9 research outputs found
The capsule polysaccharide structure and biogenesis for non-O1 Vibrio cholerae NRT36S: genes are embedded in the LPS region
BACKGROUND: In V. cholerae, the biogenesis of capsule polysaccharide is poorly understood. The elucidation of capsule structure and biogenesis is critical to understanding the evolution of surface polysaccharide and the internal relationship between the capsule and LPS in this species. V. cholerae serogroup O31 NRT36S, a human pathogen that produces a heat-stable enterotoxin (NAG-ST), is encapsulated. Here, we report the covalent structure and studies of the biogenesis of the capsule in V. cholerae NRT36S. RESULTS: The structure of the capsular (CPS) polysaccharide was determined by high resolution NMR spectroscopy and shown to be a complex structure with four residues in the repeating subunit. The gene cluster of capsule biogenesis was identified by transposon mutagenesis combined with whole genome sequencing data (GenBank accession DQ915177). The capsule gene cluster shared the same genetic locus as that of the O-antigen of lipopolysaccharide (LPS) biogenesis gene cluster. Other than V. cholerae O139, this is the first V. cholerae CPS for which a structure has been fully elucidated and the genetic locus responsible for biosynthesis identified. CONCLUSION: The co-location of CPS and LPS biosynthesis genes was unexpected, and would provide a mechanism for simultaneous emergence of new O and K antigens in a single strain. This, in turn, may be a key element for V. cholerae to evolve new strains that can escape immunologic detection by host populations
sodC-Based Real-Time PCR for Detection of Neisseria meningitidis
Real-time PCR (rt-PCR) is a widely used molecular method for detection of
Neisseria meningitidis (Nm). Several rt-PCR assays for Nm
target the capsule transport gene, ctrA. However, over
16% of meningococcal carriage isolates lack ctrA,
rendering this target gene ineffective at identification of this sub-population
of meningococcal isolates. The Cu-Zn superoxide dismutase gene,
sodC, is found in Nm but not in other
Neisseria species. To better identify Nm, regardless of
capsule genotype or expression status, a sodC-based TaqMan
rt-PCR assay was developed and validated. Standard curves revealed an average
lower limit of detection of 73 genomes per reaction at cycle threshold
(Ct) value of 35, with 100% average reaction efficiency
and an average R2 of 0.9925. 99.7% (624/626) of Nm isolates
tested were sodC-positive, with a range of average
Ct values from 13.0 to 29.5. The mean sodC
Ct value of these Nm isolates was 17.6±2.2 (±SD).
Of the 626 Nm tested, 178 were nongroupable (NG) ctrA-negative
Nm isolates, and 98.9% (176/178) of these were detected by
sodC rt-PCR. The assay was 100% specific, with all
244 non-Nm isolates testing negative. Of 157 clinical specimens tested,
sodC detected 25/157 Nm or 4 additional specimens compared
to ctrA and 24 more than culture. Among 582 carriage specimens,
sodC detected Nm in 1 more than ctrA and
in 4 more than culture. This sodC rt-PCR assay is a highly
sensitive and specific method for detection of Nm, especially in carriage
studies where many meningococcal isolates lack capsule genes
Independent evolution of the core and accessory gene sets in the genus Neisseria: insights gained from the genome of Neisseria lactamica isolate 020-06
<p>Abstract</p> <p>Background</p> <p>The genus <it>Neisseria </it>contains two important yet very different pathogens, <it>N. meningitidis </it>and <it>N. gonorrhoeae</it>, in addition to non-pathogenic species, of which <it>N. lactamica </it>is the best characterized. Genomic comparisons of these three bacteria will provide insights into the mechanisms and evolution of pathogenesis in this group of organisms, which are applicable to understanding these processes more generally.</p> <p>Results</p> <p>Non-pathogenic <it>N. lactamica </it>exhibits very similar population structure and levels of diversity to the meningococcus, whilst gonococci are essentially recent descendents of a single clone. All three species share a common core gene set estimated to comprise around 1190 CDSs, corresponding to about 60% of the genome. However, some of the nucleotide sequence diversity within this core genome is particular to each group, indicating that cross-species recombination is rare in this shared core gene set. Other than the meningococcal <it>cps </it>region, which encodes the polysaccharide capsule, relatively few members of the large accessory gene pool are exclusive to one species group, and cross-species recombination within this accessory genome is frequent.</p> <p>Conclusion</p> <p>The three <it>Neisseria </it>species groups represent coherent biological and genetic groupings which appear to be maintained by low rates of inter-species horizontal genetic exchange within the core genome. There is extensive evidence for exchange among positively selected genes and the accessory genome and some evidence of hitch-hiking of housekeeping genes with other loci. It is not possible to define a 'pathogenome' for this group of organisms and the disease causing phenotypes are therefore likely to be complex, polygenic, and different among the various disease-associated phenotypes observed.</p