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

Abstract

bCampylobacter jejuni is a food-borne bacterial pathogen that colonizes the intestinal tract and causes severe gastroenteritis. Interaction with host epithelial cells is thought to enhance severity of disease, and the ability of C. jejuni to modulate its metabolism in different in vivo and environmental niches contributes to its success as a pathogen. A C. jejuni operon comprising two genes that we designated fdhT (CJJ81176_1492) and fdhU (CJJ81176_1493) is conserved in many bacterial species. Deletion of fdhT or fdhU in C. jejuni resulted in apparent defects in adherence and/or invasion of Caco-2 epithelial cells when assessed by CFU enumeration on standard Mueller-Hinton agar. However, fluorescence microscopy indicated that each mutant invaded cells at wild-type levels, instead suggesting roles for FdhTU in either intracellular survival or postinvasion recovery. The loss of fdhU caused reduced mRNA levels of formate dehydrogenase (FDH) genes and a severe defect in FDH activity. Cell infection phenotypes of a mutant deleted for the FdhA subunit of FDH and an ⌬fdhU ⌬fdhA double mutant were similar to those of a ⌬fdhU mutant, which likewise suggested that FdhU and FdhA function in the same pathway. Cell infection assays followed by CFU enumeration on plates supplemented with sodium sulfite abolished the ⌬fdhU and ⌬fdhA mutant defects and resulted in significantly enhanced recovery of all strains, including wild type, at the invasion and intracellular survival time points. Collectively, our data indicate that FdhTU and FDH are required for optimal recovery following cell infection and suggest that C. jejuni alters its metabolic potential in the intracellular environment.

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

“…We have shown here the need for selenium for FDH activity and that the Cj1500 (FdhT) and Cj1501 (FdhU) proteins are involved in FDH biogenesis, possibly by mediating selenium uptake or downstream processing. In an independent, concurrent study, Pryjma et al (28) show that in C. jejuni strain 81-176, the fdhTU genes are required for optimal recovery following invasion of epithelial cells, and their data confirm the role of the fdhTU genes in FDH biosynthesis and activity in a third reference strain of C. jejuni. Combined with earlier studies on formate metabolism and intestinal colonization studies and virulence of C. jejuni (2,34,42), this suggests an important contribution of FDH, and also FdhTU and potentially selenium in colonization and virulence properties of C. jejuni.…”

N-Glycosylation of Campylobacter jejuni Surface Proteins Promotes Bacterial Fitness

“…In one such study (32), the C. jejuni genes fdhT and fdhU (encoding the proteins FdhT and FdhU of unknown function) were identified as crucial for the ability to recover these bacteria from standard growth media. Clearly, then, C. jejuni alters its metabolism under different environmental conditions to sustain its pathogenic and commensal modes of existence (32,33). It is possible that cecal proteases may have triggered bacterial switch to a VBNC state, a possible explanation for the reduced pglB mutant CFU recovered despite similar levels of live WT and pglB mutant cells.…”

“…Indeed, it has been shown that C. jejuni can switch into a "viable but nonculturable" (VBNC) state in response to stress (21,31). In recent studies (21,32,33), C. jejuni has been demonstrated to alter its metabolism in response to stress, leading to reduced culturability. In one such study (32), the C. jejuni genes fdhT and fdhU (encoding the proteins FdhT and FdhU of unknown function) were identified as crucial for the ability to recover these bacteria from standard growth media.…”

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

“…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). Altogether, these transcriptomic data demonstrate a role for Cj1000 in the regulation of respiratory pathways that are required for growth under lowoxygen conditions.…”