Unsaturated fatty acids in microorganisms.

Reports from this laboratory have described the existence of two different pathways for the biosynthesis of long chain monounsaturated fatty acids by microorganisms. In yeast, oleic and palmitoleic acids are formed oxidatively from the corresponding saturated acids by processes requiring molecular oxygen and TPNH (1). The same conversions have been demonstrated in AWycobacterium phlei (2), in the blue-green alga Anabaena variabiQ1 and in Penicillum chrysogenumP The second mechanism for the synthesis of monounsaturated fatty acids, discovered in Clostridium butyricum (3, 4), is anaerobic and produces the olefinic double bonds in the course of the chain-lengthening process rather than by desaturation of the corresponding saturated acids. This nonoxidative pathway appears to be employed not only by the obligate anaerobes but also by various aerobic representatives of the order Eubacteriales. In fungi, plants, and animal tissues, the predominant monounsaturated fatty acids are Ag-hexadecenoic and Ag-octadecenoic acids (5). On the other hand, as first shown by the work of Hofmann, Lucas, and Sax (6), cis-An-octadecenoic acid is the principal monounsaturated acid of lactobacilli species. It was later found also in Aigrobacterium tumejaciens (7), in a species of Group C Streptococcus (8), and in Escherichia coli (9). The purpose of the present investigation was to ascertain whether An-octadecenoic acid is a common constituent of bacterial lipids and whether the double bond structure of unsaturated fatty acids can be related to the mechanism by which they are synthesized. The findings reported in this paper indicate that such a correlation exists. In the course of this work, two monounsaturated fatty acids, not previously described, have been isolated from bacterial sources. Polyunsaturated fatty acids could not be detected in any of the organisms examined.