Differential response of Streptococcus mutans towards friend and foe in mixed-species cultures

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Abstract
In the oral biofilm, the ‘mitis’ streptococci are among the first group of organisms to colonize the tooth surface. Their proliferation is thought to be an important factor required for antagonizing the growth of cariogenic species such asStreptococcus mutans. In this study, we used a three-species mixed culture to demonstrate that another ubiquitous early colonizing species,Veillonella parvula,can greatly affect the outcome of the competition between a pair of antagonists such asS. mutansandStreptococcus gordonii. Transcriptome analysis further revealed thatS. mutansresponds differentially to its friend (V. parvula) and foe (S. gordonii). In the mixed culture withS. gordonii, all but one of theS. mutanssugar uptake and metabolic genes were downregulated, while genes for alternative energy source utilization and H2O2tolerance were upregulated, resulting in a slower but persistent growth. In contrast, when cultured withV. parvula,S. mutansgrew equally well or better than in monoculture and exhibited relatively few changes within its transcriptome. WhenV. parvulawas introduced into the mixed culture ofS. mutansandS. gordonii, it rescued the growth inhibition ofS. mutans. In this three-species environment,S. mutansincreased the expression of genes required for the uptake and metabolism of minor sugars, while genes required for oxidative stress tolerance were downregulated. We conclude that the major factors that affect the competition betweenS. mutansandS. gordoniiare carbohydrate utilization and H2O2resistance. The presence ofV. parvulain the tri-species culture mitigates these two major factors and allowsS. mutansto proliferate, despite the presence ofS. gordonii.
Funding Information
  • COBRE (P20-RR018741-05)
  • Centers of Biomedical Research Excellence
  • NIH (R15 DE019940)

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