SUMMARY: Syntrophism was demonstrated between strains of Lactobacillus plantarum and Streptococcus faecalis in a chemically defined medium which lacked phenylalanine and pteroylglutamic acid (PGA); however, the presence of p-aminobenzoic acid (PABA) was essential. Enumeration of the two organisms in syntrophic growth was found to be possible by the use of Trypticase soy agar + 0·25% (w/v) glucose at pH 9·0 as a selective medium for S. faecalis. It was found that S. faecalis predominated in the early stages of the syntrophic growth, but that L. plantarum eventually predominated. Characterization by a bioautographic technique of the phenylalanine-active factor synthesized by S. faecalis and required by L. plantarum indicated that the factor was not identical with phenylalanine or shikimic acid. Micro-biological assays of the culture fluid from cultures of L. plantarum indicated that three types of folic acid compounds were synthesized: (1) oxygen-stable compounds which supported the growth of Pediococcus cereviseae; (2) oxygen-labile compounds which supported the growth of P. cereviseae; (3) oxygen-stable compounds which supported the growth of S. faecalis but not of P. cereviseae.
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