Influence of hydrophobicity on oligopeptide utilization by oral streptococci

The growth responses of Streptococcus mutans VA-29R, Streptococcus sanguis ATCC 10556, and Streptococcus mitior NIH to hydrophilic and hydrophobic peptides obtained following isopropanol fractionation of Trypticase were compared. Although the two fractions contained peptides of similar molecular size, differences were observed with respect to amino acid compositions. S. mutans VA-29R showed a pronounced difference in growth response to hydrophilic vs. hydrophobic peptides. While growth of this micro-organism on hydrophilic peptides was indistinguishable from that on unfractionated Trypticase, only very slow growth occurred on the hydrophobic peptides. S. sanguis ATCC 10556 and S. mitior NIH also displayed some selectivity, as evidenced by their faster relative growth rates on hydrophilic, as compared with hydrophobic, peptides. The results of this study support the conclusion that the properties of the substrate, as defined by its amino acid composition, may be more important than molecular size as a factor influencing recognition and subsequent utilization of oligopeptides as sources of amino acids for growth by these three oral streptococci.