title: Widespread occurrence of secondary lipid biosynthesis potential in microbial lineages.
abstract: Bacterial production of long-chain omega-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), is constrained to a narrow subset of marine γ-proteobacteria. The genes responsible for de novo bacterial PUFA biosynthesis, designated pfaEABCD, encode large, multi-domain protein complexes akin to type I iterative fatty acid and polyketide synthases, herein referred to as "Pfa synthases". In addition to the archetypal Pfa synthase gene products from marine bacteria, we have identified homologous type I FAS/PKS gene clusters in diverse microbial lineages spanning 45 genera representing 10 phyla, presumed to be involved in long-chain fatty acid biosynthesis. In total, 20 distinct types of gene clusters were identified. Collectively, we propose the designation of "secondary lipids" to describe these biosynthetic pathways and products, a proposition consistent with the "secondary metabolite" vernacular. Phylogenomic analysis reveals a high degree of functional conservation within distinct biosynthetic pathways. Incongruence between secondary lipid synthase functional clades and taxonomic group membership combined with the lack of orthologous gene clusters in closely related strains suggests horizontal gene transfer has contributed to the dissemination of specialized lipid biosynthetic activities across disparate microbial lineages.
authors.affiliation: Division of Biological Sciences, University of California San Diego, La Jolla, California, United States of America.
authors.forename: Christine N
authors.initials: CN
authors.lastname: Shulse
authors.forename: Eric E
authors.initials: EE
authors.lastname: Allen
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D004281:Docosahexaenoic Acids / Q000378:metabolism; D015118:Eicosapentaenoic Acid / Q000378:metabolism; D064429:Fatty Acid Synthases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D016013:Likelihood Functions; D005810:Multigene Family / Q000235:genetics / Q000502:physiology; D010802:Phylogeny; D048630:Polyketide Synthases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D014733:Vibrio / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004281:Docosahexaenoic Acids; D048630:Polyketide Synthases; D015118:Eicosapentaenoic Acid; D064429:Fatty Acid Synthases