Bacterial Genes Responsible for the Biosynthesis of Eicosapentaenoic and Docosahexaenoic Acids and Their Heterologous Expression

Until the 1990s, it was thought that, with the exception of cyanobacteria, bacteria had no polyunsaturated fatty acids (PUFAs).This was probably because the bacterial species whose physiology, biochemistry and molecular biology had been well studied until that time were mesophilic species, such as Escherichia coli, which have no PUFAs.It has since been found that n-3 long chain PUFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are preferentially distributed in psychrophilic bacteria that inhabit relatively unusual environments including low temperature, deep-sea environments and the intestines of sea fish (25,31,32).Although several PUFA-producing bacterial strains had been reported until the 1970s (15), the discovery of DHA and EPA in bacteria from deep-sea water and sediments and detailed analysis of them by DeLong and Yayanos in 1986 (2) resulted in the initiation of research into PUFA-producing bacteria.It is interesting that the PUFAs detected in those bacteria were mostly EPA or DHA, and not C18 PUFAs such as linoleic and linolenic acids, which are most common in animals, plants, fungi and cyanobacteria.However, although EPA-and DHA-producing bacteria were discovered in the 1980s, they have not been given much attention.This can easily be imagined as microorganisms (including eukaryotes such as microalgae) with PUFAs such as EPA and DHA are widespread in marine environments (24,25,28).It was also thought that bacterial, as well as eukaryotic, EPA and DHA were biosynthesized by a combination of elongation and oxygen-dependent desaturation of existing fatty acids.Therefore, the successful cloning in 1996 of genes involved in the biosynthesis of EPA from Shewanella sp.SCRC-2738 isolated from marine fish intestines (33) was very important and could be