title: Incomplete Wood-Ljungdahl pathway facilitates one-carbon metabolism in organohalide-respiring Dehalococcoides mccartyi.
abstract: The acetyl-CoA "Wood-Ljungdahl" pathway couples the folate-mediated one-carbon (C1) metabolism to either CO2 reduction or acetate oxidation via acetyl-CoA. This pathway is distributed in diverse anaerobes and is used for both energy conservation and assimilation of C1 compounds. Genome annotations for all sequenced strains of Dehalococcoides mccartyi, an important bacterium involved in the bioremediation of chlorinated solvents, reveal homologous genes encoding an incomplete Wood-Ljungdahl pathway. Because this pathway lacks key enzymes for both C1 metabolism and CO2 reduction, its cellular functions remain elusive. Here we used D. mccartyi strain 195 as a model organism to investigate the metabolic function of this pathway and its impacts on the growth of strain 195. Surprisingly, this pathway cleaves acetyl-CoA to donate a methyl group for production of methyl-tetrahydrofolate (CH3-THF) for methionine biosynthesis, representing an unconventional strategy for generating CH3-THF in organisms without methylene-tetrahydrofolate reductase. Carbon monoxide (CO) was found to accumulate as an obligate by-product from the acetyl-CoA cleavage because of the lack of a CO dehydrogenase in strain 195. CO accumulation inhibits the sustainable growth and dechlorination of strain 195 maintained in pure cultures, but can be prevented by CO-metabolizing anaerobes that coexist with D. mccartyi, resulting in an unusual syntrophic association. We also found that this pathway incorporates exogenous formate to support serine biosynthesis. This study of the incomplete Wood-Ljungdahl pathway in D. mccartyi indicates a unique bacterial C1 metabolism that is critical for D. mccartyi growth and interactions in dechlorinating communities and may play a role in other anaerobic communities.
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710.
authors.forename: Wei-Qin
authors.initials: WQ
authors.lastname: Zhuang
authors.forename: Shan
authors.initials: S
authors.lastname: Yi
authors.forename: Markus
authors.initials: M
authors.lastname: Bill
authors.forename: Vanessa L
authors.initials: VL
authors.lastname: Brisson
authors.forename: Xueyang
authors.initials: X
authors.lastname: Feng
authors.forename: Yujie
authors.initials: Y
authors.lastname: Men
authors.forename: Mark E
authors.initials: ME
authors.lastname: Conrad
authors.forename: Yinjie J
authors.initials: YJ
authors.lastname: Tang
authors.forename: Lisa
authors.initials: L
authors.lastname: Alvarez-Cohen
mesh_terms: D000106:Acetate-CoA Ligase / Q000235:genetics / Q000378:metabolism; D000085:Acetates / Q000378:metabolism; D000105:Acetyl Coenzyme A / Q000096:biosynthesis; D000332:Aerobiosis; D001421:Bacteria, Anaerobic / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes; D002248:Carbon Monoxide / Q000378:metabolism; D018920:Coculture Techniques; D019295:Computational Biology; D005798:Genes, Bacterial / Q000235:genetics; D054879:Halogenation; D006846:Hydrocarbons, Halogenated / Q000378:metabolism*; D053858:Metabolic Networks and Pathways; D008715:Methionine / Q000096:biosynthesis; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism; D012694:Serine / Q000378:metabolism
chemical_list: D000085:Acetates; D002247:Carbon Isotopes; D006846:Hydrocarbons, Halogenated; D011773:Pyruvates; D012694:Serine; D000105:Acetyl Coenzyme A; D002244:Carbon; D002248:Carbon Monoxide; D008715:Methionine; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D000106:Acetate-CoA Ligase
keywords: 13C isotope analysis; acetyl-CoA synthase; reductive dechlorination
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