Production of trans-10, cis-12 conjugated linoleic acid by Megasphaera eisdenii YJ-4:: Physiological roles in the rumen

Megaspahera elsdenii YJ-4, which was previously isolated as a producer of trans-10, cis-12 CLA, was studied for its carbon source on the CLA production. M. elsdenii YJ-4, was incubated with glucose and lactose, and cultured in batch and continuous culture systems with linoleic acid at various pHs to investigate CLA production. Batch cultures of the ruminal bacterium, M. elsdenii YJ-4, were resistant to stearic acid and linoleic acid, and little growth inhibition was observed even when the fatty acid concentration in the culture was as much as 4 mg ml(-1). Stationary phase batch cultures (0.25 mg bacterial protein ml(-1)) that had been grown on lactate and incubated with linoleic acid (0.20 mg ml(-1)) produced approximately 12 mu g trans-10, cis-12 CLA mg protein(-1) and little cis-9, trans-11 CLA was detected. Some linoleic acid was converted to hydrogenated products (chiefly stearic acid), but these fatty acids were less than 5 mu g mg bacterial protein-'. Stationary phase batch cultures that had been grown on glucose produced at least 3-fold less trans-10, cis-12 CLA than ones grown on lactate. Cells from lactate-limited continuous cultures produced less trans-10, cis-12 CLA than those from batch culture, but only if the pH was greater than 6.4. When the pH of the lactate-limited continuous cultures was lower than 6.4, trans-10, cis-12 CLA and hydrogenated products declined. Cells from glucose-limited continuous cultures produced less trans-10, cis-12 CLA and hydrogenated products than the cells that had been limited by lactate, but pH had little impact on this production. These results support the idea that M. elsdenii YJ-4 could be one of the major producers of trans-10, cis-12 CLA which causes cows to produce milk with a low fat content.