Role and regulation of fatty acid biosynthesis in the response of Shewanella piezotolerans WP3 to different temperatures and pressures.

Members of the genus Shewanella inhabit various environments; they are capable of synthesizing various types of low-melting-point fatty acids, including monounsaturated fatty acids (MUFA) and branched-chain fatty acids (BCFA) with and without eicosapentanoic acid (EPA). The genes involved in fatty acid synthesis in 15 whole-genome-sequenced Shewanella strains were identified and compared. A typical type II fatty acid synthesis pathway in Shewanella was constructed. A complete EPA synthesis gene cluster was found in all of the Shewanella genomes, although only a few of them were found to produce EPA. The roles and regulation of fatty acids synthesis in Shewanella were further elucidated in the Shewanella piezotolerans WP3 response to different temperatures and pressures. The EPA and BCFA contents of WP3 significantly increased when it was grown at low temperature and/or under high pressure. EPA, but not MUFA, was determined to be crucial for its growth at low temperature and high pressure. A gene cluster for a branched-chain amino acid ABC transporter (LIV-I) was found to be upregulated at low temperature. Combined approaches, including mutagenesis and an isotopic-tracer method, revealed that the LIV-I transporter played an important role in the regulation of BCFA synthesis in WP3. The LIV-I transporter was identified only in the cold-adapted Shewanella species and was assumed to supply an important strategy for Shewanella cold adaptation. This is the first time the molecular mechanism of BCFA regulation in bacteria has been elucidated.