Utilization of some D-amino acids by lactobacilli.

As one phase of an investigation of the nutritive requirements of lactobacilli, particularly those from the mouth, the utilization of several D-amino acids was studied. The D-forms used were those of amino acids which, as L-forms, are known to be essential for growth. Earlier studies have shown that the L-forms of valine, leucine, isoleucine, arginine, glutamic acid, aspartic acid (under certain circumstances), tyrosine, phenylalanine, tryptophan, and cyst(e)ine are required by many lactobacilli for growth (for summaries see Dunn, Shankman, Camien and Block, 1947; Dunn, 1949; Koser and Thomas, 1955). The response of lactobacilli and other lactic acid producing bacteria to certain D-amino acids has been studied by a number of investigators who employed a variety of methods, but for the most part the studies dealt with organisms used for microbiological assays. The findings of previous workers which are pertinent will be referred to later in connection with the discussion of results. In the present investigation a collection of lactobacilli, representative of several of the commoner species, was used for a survey of the response to a number of D-amino acids as determined by one method, omitting for the present the more detailed study of utilization of individual amino acids by other means.