Formate dehydrogenase localization and activity are dependent on an intact twin arginine translocation system (Tat) in campylobacter jejuni 81-176

The oxidation of formate constitutes a main energy source for Campylobacter jejuni, an important foodborne pathogen. Formate occurs in the hosts' gut as a byproduct of fermentation, which may contribute to C. jejuni's adaptation to that niche. C. jejuni possesses a periplasmic formate dehydrogenase (Fdh) that facilitates the metabolism of formate. In C. jejuni NCTC-11168, a poorly invasive strain, Fdh localizes to the periplasm via the twin arginine translocation (Tat) system, and the fdhA encodes the signature Tat signal motif. However, screening the genome of C. jejuni 81-176, a highly invasive strain, showed that the Tat signal motif was encoded on a separate gene (CJJ81176-1504) directly upstream of the fdhA (CJJ81176-1503). This possibly suggested a difference in formate metabolism between these two strains. Therefore, we investigated whether the Fdh was Tat dependent in C. jejuni 81-176. For this purpose, we measured formate respiration in C. jejuni 81-176 (wild-type), a Tat mutant (ΔtatC-81-176), and a complementation strain (C-ΔtatC-81-176) using BIOLOG-AN plates. We also used a viologen-based assay to specifically measure the Fdh enzymatic activity in whole cells and periplasmic preparations of the wild-type and mutant strains. Collectively, our data indicated that the Fdh activity and localization in C. jejuni 81-176 were dependent on a functional Tat system. The proper maturation and maintenance of Fdh are essential for cognate energy production, which might explain the association of the Fdh with the Tat system across different strains. The latter highlights the potential of the Tat system and Fdh as appealing targets for novel anti-C. jejuni therapeutics.