A commensal gone bad: complete genome sequence of the prototypical enterotoxigenic Escherichia coli strain H10407.

In most cases, Escherichia coli exists as a harmless commensal organism, but it may on occasion cause intestinal and/or extraintestinal disease. Enterotoxigenic E. coli (ETEC) is the predominant cause of E. coli-mediated diarrhea in the developing world and is responsible for a significant portion of pediatric deaths. In this study, we determined the complete genomic sequence of E. coli H10407, a prototypical strain of enterotoxigenic E. coli, which reproducibly elicits diarrhea in human volunteer studies. We performed genomic and phylogenetic comparisons with other E. coli strains, revealing that the chromosome is closely related to that of the nonpathogenic commensal strain E. coli HS and to those of the laboratory strains E. coli K-12 and C. Furthermore, these analyses demonstrated that there were no chromosomally encoded factors unique to any sequenced ETEC strains. Comparison of the E. coli H10407 plasmids with those from several ETEC strains revealed that the plasmids had a mosaic structure but that several loci were conserved among ETEC strains. This study provides a genetic context for the vast amount of experimental and epidemiological data that have been published.

Deletion of a previously uncharacterized flagellar-hook-length control gene fliK modulates the sigma54-dependent regulon in Campylobacter jejuni.

A previously unannotated, putative fliK gene was identified in the Campylobacter jejuni genome based on sequence analysis; deletion mutants in this gene had a 'polyhook' phenotype characteristic of fliK mutants in other genera. The mutants greatly overexpressed the sigma(54)-dependent flagellar hook protein FlgE, to form unusual filamentous structures resembling straight flagella in addition to polyhooks. The genome sequence reveals only one gene predicted to encode an orthologue of the NtrC-family activator required for sigma(54)-dependent transcription. Hence, all sigma(54)-dependent genes in the genome would be overexpressed in the fliK mutant together with flgE. Microarray analysis of genome-wide transcription in the mutant showed increased transcription of a subset of genes, often downstream of sigma(54)-dependent promoters identified by a quality-predictive algorithm applied to the whole genome. Assessment of genome-wide transcription in deletion mutants in rpoN, encoding sigma(54), and in the sigma(54)-activator gene flgR, showed reciprocally reduced transcription of genes that were overexpressed in the fliK mutant. The fliA (sigma(28))-dependent regulon was also analysed. Together the data clearly define the roles of the alternative sigma factors RpoN and FliA in flagellar biogenesis in C. jejuni, and identify additional putative members of their respective regulons.

Weapons of mass destruction: virulence factors of the global killer enterotoxigenic Escherichia coli.

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of food and water-borne E. coli-mediated human diarrhoea worldwide. The incidence in developing countries is estimated at 650 million cases per year, resulting in 800 000 deaths, primarily in children under the age of five. ETEC is also the most common cause of diarrhoea among travellers, including the military, from industrialized nations to less developed countries. In addition, ETEC is a major pathogen of animals, being responsible for scours in cattle and neonatal and postweaning diarrhoea in pigs and resulting in significant financial losses. Studies on the pathogenesis of ETEC infections have concentrated on the plasmid-encoded heat-stable and heat-labile enterotoxins and on the plasmid-encoded antigenically variable colonization factors. Relatively little work has been carried out on chromosomally encoded virulence factors. Here, we review the known virulence factors of ETEC and highlight the future for combating this major disease.

Mutational and biochemical analysis of cytochrome c', a nitric oxide-binding lipoprotein important for adaptation of Neisseria gonorrhoeae to oxygen-limited growth.

Neisseria gonorrhoeae is a prolific source of c-type cytochromes. Five of the constitutively expressed cytochromes are predicted, based on in silico analysis of the N. gonorrhoeae genome, to be components of the cytochrome bc1 complex, cytochrome c oxidase cbb3 or periplasmic cytochromes involved in electron transfer reactions typical of a bacterium with a microaerobic physiology. Cytochrome c peroxidase was previously shown to be a lipoprotein expressed only during oxygen-limited growth. The final c-type cytochrome, cytochrome c', similar to cytochrome c peroxidase, includes a lipobox required for targeting to the outer membrane. Maturation of cytochrome c' was partially inhibited by globomycin, an antibiotic that specifically inhibits signal peptidase II, resulting in the accumulation of the prolipoprotein in the cytoplasmic membrane. Disruption of the gonococcal cycP gene resulted in an extended lag phase during microaerobic growth in the presence but not in the absence of nitrite, suggesting that cytochrome c' protects the bacteria from NO generated by nitrite reduction during adaptation to oxygen-limited growth. The cytochrome c' gene was overexpressed in Escherichia coli and recombinant cytochrome c' was shown to be targeted to the outer membrane. Spectroscopic evidence is presented showing that gonococcal cytochrome c' is similar to previously characterized cytochrome c' proteins and that it binds NO in vitro. The demonstration that two of the seven gonococcal c-type cytochromes fulfil specialized functions and are outer membrane lipoproteins suggests that the localization of these lipoproteins close to the bacterial surface provides effective protection against external assaults from reactive oxygen and reactive nitrogen species.