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.
