초록
<P>The gene encoding phosphopantetheinyl transferase (PPTase), <I>pfaE</I>, a component of the polyketide synthase (PKS) pathway, is crucial for the production of docosahexaenoic acid (DHA, 22:6ω3), along with the other <I>pfa</I> cluster members <I>pfaA</I>, <I>pfaB</I>, <I>pfaC</I> and <I>pfaD</I>. DHA was produced in <I>Escherichia coli</I> by co-expressing <I>pfaABCD</I> from DHA-producing <I>Colwellia psychrerythraea</I> 34H with one of four <I>pfaE</I> genes from bacteria producing arachidonic acid (ARA, 20:4ω6), eicosapentaenoic acid (EPA, 20:5ω3) or DHA, respectively. Substitution of the <I>pfaE</I> gene from different strain source in <I>E</I>. <I>coli</I> did not influence the function of the PKS pathway producing DHA, although they led to different DHA yields and fatty acid profiles. This result suggested that the <I>pfaE</I> gene could be switchable between these strains for the production of DHA. The DHA production by expressing the reconstituted PKS pathway was also investigated in different <I>E</I>. <I>coli</I> strains, at different temperatures, or with the treatment of cerulenin. The highest DHA production, 2.2 mg of DHA per gram of dry cell weight or 4.1% of total fatty acids, was obtained by co-expressing <I>pfaE</I>(EPA) from the EPA-producing strain <I>Shewanella baltica</I> with <I>pfaABCD</I> in DH5α. Incubation at low temperature (10–15°C) resulted in higher accumulation of DHA compared to higher temperatures. The addition of cerulenin to the medium increased the proportion of DHA and saturated fatty acids, including C12:0, C14:0 and C16:0, at the expense of monounsaturated fatty acids, including C16:1 and C18:1. Supplementation with 1 mg/L cerulenin resulted in the highest DHA yield of 2.4 mg/L upon co-expression of <I>pfaE</I>(DHA) from <I>C</I>. <I>psychrerythraea</I>.</P>