presence of nitrate. The DctA transporter is the only C4-dicarboxylate transporter to allow C. jejuni to grow on C4-carbon sources such as aspartate, fumarate, and succinate at high oxygen levels (10% O2) and is indispensable for the uptake of succinate from the medium under these conditions. Both DcuA and DcuB can sequester aspartate from the medium under low-oxygen conditions (0.3% O2). However, under these conditions, DcuB is the only transporter to secrete succinate to the environment. Under low-oxygen conditions, nitrate prevents the secretion of succinate to the environment and was able to overrule the phenotype of the C4-transporter mutants, indicating that the activity of the aspartate–fumarate–succinate pathway in C. jejuni is strongly reduced by the addition of nitrate in the medium.
Highlights
Bacteria utilize C4-dicarboxylates such as fumarate, succinate, malate, and aspartate when sugars or related compounds are not available (Janausch et al, 2002)
Genome analysis revealed that C. jejuni possesses up to five putative C4-dicarboxylate transporters, DctA, DcuA, DcuB, and some strains contain one or two homologs of the DcuC C4dicarboxylate transporter
The genes dcuB, dcuC, and dctA are not co-transcribed with other genes located in a single-gene operon, while dcuA is located in one operon together with the aspA gene and the dcuC2 gene is located in one operon with C8J_1306 and the metC genes
Summary
Bacteria utilize C4-dicarboxylates such as fumarate, succinate, malate, and aspartate when sugars or related compounds are not available (Janausch et al, 2002). C4-dicarboxylates serve as carbon and energy source and are oxidized to CO2 in the citric acid cycle under aerobic conditions. Malate, and aspartate are taken up into the cell. Malate and aspartate are reduced to fumarate, which is used as electron acceptor in the fumarate respiration pathway where it is converted to succinate. Succinate cannot be further metabolized by most bacteria due to the lack of a functional citric acid cycle under these conditions and is excreted. Despite the medical and public health importance of Campylobacter infection, it is remarkable that C. jejuni is one of the least understood enteropathogens. C. jejuni possesses a highly branched electron transport chain, which allows both
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
