A marine bacterium, judged as a new species close to Shewanella putrefaciens, was isolated from the intestinal contents of the Pacific mackerel. The isolated strain SCRC-2378 produced eicosapentaenoic acid (EPA) as the sole polyunsaturated fatty acid, which amounted to 24-40% of the total fatty acid in the cell, which corresponded to 2% of dry cell weight. Under the optimal growth conditions (pH 7.0, 20 degrees C, and grown aerobically for 12-18 h), the yield of SCRC-2738 reached 15 g of dry cells/L or 2 x 10(10) viable cells/mL. EPA existed as phospholipid and was found in the sn-2 position of phosphatidylethanolamine and phosphatidylglycerol. The 38 kbp (1,000 base pairs) genome DNA fragment was cloned from SCRC-2738 and expressed in Escherichia coli, which resulted in the production of EPA. The nucleotide sequence of the 38 kbp DNA fragment was determined. The DNA fragment contains eight open reading frames, and three of them possess homology with enzymes involved in fatty acid synthesis. Thus, it may be possible that these EPA biosynthesis genes are applied for EPA production in yeasts or higher plants, and offer a new method for EPA synthesis as new foods containing EPA.