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Characterization of putative sialidase genes in Gardnerella vaginalis



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Gardnerella vaginalis is a hallmark organism in the dysbiosis bacterial vaginosis (BV) in reproductive age women although its role in this condition is not currently understood. Diversity within G. vaginalis in terms of virulence factors such as sialidase activity, may explain why it is also observed in asymptomatic women. This thesis aimed to identify genomic determinants of sialidase activity in G. vaginalis and better understand its role in BV. G. vaginalis has demonstrated genotypic and phenotypic diversity in research over the years and has been divided into four subgroups (A-D) based on cpn60 universal target sequencing. Recent research has demonstrated that a previously identified sialidase gene (Gene 1) does not correlate with sialidase activity. Analysis of 39 available G. vaginalis genome sequences identified a second sialidase gene (Gene 2), and its presence correlated with sialidase activity in 112 G. vaginalis isolates. Based on examination of the predicted amino acid sequences of the two sialidases, we hypothesized that Gene 1 encodes an intracellular sialidase while Gene 2 encodes an extracellular sialidase found almost exclusively in subgroup B strains. Gene 1 was shown to encode for a sialidase enzyme with a pH optimum of 4.5 to 5.0. No protein could be expressed from Gene 2 in E. coli. A homopolymer region was identified in Gene 2 that caused an early stop codon, and may be involved in slipped-strand mispairing. When sialidase activity was assayed in cultures of sialidase activity positive (Gene 2 positive) and negative (Gene 2 negative) isolates, activity was detected only in the cell pellet of Gene 2 positive isolates, suggesting that Protein 2 is a cell bound, extracellular sialidase. The results of this thesis demonstrate that G. vaginalis has at least two sialidase genes, only one of which encodes the extracellular sialidase activity observed in some isolates. This may help explain why G. vaginalis is found in women with symptomatic BV, as well as women with no signs of dysbiosis. The finding that extracellular sialidase activity is confined to subgroup B G. vaginalis suggests that these isolates may have an important role in the establishment and maintenance of vaginal dysbiosis.



Bacterial vaginosis, BV, sialidase, Gardnerella vaginalis, characterization



Master of Science (M.Sc.)


Veterinary Microbiology


Veterinary Microbiology


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