Isobutylene (2-methylpropene IB) is the simplest branched alkene and is used industrially to produce a wide range of products, ranging from fuel oxygenates to automobile tires. Only members of the Mycobacteriaceae family, including Mycolicibacterium sp. ELW1, are known to aerobically catabolize IB as a sole carbon and energy source. A multi-omics approach established two gene clusters on a large catabolic plasmid, pELW1-1, carried by Mycolicibacterium sp. ELW1. These two clusters separately contain the predicted genes necessary for the catabolism of IB to 2-hydroxyisobutyrate (2-HIBA) (cluster 1) and the biosynthesis of cobalamin and the further cobalamin-dependent transformation of 2-HIBA to acetyl-CoA (cluster 2). Curing strain ELW1 of pELW1-1 resulted in the loss of the ability of ELW1 to grow on IB and downstream metabolites, including isobutylene oxide (IBO), 2-methyl-1,2-propanediol (MPD), and 2-hydroxyisobutyrate (2-HIBA). Transcriptomic and proteomic analyses, combined with activity-based labeling, growth, and whole-cell activity assays, confirmed that the plasmid-borne ibc genes are strongly induced during growth on IB and that the plasmid is obligatory for IB catabolism.IMPORTANCEMycolicibacterium sp. ELW1 is one of three strains isolated from across the world that are known to catabolize and grow aerobically on isobutylene (IB), the shortest branched alkene. IB catabolism is initiated by a monooxygenase and proceeds through a pathway that intersects with the methyl tertiary-butyl ether (MTBE) biodegradation pathway. The plasmid localization, gene organization, and gene induction pattern shown here provide insights into the role of large catabolic plasmids in the aerobic catabolism of gaseous alkenes.
Joyce et al. (Fri,) studied this question.