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Human Serum Supplementation Promotes Streptococcus mitis Growth and Induces Specific Transcriptomic Responses
Yahan Wei1, Camille I Sturges1, Kelli L Palmer1
1Department of Biological Sciences, The University of Texas at Dallas, Richardson, Texas, USA.
Abstract:
Streptococcus mitis is a normal member of the human oral microbiota and a leading opportunistic pathogen causing infective endocarditis (IE). Despite the complex interactions between S. mitis and the human host, understanding of S. mitis physiology and its mechanisms of adaptation to host-associated environments is inadequate, especially compared with other IE bacterial pathogens. This study reports the growth-promoting effects of human serum on S. mitis and other pathogenic streptococci, including S. oralis, S. pneumoniae, and S. agalactiae. Using transcriptomic analyses, we identified that, with the addition of human serum, S. mitis downregulates uptake systems for metal ions and sugars, fatty acid biosynthetic genes, and genes involved in stress response and other processes related with growth and replication. S. mitis upregulates uptake systems for amino acids and short peptides in response to human serum. Zinc availability and environmental signals sensed by the induced short peptide binding proteins were not sufficient to confer the growth-promoting effects. More investigation is required to establish the mechanism for growth promotion. Overall, our study contributes to the fundamental understanding of S. mitis physiology under host-associated conditions. IMPORTANCE S. mitis is exposed to human serum components during commensalism in the human mouth and bloodstream pathogenesis. However, the physiological effects of serum components on this bacterium remain unclear. Using transcriptomic analyses, S. mitis biological processes that respond to the presence of human serum were revealed, improving the fundamental understanding of S. mitis physiology in human host conditions.
Insights
Human serum promotes the growth of Streptococcus mitis, a common oral bacterium and cause of infective endocarditis. Transcriptomic analysis revealed S. mitis alters gene expression in response to serum, impacting nutrient uptake and replication.
Area of Science:
- Microbiology
- Host-Pathogen Interactions
- Bacterial Physiology
Background:
- Streptococcus mitis is a common oral bacterium and a significant cause of infective endocarditis (IE).
- Understanding S. mitis adaptation to host environments is limited compared to other IE pathogens.
- Human serum's physiological effects on S. mitis are largely unknown.
Purpose of the Study:
- To investigate the growth-promoting effects of human serum on S. mitis.
- To elucidate the molecular mechanisms underlying S. mitis adaptation to human serum.
- To compare serum's effects on S. mitis with other pathogenic streptococci.
Main Methods:
- Culturing of S. mitis and related streptococci in human serum.
- Transcriptomic analysis (RNA sequencing) to assess gene expression changes.
- Analysis of nutrient uptake systems and metabolic pathways.
Main Results:
- Human serum significantly promoted the growth of S. mitis, S. oralis, S. pneumoniae, and S. agalactiae.
- S. mitis downregulated metal ion and sugar uptake, fatty acid synthesis, and stress response genes.
- S. mitis upregulated amino acid and short peptide uptake systems in response to serum.
- Zinc availability and short peptide sensing were insufficient to explain growth promotion.
Conclusions:
- Human serum influences S. mitis physiology by altering nutrient acquisition and metabolic processes.
- Further research is needed to fully understand the mechanism of serum-mediated growth promotion.
- This study enhances the fundamental understanding of S. mitis adaptation to host conditions.
