Effect of D-amino acids on growth of lactobacilli.

It has been shown (Hier et al., 1944; Graham et al., 1950; Rusell et al., 1952; Teeri and Joselyn, 1953) that an unusually high concentration of a single amino acid in the diet or medium may cause growth repression, even though it may be an essential amino acid. Suggestions have been made that such repression may be due to amino acid imbalance (Hier et al., 1944) or that it may be a characteristic property of the specific amino acid (Russell et al., 1952). It is interesting to note that this effect has occurred often with D(or DL-) amino acids, a fact which invites speculation that it may be due to the less commonly utilized D-isomer. For example, it has been shown (Hegsted, 1945) that in the absence of L-leucine, D-leucine allows some growth of Lactobacillus arabinosus although the rate is muchbelownormal. Alsousing this same organism (Hegsted, 1944) it was concluded that D-valine is completely inactive and furthermore does not inhibit the response of DL-valine. Preliminary experiments in connectionwith the studyreported herein indicated that D-valine does inhibit the response of DL-valine. This difference in results probably is explained by the fact that a much higher concentration of the D-amino acid was used in the latter case. Other studies (Fox et al., 1944; Fling and Fox, 1945; Kobayashi et al., 1949; Yaw and Kakavas, 1952) have shown inhibitory effects by some D-amino acids on the growth of L. arabinosus, Escherichia coli, and Brucella abortus. Although, as indicated above, there have been reports indicating the lack of availability of one of the two enantiomorphs of an amino acid for growth, there are no examples which demonstrate whether ornota true competitive inhibition is involved. This investigation has been undertaken, therefore, to study the effects of D-amino