Abstract: Lactobacillus casei Fx was isolated from cattle rumen for its ability to transform linoleic acid into c9,t11- conjugated linoleic acid (CLA). Genomic DNA was extracted and a 1 700-bp linoleic acid isomerase (LAI) gene fragment was amplified from the strain by PCR. The gene fragment was purified and cloned into the plasmid pUCm-T-LAI to obtain recombinant plasmid pUCm-T-LAI by TA cloning. The recombinant plasmid and the expression plasmid pET-DsbA were subjected to double enzyme digestion and ligated to the recombinant expression vector pET-DsbA-LAI. After identification by PCR and enzymatic digestion, the recombinant expression vector was transformed into E. coli BL21. The recombinant strain, having LAI activity, possessed the ability to specifically transform linoleic acid into c9,t11-CLA isomer. The results showed that the LAI gene from L. casei Fx was successfully cloned. This work makes it possible to understand the difference among the LAI genes in different rumen bacteria.

Key words: conjugated linoleic acid, linoleic acid isomerase, Lactobacillus casei, cloning, expression