초록
<P>To date, no information has been made available on the genetic traits that lead to increased carbon flow into the fatty acid biosynthetic pathway of <I>Corynebacterium glutamicum</I>. To develop basic technologies for engineering, we employed an approach that begins by isolating a fatty acid-secreting mutant without depending on mutagenic treatment. This was followed by genome analysis to characterize its genetic background. The selection of spontaneous mutants resistant to the palmitic acid ester surfactant Tween 40 resulted in the isolation of a desired mutant that produced oleic acid, suggesting that a single mutation would cause increased carbon flow down the pathway and subsequent excretion of the oversupplied fatty acid into the medium. Two additional rounds of selection of spontaneous cerulenin-resistant mutants led to increased production of the fatty acid in a stepwise manner. Whole-genome sequencing of the resulting best strain identified three specific mutations (<I>fasR20</I>, <I>fasA63</I><SUP>up</SUP>, and <I>fasA2623</I>). Allele-specific PCR analysis showed that the mutations arose in that order. Reconstitution experiments with these mutations revealed that only <I>fasR20</I> gave rise to oleic acid production in the wild-type strain. The other two mutations contributed to an increase in oleic acid production. Deletion of <I>fasR</I> from the wild-type strain led to oleic acid production as well. Reverse transcription-quantitative PCR analysis revealed that the <I>fasR20</I> mutation brought about upregulation of the <I>fasA</I> and <I>fasB</I> genes encoding fatty acid synthases IA and IB, respectively, by 1.31-fold ± 0.11-fold and 1.29-fold ± 0.12-fold, respectively, and of the <I>accD1</I> gene encoding the β-subunit of acetyl-CoA carboxylase by 3.56-fold ± 0.97-fold. On the other hand, the <I>fasA63</I><SUP>up</SUP> mutation upregulated the <I>fasA</I> gene by 2.67-fold ± 0.16-fold. In flask cultivation with 1% glucose, the <I>fasR20 fasA63</I><SUP>up</SUP> <I>fasA2623</I> triple mutant produced approximately 280 mg of fatty acids/liter, which consisted mainly of oleic acid (208 mg/liter) and palmitic acid (47 mg/liter).</P>