A comparative study on arginine metabolism by oral streptococci revealed both divergence and heterogeneity in dependence on arginine and significance of ornithine and citrulline

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Abstract
Current understanding in arginine metabolism by streptococci is limited in species and strains. We compared the ability of several abundant oral streptococci to synthesize and assimilate arginine. Multiple species of oral streptococci and their genetic mutants were characterized for growth using synthetic media with specified amounts of arginine and related amino acids. Expression of relevant genes was quantified by RT-qPCR. An intact arginine deiminase system (ADS) was required for S. sanguinis to grow with little or no arginine, a capacity substantially hindered by oxygen. Importantly, nearly all oral streptococci tested required arginine, ornithine or citrulline for growth, displaying much heterogeneity. S. mutans, while lacking ADS, grew without exogenous arginine; and presence of ornithine significantly affected its growth dynamics with strain-specific outcomes. Furthermore, loss of an ornithine transcarbamylase in S. mutans abolished ornithine-dependent effects and the ability to synthesize arginine. Expression of biosynthetic arg genes in both S. sanguinis and S. mutans was influenced, albeit differentially, by exogenous arginine, ornithine, oxygen, carbohydrates, and integrity of ADS and the major glucose transporter (EIIMan). Our study suggested that arginine is an essential nutrient for most oral streptococci, excluding S. mutans, and identified ornithine and citrulline as potential metabolic signals in oral microbiome.
Funding Information
  • National Institute of Dental and Craniofacial Research (DE012236)

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