Studies of the utilization of C14-labeled octadecenoic acids by Lactobacillus arabinosus.

The ability of long chain unsaturated fatty acids to replace biotin in the nutrition of various members of the genus Lactobacillus has been well established; however, the exact nature of this biotin-fatty acid relationship is in dispute, and a number of conflicting explanations have been suggested for this phenomenon (Nieman, 1954). Williams et al. (1947) were among the first to suggest that in these bacteria biotin may be involved in some way in the biosynthesis of certain indispensable fatty acids, and that when such acids are supplied preformed to the bacteria the biotin requirement is minimized. This concept has come to be widely regarded as the most plausible of the hypotheses thus far advanced to explain the biotinlike activity of unsaturated fatty acids, and has been found to be reconcilable with a variety of experimental observations including antimetabolite effects and the alterations in bacterial lipide spectra caused by changes in the fatty acid content of media (Nieman, 1954; Deuel, 1957; Hofmann et al., 1957). Implicit in and essential to the validity of this hypothesis is the ability of lactobacilli to incorporate into their cells and to further utilize fatty acids supplied in media in lieu of biotin. Until the present time this ability has of necessity been tacitly assumed on the basis of inference from indirect evidence. Although a number of unsaturated fatty acids, of which oleic acid is best known, have been shown to exhibit biotin-replacing capabilities (Axelrod et al., 1948; Kodicek, 1949; Cheng et al., 1951; Hofmann and Panos, 1954; O'Leary and Hofmann, 1957), it has been found that cisvaccenic (cis-11, 12-octadecenoic) acid is the major unsaturated fatty acid component of the cellular lipides of lactobacilli (Hofmann, 1953). This acid has also been shown to possess a marked biotin-replacing capability (Cheng et al., 1951; Hofmann and Panos, 1954). Further studies by