Human Serum Supplementation Promotes Streptococcus mitis Growth and Induces Specific Transcriptomic Responses

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.