Role of a NosX homolog in Streptococcus gordonii in aerobic growth and biofilm formation

Date
2006
DOI
Authors
Jaafar, Suhailah
Version
OA Version
Citation
Abstract
Streptococcus sanguis, Streptococcus oralis and Streptococcus mitis are among the earliest colonizers of the tooth surface during plaque formation; in addition, these species are associated with extraoral infections, including infective endocarditis. S. gordonii is one of the pioneer bacteria that initiate oral biofilm formation and is one of the mitis group (Kawamura et al., 2003). S. gordonii ::Tn 917-lac biofilm defective mutant was isolated using a biofilm screening assay. Defective mutans were isolated and the expression of the reporter gene was measured by β-galactosidase assays. One of the mutants that were isolated (NosX), part of a putative oxygen stress response (osr), is probably involved in response of the bacteria to oxidative stress. In this study, we want to identify and characterize the effect of the environmental conditions on a biofilm defective mutant and the role of competence in quorum sensing. The mutant used in this study contained a transposon that was inserted in the gene. This transposon encodes for a protein homologous to a Ralstonia eutropha NosX, one of the maturation factors that are required for nitrous oxide reductase. Down stream this gene there are two genes that are encoded for a putative NADPH quinine oxidoreductases, qor1 and qor2. These two genes from a putative oxidative stress response (osr) operon in S. gordonii. Inactivation of NosX results in a defective biofilm. Expression of NosX, measured by β-galactosidase activity of NosX::Tn 917-lac mutant, was growth phase dependent, and enhanced when the mutant was grown under aerobic conditions or in the presence of paraquat. The result of this study suggests the genes involved in resistance to oxygen stress are regulated by the environmental oxygen level.
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Thesis (MSD)--Boston University, Goldman School of Dental Medicine, 2006 (Pediatric Dentistry).
Includes bibliographical references: leaves 52-73.
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