Method of producing polyunsaturated fatty acid

A method of producing a polyunsaturated fatty acid in a transgenic bacterium, wherein the polyunsaturated fatty acid is an omega fatty acid, the method comprising steps of:

• (a) introducing a recombinant plasmid into a bacteria cell to obtain the transgenic bacterium, wherein the recombinant plasmid comprises a polycistronic expression system with a polynucleotide encoding one or more elongase and at least two desaturases, wherein the elongase is selected from delta 6 elongase, delta 9 elongase or delta 5 elongase;
• and the desaturase is selected from delta 6 desaturase, delta 8 desaturase, delta 5 desaturase or delta 4 desaturase;
• (b) incubating the transgenic bacterium in a medium containing a fatty acid substrate;
• and
• (c) harvesting the transgenic bacterium and extracting the polyunsaturated fatty acid from the transgenic bacterium.