When docosahexaenoic acid (DHA)-producing Moritella marina strain MP-1 was cultured in the medium containing 0.5 mu g cerulenin ml(-1), an inhibitor for fatty acid biosynthesis, the cells grew normally, but the content of DHA in the total fatty acids increased from 5.9-19.4%. The DHA yield of M. marina strain MP-1 cells also increased from 4 to 13.7 mg l(-1) by cerulenin treatment. The same effect of cerulenin was observed in eicosapentaenoic acid (EPA)-producing Shewanella marinintestina strain IK-1 grown in the medium containing 7.5 mu g cerulenin ml(-1), and the cerulenin treatment increased the EPA yield from 1.6 to 8 mg l(-1). The use of cerulenin is, therefore, advantageous to increase the content of intracellular polyunsaturated fatty acids (PUFA) in particular PUFA-containing phospholipids in bacterial cells.