No abstract

Branched-chain fatty acids of the iso and anteiso series occur in many bacteria as the major acyl constituents of membrane lipids. In addition, omega-cyclohexyl and omega-cycloheptyl fatty acids are present in several bacterial species. These two types of fatty acids are synthesized by the repeated condensation of malonyl coenzyme A with one of the branched-chain and cyclic primers by the same enzyme system. The pathway of de novo branched-chain fatty acid synthesis differs only in initial steps of synthesis from that of the common straight-chain fatty acid (palmitic acid) present in most organisms. The cell membranes composed largely of iso-, anteiso-, and omega-alicyclic acids support growth of bacteria, which inhabit normal as well as extreme environments. The occurrence of these types of fatty acids as major cellular fatty acids is an important criterion used to aid identification and classification of bacteria.

nally methyl-branched fatty acids, 13-methyltetradecanoic (iso-C15) and 15-methylhexadecanoic (iso-C,7), in Bacillus subtilis (natto) (138), and 12-methyltetradecanoic (anteiso-C,5) acid in a species of Sarcina (4), was first reported. After these reports, extensive studies conducted in my laboratory led to the discovery of three additional branched-chain fatty acids; 12methyltridecanoic (iso-C14), 14-methylpentadecanoic (iso-C16), and 14-methylhexadecanoic (anteiso-C,7) acids in the lipids of B. subtilis (76). These branched-chain acids are grouped in three series, based on their biosynthetic relationships (28, 77, 79, 80, 92, 102, 119) (Fig. 1). The definitions of iso and anteiso permit only iso methyl-substituted fatty acids (an iso ethyl would be an anteiso methyl of one-higher chain number), but would allow both methyl and ethyl as anteiso substitutions. Only the methyl anteiso substituent has so far been found in 391

Fatty acids produced by 22 strains of 10 species of the genus Bacillus were analyzed on a very efficient and selective gas-liquid chromatographic column. All of the 10 species, alvei, brevis, cereus, circulans, licheniformis, macerans, megaterium, polymyxa, pumilus, and subtilis, produced eight fatty acids, six branched (anteiso-C15, anteiso-C17, iso-C14, iso-C15, iso-C16, and iso-C17) and two normal (n-Cl4 and n-C16). In all cases, the six branched-chain fatty acids made up over 60% of the total fatty acids. In addition to the eight fatty acids, B. cereus produced four extra fatty acids, three branched (anteiso-C13, iso-C12, and iso-C13) and one monoenoic-n-CI6. Furthermore, there were distinct differences in the relative amounts of fatty acids produced between B. cereus and the remaining nine species. B. cereus produced iso-C15 fatty acid in the largest amount on a glucose-yeast extract medium as well as on Pennassay Broth. On the other hand, for the remaining nine species, anteiso-C15 fatty acid was the major fatty acid from the glucose-yeast extract medium, whereas the amount of iso-C15 fatty acid from Penassay Broth became comparable to that of anteiso-C15 fatty acid. Mechanisms and various factors affecting the fatty acid distribution pattern in the 10 Bacillus species are discussed.

The fatty acids produced by Bacillus subtilis may be grouped into four pairs: 12-methyltetradecanoic and 14-methylhexadecanoic acids (anteiso-Cis and anteiso-Clr), 13-methyltetradecanoic and 15-methylhexadecanoic acids (ko-Cis and iso-Clr), 12-methyltridecanoic and 14-methylpentadecanoic acids (ISO-Cir and iso-CIe), and myristic and palmitic acids (n-Clc and n-Cis). Any one of the branched-chain amino acids, L-isoleucine, L-leucine, or L-valine, or of the branched short-chain fatty acids, a-methylbutyrate, isovalerate, or isobutyrate, added to the glucose -yeast extract medium increased the synthesis of the specific pairs of fatty acids structurally related to the added substrate and decreased the synthesis of other fatty acids. This indicates that the relative abundance of branched-chain fatty acids in B. subtilis is a function of the relative availability of the precursors of the terminal portions of the fatty acids, presumably amethylbutyryl-CoA, isovaleryl-CoA, and isobutyryl-CoA. This mechanism is consistent with the relative abundances of branched-chain fatty acids found in mutants of B. subtilis which require particular branched-chain amino acids. The biotin content of the culture medium and the length of incubation time also affected the relative abundance of the fatty acids.