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

Abstract

Cultures of ruminal bacteria known to metabolize unsaturated fatty acids were grown in medium containing 50 μg ml−1of 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 fibrisolvensJW11 convertedcis-9,trans-11-18 : 2 andtrans-9,trans-11-18 : 2 totrans-11-18 : 1 as the main product, labelled at C-9, and metabolizedtrans-10,cis-12-18 : 2 totrans-10-18 : 1, labelled at C-13, and smaller amounts oftrans-12-18 : 1 andcis-12-18 : 1.Butyrivibrio proteoclasticusP-18 did not grow in the presence ofcis-9,trans-11-18 : 2 ortrans-10,cis-12-18 : 2, but grew in medium containingtrans-9,trans-11-18 : 2, forming 18 : 0.Propionibacterium acnes, a ruminal species that isomerizes linoleic acid totrans-10,cis-12-18 : 2, did not metabolize CLA isomers further.B. fibrisolvensmetabolized small amounts oftrans-10-18 : 1,trans-11-18 : 1 andcis-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. acneshydratedcis-9-18 : 1 andtrans-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 9,11 geometric isomers of CLA was about half that of the products fromtrans-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.