The soluble di-iron monooxygenases (SDIMOs) are of special interest due to their broad substrate range, high enantioselectivity, and ability to oxidise very inert substrates (e.g. methane). A novel SDIMO harboured by the soil bacterium Solimonas soli DCY-12 (ZmoABCD) was partially characterised. S. soli is unable to grow with alkenes as a source of carbon and energy, but expression of the zmoABCD genes in Pseudomonas putida KT2440 allowed epoxidation of C2-C8 alkenes, with a preference for small linear alkenes especially propene. The organochlorine pollutants vinyl chloride and cis-1,2-dichloroethene were also oxidized by ZmoABCD, as such the enzyme may have potential for use in the biodegradation of these common groundwater pollutants.
Regulation of zmo expression was studied by replacing the zmoABCD cluster in the genome of S. soli with a gfp reporter gene, in order to identify potential zmo-inducing substrates. The same construct was used to study expression of the zmo promoter in E. coli, with particular focus on the 120 bp untranslated region upstream of the SDIMO cluster. The distal 60 bp of this untranslated region has an exceptionally high GC content (80 %) and is predicted to form large GC-rich hairpins, suggesting that it may play a regulatory role in zmo expression. In E. coli, deletion of the entire 120-bp region in a multicopy plasmid carrying the gfp reporter led to a 6-fold increase in GFP fluorescence. Partial deletions of the region gave similar results and allowed the effect to be localised. It is hypothesized that an operator region exists in this region, and experiments are in progress to elucidate its mode of action. Through understanding the regulation of ZmoABCD, we will further our knowledge of SDIMO regulation, as well as unlocking the potential for ZmoABCD to be employed in the biodegradation of chlorinated alkenes.