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Sci Rep. 2016 Jun 29;6:28852. doi: 10.1038/srep28852.

Evolutionary inactivation of a sialidase in group B Streptococcus.

Author information

  • 1Department of Oral and Molecular Microbiology, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan.
  • 2Department of Pediatrics School of Medicine, University of California San Diego, La Jolla, CA, USA.
  • 3Department of Urology, Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan.
  • 4Department of Molecular Microbiology and Ob/Gyn, Washington University School of Medicine, St. Louis, Missouri, USA.
  • 5Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, CA, USA.
  • 6Rady Children's Hospital, San Diego, CA, USA.

Abstract

Group B Streptococcus (GBS) is a leading cause of bacterial sepsis and meningitis in newborns. GBS possesses a protein with homology to the pneumococcal virulence factor, NanA, which has neuraminidase (sialidase) activity and promotes blood-brain barrier penetration. However, phylogenetic sequence and enzymatic analyses indicate the GBS NanA ortholog has lost sialidase function - and for this distinction we designate the gene and encoded protein nonA/NonA. Here we analyze NonA function in GBS pathogenesis, and through heterologous expression of active pneumococcal NanA in GBS, potential costs of maintaining sialidase function. GBS wild-type and ΔnonA strains lack sialidase activity, but forced expression of pneumococcal NanA in GBS induced degradation of the terminal sialic acid on its exopolysaccharide capsule. Deletion of nonA did not change GBS-whole blood survival or brain microvascular cell invasion. However, forced expression of pneumococcal NanA in GBS removed terminal sialic acid residues from the bacterial capsule, restricting bacterial proliferation in human blood and in vivo upon mouse infection. GBS expressing pneumococcal NanA had increased invasion of human brain microvascular endothelial cells. Thus, we hypothesize that nonA lost enzyme activity allowing the preservation of an effective survival factor, the sialylated exopolysaccharide capsule.

PMID:
27352769
PMCID:
PMC4926279
DOI:
10.1038/srep28852
[PubMed - in process]
Free PMC Article
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