title: Genomic and transcriptomic analyses of the facultative methanotroph Methylocystis sp. strain SB2 grown on methane or ethanol.
abstract: A minority of methanotrophs are able to utilize multicarbon compounds as growth substrates in addition to methane. The pathways utilized by these microorganisms for assimilation of multicarbon compounds, however, have not been explicitly examined. Here, we report the draft genome of the facultative methanotroph Methylocystis sp. strain SB2 and perform a detailed transcriptomic analysis of cultures grown with either methane or ethanol. Evidence for use of the canonical methane oxidation pathway and the serine cycle for carbon assimilation from methane was obtained, as well as for operation of the complete tricarboxylic acid (TCA) cycle and the ethylmalonyl-coenzyme A (EMC) pathway. Experiments with Methylocystis sp. strain SB2 grown on methane revealed that genes responsible for the first step of methane oxidation, the conversion of methane to methanol, were expressed at a significantly higher level than those for downstream oxidative transformations, suggesting that this step may be rate limiting for growth of this strain with methane. Further, transcriptomic analyses of Methylocystis sp. strain SB2 grown with ethanol compared to methane revealed that on ethanol (i) expression of the pathway of methane oxidation and the serine cycle was significantly reduced, (ii) expression of the TCA cycle dramatically increased, and (iii) expression of the EMC pathway was similar. Based on these data, it appears that Methylocystis sp. strain SB2 converts ethanol to acetyl-coenzyme A, which is then funneled into the TCA cycle for energy generation or incorporated into biomass via the EMC pathway. This suggests that some methanotrophs have greater metabolic flexibility than previously thought and that operation of multiple pathways in these microorganisms is highly controlled and integrated.
authors.affiliation: Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Alexey
authors.initials: A
authors.lastname: Vorobev
authors.forename: Sheeja
authors.initials: S
authors.lastname: Jagadevan
authors.forename: Sunit
authors.initials: S
authors.lastname: Jain
authors.forename: Karthik
authors.initials: K
authors.lastname: Anantharaman
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Dick
authors.forename: Stéphane
authors.initials: S
authors.lastname: Vuilleumier
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Semrau
mesh_terms: D052818:Autotrophic Processes; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D002952:Citric Acid Cycle; D000431:Ethanol / Q000378:metabolism*; D023281:Genomics; D008697:Methane / Q000378:metabolism*; D042083:Methylocystaceae / Q000235:genetics* / Q000378:metabolism*; D059467:Transcriptome
chemical_list: D001426:Bacterial Proteins; D000431:Ethanol; D002244:Carbon; D008697:Methane