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When pDHA4, a vector carrying all five pfaA-pfaE genes responsible for docosahexaenoic acid (DHA; 22:6) biosynthesis in Moritella marina MP-1, was coexpressed in Escherichia coli with the individual pfaA-pfaD genes for eicosapentaenoic acid (EPA; 20:5) biosynthesis from Shewanella pneumatophori SCRC-2738, both polyunsaturated fatty acids were synthesized only in the recombinant carrying pfaB for EPA synthesis. Escherichia coli coexpressing a deleted construct comprising pfaA, pfaC, pfaD and pfaE for EPA and pfaB for DHA produced EPA and DHA. Both EPA and DHA were detected in bacteria that inherently contained pfa genes for DHA. These results suggest that PfaB is the key enzyme determining the final product in EPA or DHA biosynthesis.

The colony-forming ability of Escherichia coli genetically engineered to produce eicosapentaenoic acid (EPA) grown in 3mM hydrogen peroxide (H(2)O(2)) was similar to that of untreated cells. It was rapidly lost in the absence of EPA. H(2)O(2)-induced protein carbonylation was enhanced in cells lacking EPA. The fatty acid composition of the transformants was unaffected by H(2)O(2) treatment, but the amount of fatty acids decreased in cultures of cells lacking EPA and increased in cultures of cells producing EPA, suggesting that cellular EPA is stable in the presence of H(2)O(2) in vivo and may protect cells directly against oxidative damage. We discuss the possible role of EPA in partially blocking the penetration of H(2)O(2) into cells through membranes containing EPA.

The eicosapentaenoic acid (EPA) synthesis gene cluster isolated from a marine bacterium, Shewanella putrefaciens strain SCRC-2738, was cloned and expressed in the marine cyanobacterium Synechococcus sp. A broad-host-range cosmid vector, pJRD215 (10.2 kb, Smr Kmr), was used to clone a 38 kb insert, pEPA, containing the EPA synthesis gene cluster, creating plasmid pJRDEPA (approx. 48 kb). This plasmid was transferred to the cyanobacterial host at a frequency of 2.2 x 10(-7). Cyanobacterial transconjugants grown at 29 degrees C produced 0.12 mg EPA (g dry weight)-1, whereas those grown at 23 degrees C produced 0.56 mg EPA (g dry weight)-1. The yield was further improved to 0.64 mg (g dry weight)-1 by incubation for 1 d at 17 degrees C. This is believed to be the first successful cloning and expression of such a large heterologous gene cluster in a marine cyanobacterium.