Selenium-Dependent Biogenesis of Formate Dehydrogenase in Campylobacter jejuni Is Controlled by the fdhTU Accessory Genes

Abstract

The food-borne bacterial pathogen Campylobacter jejuni efficiently utilizes organic acids such as lactate and formate for energy production. Formate is rapidly metabolized via the activity of the multisubunit formate dehydrogenase (FDH) enzyme, of which the FdhA subunit is predicted to contain a selenocysteine (SeC) amino acid. In this study we investigated the function of the cj1500 and cj1501 genes of C. jejuni, demonstrate that they are involved in selenium-controlled production of FDH, and propose the names fdhT and fdhU, respectively. Insertional inactivation of fdhT or fdhU in C. jejuni resulted in the absence of FdhA and FdhB protein expression, reduced fdhABC RNA levels, the absence of FDH enzyme activity, and the lack of formate utilization, as assessed by 1 H nuclear magnetic resonance. The fdhABC genes are transcribed from a single promoter located two genes upstream of fdhA, and the decrease in fdhABC RNA levels in the fdhU mutant is mediated at the posttranscriptional level. FDH activity and the ability to utilize formate were restored by genetic complementation with fdhU and by supplementation of the growth media with selenium dioxide. Disruption of SeC synthesis by inactivation of the selA and selB genes also resulted in the absence of FDH activity, which could not be restored by selenium supplementation. Comparative genomic analysis suggests a link between the presence of selA and fdhTU orthologs and the predicted presence of SeC in FdhA. The fdhTU genes encode accessory proteins required for FDH expression and activity in C. jejuni, possibly by contributing to acquisition or utilization of selenium.

FdhTU-Modulated Formate Dehydrogenase Expression and Electron Donor Availability Enhance Recovery ofCampylobacter jejunifollowing Host Cell Infection

“…Transcriptional regulators binding directly upstream of FDH operons have also been identified in other bacteria (54,79), but homologs are not present in C. jejuni. An independent concurrent study by Shaw and coworkers (67) using two different C. jejuni strains demonstrates a requirement for selenium in C. jejuni FDH activity, confirms the importance of FdhTU for FDH function, and suggests that FdhTU modulates FDH-and possibly its expression-via import of selenium which is then, via the Sel pathway, converted to selenocysteine which is required for FdhA synthesis (67). In some organisms, selenium availability has been postulated to affect mRNA stability (47); future work will determine whether this is the case in C. jejuni and also shed light on specific mechanisms by which FdhU affects transcript levels of FDH-related genes.…”

Ecology and Biotechnology of Selenium-Respiring Bacteria

“…Acetate oxidation to hydrogen and subsequent conversion of hydrogen and CO 2 to methane through the syntrophic association between acetate-oxidizing bacteria and hydrogenotrophic methanogens form a dominant methanogenic pathway in anaerobic digesters, particularly in the presence of high concentrations of ammonia and volatile fatty acids (17)(18)(19). Selenium in the form of selenocysteine has been identified in the active site of formate dehydrogenases and is important for formate oxidation (20,21). Accumulation of formate, an intermediate of propionate oxidation, triggers a feedback inhibition resulting in propionate accumulation (22), which may lead to process failure in anaerobic digesters.…”

Inactivation of the LysR regulator Cj1000 of Campylobacter jejuni affects host colonization and respiration

“…Another upregulated gene in the cj1000 mutant strain is cj1500 (2.14-fold, P,0.001). This gene has recently been annotated as fdhT, an accessory gene contributing to formate dehydrogenase expression and activity, probably by interfering with selenium metabolism (Shaw et al, 2012). Interestingly, the fdhTU operon (cj1500-1501) was crucial for recovery after invasion of Caco-2 cells, indicating a major role during infection (Pryjma et al, 2012).…”