Evidence for a Putative Isoprene Reductase in Acetobacterium wieringae

Area of Science:

• Microbial metabolism and genomics
• Biogeochemical cycling
• Enzyme function and evolution

Background:

• Isoprene-metabolizing microorganisms are increasingly recognized for their role in the global isoprene budget.
• Under anoxic conditions, isoprene can function as an electron acceptor, being reduced to methylbutene.
• The molecular mechanisms underlying isoprene reduction by bacteria remain largely uncharacterized.

Purpose of the Study:

• To identify the specific organisms and genes responsible for isoprene hydrogenation in anoxic environments.
• To elucidate the molecular basis of isoprene reduction by employing proteogenomic profiling.
• To investigate the evolutionary distribution of genes involved in unsaturated hydrocarbon biohydrogenation.

Main Methods:

• Proteogenomic profiling of an isoprene-reducing bacterial enrichment culture.
• Metagenome-assembled genome (MAG) reconstruction, focusing on the dominant Acetobacterium wieringae lineage.
• Comparative genomics and reverse transcription-PCR (RT-PCR) to identify upregulated genes during isoprene reduction.

Main Results:

• A metagenome-assembled genome of Acetobacterium wieringae (89% relative abundance) was obtained.
• A putative five-gene operon, including an oxidoreductase and nickel chaperones, was identified and found to be upregulated during isoprene reduction.
• Homologs of the putative isoprene reductase were found across diverse bacterial phyla, suggesting broader biohydrogenation capabilities.

Conclusions:

• The identified five-gene operon in Acetobacterium wieringae is proposed to be responsible for isoprene reduction.
• The putative isoprene reductase possesses conserved domains for cofactor binding and iron-sulfur clusters.
• The widespread distribution of reductase homologs suggests that biohydrogenation of unsaturated hydrocarbons is a more common microbial process than previously thought.