Project description:Isoprene-metabolizing bacteria represent a global regulator for atmospheric isoprene concentrations. Under anoxic conditions, isoprene can be used as an electron acceptor reducing it to methylbutene. This study describes the proteogenomic profiling of an isoprene reducing enrichment culture to identify organisms and genes responsible for the isoprene hydrogenation reaction. A metagenome assembled genome (MAG) of the most abundant (88 % rel. abundance) lineage in the enrichment, Acetobacterium wieringae, was obtained. Comparative proteogenomics and RT-PCR identified a five-gene operon from the A. wieringae MAG upregulated during isoprene reduction. The operon encodes a putative oxidoreductase, three pleiotropic nickel chaperones (HypA, HypA, HypB) and one 4Fe-4S ferredoxin. The oxidoreductase is proposed as the putative isoprene reductase with a binding site for NADH, FAD as well as two pairs of [4Fe-4S]-clusters. Other Acetobacterium strains (A. woodii DSM 1030, A. wieringae DSM 1911, A. malicum DSM 4132 and A. dehalogenans DSM 11527) do not encode the isoprene reduction operon and could not reduce isoprene. Uncharacterized homologs of the putative isoprene reductase are observed across the Firmicutes, Spirochaetes, Tenericutes, Actinobacteria, Chloroflexi, Bacteroidetes and Proteobacteria, suggesting the ability of biohydrogenation of non-functionalized conjugated doubled bonds in other unsaturated hydrocarbons.
Project description:Ruminiclostridium thermocellum DSM 1313 strain adhE*(EA) expression was studied along with ∆hydG and ∆hydG∆ech mutants strains deposited under GSE54082. All strains have been described in a study entitled Elimination of hydrogenase post-translational modification blocks H2 production and increases ethanol yield in Clostridium thermocellum. Biswas, et .al. Biotechnology for Biofuels 2015 8:20 Ruminiclostridium (Clostridium) thermocellum is a leading candidate organism for implementing a consolidated bioprocessing (CBP) strategy for biofuel production due to its native ability to rapidly consume cellulose and its existing ethanol production pathway. C. thermocellum converts cellulose and cellobiose to lactate, formate, acetate, H2, ethanol, amino acids, and other products. Elimination of the pathways leading to products such as H2 could redirect carbon flux towards ethanol production. Rather than delete each hydrogenase individually, we targeted a hydrogenase maturase gene (hydG), which is involved in converting the three [FeFe] hydrogenase apoenzymes into holoenzymes by assembling the active site. This functionally inactivated all three Fe-Fe hydrogenases simultaneously, as they were unable to make active enzymes. In the ∆hydG mutant, the [NiFe] hydrogenase-encoding ech was also deleted to obtain a mutant that functionally lacks all hydrogenase. The ethanol yield increased nearly 2-fold in ∆hydG∆ech compared to wild type, and H2 production was below the detection limit. Interestingly, ∆hydG and ∆hydG∆ech exhibited improved growth in the presence of acetate in the medium. Transcriptomic and proteomic analysis reveal that genes related to sulfate transport and metabolism were up-regulated in the presence of added acetate in ∆hydG, resulting in altered sulfur metabolism. Further genomic analysis of this strain revealed a mutation in the bi-functional alcohol/aldehyde dehydrogenase adhE gene, resulting in a strain with both NADH- and NADPH-dependent alcohol dehydrogenase activities, whereas the wild type strain can only utilize NADH. This is the exact same adhE mutation found in ethanol-tolerant C. thermocellum strain E50C, but ∆hydG∆ech is not more ethanol tolerant than the wild type. Targeting protein post-translational modification is a promising new approach to target multiple enzymes simultaneously for metabolic engineering. This GEO study pertains to expression profiles generated for C. thermocellum DSM 1313 strain adhE*(EA)