Isolation of AP1, a rumen bacterium that forms 10,12-conjugated linoleic acid.

Some microbes in the rumen form 10,12 (10,12)-conjugated linoleic acid (CLA), a fatty acid that depresses synthesis of milk fat in dairy cattle and other lactating animals. Despite their importance to milk fat depression, the microbes responsible have been difficult to identify, and no laboratory strain is currently available for study. Here we describe the isolation of AP1, a bacterium that forms 10,12-CLA at fast rates. It was isolated from rumen contents of a heifer by using medium containing lactate and metronidazole. It formed 10,12-CLA from linoleic acid, a result confirmed by a combination of 3 methods (spectrophotometry, thin-layer chromatography, and GC). The initial rate of formation was 67% faster than for DSM 1897, the type strain from human skin. The availability of this isolate and its ability to rapidly form 10,12-CLA make it a good subject for further study. Such study could help control formation of 10,12-CLA in the rumen and alleviate milk fat depression in milk cows.