Mutations in trans that affect formate dehydrogenase (fdhF) gene expression in Salmonella typhimurium

FdhTU-modulated formate dehydrogenase expression and electron donor availability enhance recovery of Campylobacter jejuni following host cell infection

Campylobacter 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 ΔfdhU ΔfdhA double mutant were similar to those of a ΔfdhU 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 ΔfdhU and ΔfdhA 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.

Genetic map of Salmonella typhimurium, edition VIII

We present edition VIII of the genetic map of Salmonella typhimurium LT2. We list a total of 1,159 genes, 1,080 of which have been located on the circular chromosome and 29 of which are on pSLT, the 90-kb plasmid usually found in LT2 lines. The remaining 50 genes are not yet mapped. The coordinate system used in this edition is neither minutes of transfer time in conjugation crosses nor units representing "phage lengths" of DNA of the transducing phage P22, as used in earlier editions, but centisomes and kilobases based on physical analysis of the lengths of DNA segments between genes. Some of these lengths have been determined by digestion of DNA by rare-cutting endonucleases and separation of fragments by pulsed-field gel electrophoresis. Other lengths have been determined by analysis of DNA sequences in GenBank. We have constructed StySeq1, which incorporates all Salmonella DNA sequence data known to us. StySeq1 comprises over 548 kb of nonredundant chromosomal genomic sequences, representing 11.4% of the chromosome, which is estimated to be just over 4,800 kb in length. Most of these sequences were assigned locations on the chromosome, in some cases by analogy with mapped Escherichia coli sequences.

Cloning and characterization of a gene cluster, phsBCDEF, necessary for the production of hydrogen sulfide from thiosulfate by Salmonella typhimurium

We cloned, by complementation of an H2S- mutant, a cluster of Salmonella typhimurium genes, phsBCDEF, that appears to be essential for the anaerobic production of hydrogen sulfide from thiosulfate. Tn5 mutagenesis and ExoIII deletion analysis showed that approx. the entire region of a 3.3-kb subclone was necessary for H2S production. Subsequent sequencing revealed the presence of five potential translationally coupled open reading frames (ORFs). Their putative protein products were confirmed by synthesis from a phage T7 expression system. Comparison of the encoded sequences with previously determined sequences suggests that these genes constitute part of a thiosulfate-reducing operon coding for a membrane-associated electron transport chain which contains proteins potentially capable of ligating iron-sulfur clusters and heme. Immediately upstream from these genes, a region encoding the C-terminal portion of an ORF (OrfA) was identified that showed a high degree of similarity to some other anaerobic terminal reductases, polysulfide reductase (PsrA) of Wolinella succinogenes and dimethylsulfoxide reductase (DmsA), formate dehydrogenase (formate-hydrogene-lyase linked) (FdhF) and nitrate reductase (NarG) of Escherichia coli.