Metabolism of conjugated linoleic acids and 18:1 fatty acids by ruminal bacteria: products and mechanisms

Cultures of ruminal bacteria known to metabolize unsaturated fatty acids were grown in medium containing 50 mu g ml(-1) of geometric and positional isomers of conjugated linoleic acid (CLA) or 18: 1 fatty acids and 37.4% deuterium oxide to investigate the mechanisms responsible for fatty acid metabolism. Butyrivibrio fibrisolveris JW11 converted cis-9,trans-11-18: 2 and trans-9,trans-11-18: 2 to trans-11-18: 1 as the main product, labelled at C-9, and metabolized trans-10, cis-12-18 : 2 to trans-10-18: 1, labelled at C-13, and smaller amounts of trans-12-18 : 1 and cis-12-18 : 1. Butyrivibrio proteoclasticus P-18 did not grow in the presence of cis-9,trans-11-18: 2 or trans-10, cis-12-18 : 2, but grew in medium containing trans-9, trans-11-18 : 2, forming 18 : 0. Propionibacterium acnes, a ruminal species that isomerizes linoleic acid to trans-10, cis-12-18: 2, did not metabolize CLA isomers further. B. fibrisolvens metabolized small amounts of trans-10-18: 1, trans-11-18: 1 and cis-9-18 : 1, but the products formed were not detected. B. proteoclasticus, on the other hand, carried out substantial conversion of 18: 1 substrates to 18: 0. P. acnes hydrated cis-9-18 : 1 and trans-11-18: 1 to 10-OH-18: 0, which was further oxidized to yield 10-O-18:0. The deuterium enrichment in the intermediates formed during incubations with 9,111 geometric isomers of CLA was about half that of the products from trans-10, cis-12 CLA and 18: 1 isomers, suggesting that the reduction of 9,11 geometric isomers CLA by ruminal bacteria occurs via different mechanisms compared with the metabolism of other unsaturated fatty acids.