Linoleic acid isomerase was identified as a multi-component enzyme system that consists of three enzymes that exist in both the membrane and soluble fractions of Lactobacillus plantarum. One enzyme (CLA-HY) is present in the membrane fraction, while two enzymes (CLA-DH and CIA-DC) exist in the soluble fraction. Three Escherichia coli transformants expressing CLA-HY. CLA-DH, and CIA-DC were constructed. Conjugated linoleic acid (CIA) and 10-hydroxy-12-octadecenoic acid were generated from linoleic acid only when all these three E. coli transformants were used as catalysts simultaneously. CLA-HY catalyzed the hydration reaction, a part of linoleic acid isomerization, to produce 10-hydroxy-12-octadecenoic acid. This multi-component enzyme system required oxidoreduction cofactors such as NADH and FAD. This is the first report to reveal enzymes genes and the elaborate machinery that synthesizes CIA, especially an important isomer of cis-9, trans-11-CLA, in lactic acid bacteria. (C) 2011 Elsevier Inc. All rights reserved.