Genetic Diversity of O-Antigen Biosynthesis Regions in Vibrio cholerae

Abstract

O-antigen biosynthetic (wbf) regions for Vibrio cholerae serogroups O5, O8, and O108 were isolated and sequenced. Sequences were compared to those of other published V. cholerae O-antigen regions. These wbf regions showed a high degree of heterogeneity both in gene content and in gene order. Genes identified frequently showed greater similarities to polysaccharide biosynthesis genes from species other than V. cholerae. Our results demonstrate the plasticity of O-antigen genes in V. cholerae, the diversity of the genetic pool from which they are drawn, and the likelihood that new pandemic serogroups will emerge.Cholera is a pandemic diarrheal disease that continues to be an important cause of morbidity and mortality worldwide. Cholera is associated with a clonally related subset of Vibrio cholerae strains, which carry ctxAB (cholera toxin subunits A and B), the vibrio pathogenicity island (VPI), and other cholera-associated genes (15,40). Until 1992, only serogroup O1 (out of more than 206 serogroups currently described) was recognized as a cause of cholera. In 1992, a new, non-O1 V. cholerae strain (subsequently designated V. cholerae O139) appeared in India and rapidly spread across much of Asia (32). Extensive studies (5,12,31,41) demonstrated that the O139 strain was closely related to the O1 El Tor strains of the 7th pandemic, except that the genes responsible for O1-antigen biosynthesis were deleted and replaced with DNA that encodes the O139 antigen. Since the O antigen is the major protective epitope, its alteration was sufficient to allow O139 strains to move in epidemic form through populations previously immune to cholera caused by O1. Thus, adults were more commonly affected than children (1). Recent studies suggest that the pandemic cluster carries other serogroups as well, including O37, O27, O53, O65, and O75 (31, 40, 43). These observations are consistent with the hypothesis that pathogenic V. cholerae strains are able to easily acquire and/or exchange O-antigen genes, with the new O antigen allowing strains to evade preexisting immunity to cholera.Changes in O-antigen structure also may provide selective advantages in the environment. During epidemics, bacteriophage may play a crucial role in controlling the number of V. cholerae in the environment (19), and since the O-antigen may serve as bacteriophage receptors, serogroup conversion also may be beneficial for evading phage predation (33). It is well documented that mobile genetic elements, bacteriophage, and the competence of V. cholerae to take up and assimilate free DNA from the environment significantly contribute to genetic diversity in V. cholerae (18). Serogroup conversion was demonstrated while V. cholerae was growing on a chitin substrate (6). This transfer may have been facilitated by the JUMPstart sequence, which has nucleotide similarity to a DNA uptake signal that causes the preferential uptake of free DNA containing that sequence in the Pasteurellaceae and is present in front of a laterally transferred O-antigen region in V. chole...

Extended-spectrum β-lactamase, shigatoxin and haemolysis capacity of O157 and non-O157 E. coli serotypes from producer-distributor bulk milk

“…Sizes of amplified rfb gene region fragments for the isolates which ranged from 0.2 -2 kbp (Fig 2) were far lower than what was reported by Coimbra et al (2000). This could be as a result of the plasticity of O-antigen genes in E. coli and more so, the diversity of the genetic pool in different geographical regions (Aydanian, Tang, Morris, Johnson, & Stine, 2011). Restriction digestion using MboII generated O-patterns with less than 30 band fragments.…”

Is the pan-genome also a pan-selectome?

“…The O-chain is a repeat-unit polysaccharide, the monomeric repeat has generally between two and six sugar residues. O-chains are extremely variable in the nature, order and linkage of the different sugars 13, 16 . This complex polysaccharide is very important for the survival of the cell, providing the appropriate hydrophilic envelope to allow nutrient imports towards the cell 17 .…”

Progress in understanding the assembly process of bacterial O-antigen

“…Interestingly, in P. aeruginosa, both pathways of O-antigen biogenesis operate in parallel (Kintz & Goldberg, 2008;Lam et al, 2011). Recently, sequencing of the Vibrio de O31 genome also revealed the presence of both gene clusters in this microorganism (Aydanian et al, 2011). Recently, sequencing of the Vibrio de O31 genome also revealed the presence of both gene clusters in this microorganism (Aydanian et al, 2011).…”

“…The Wzydependent pathway gives rise to the serotype-specific O-antigen known as the B-band while the ABC transporter mediating the assembly of the common antigen is referred to as the A-band, giving rise to two populations of LPS molecules, which coexist in the same cell (Lam et al, 2011). Recently, sequencing of the Vibrio de O31 genome also revealed the presence of both gene clusters in this microorganism (Aydanian et al, 2011).…”