The lower base of corrinoid small molecules regulates reductive dehalogenase enzyme function in Dehalococcoides species

Key interactions between proteins and small molecules regulate numerous environmental reactions. Such is the case with reductive dehalogenases that dechlorinate toxic chlorinated solvents only in the presence of corrinoid small molecules. Previous studies have demonstrated that the lower bases attached to these small molecule cofactors affect the activity of reductive dehalogenases differently in corrinoid auxotrophic Dehalococcoides mccartyi strains, which prefer the 5,6‐dimethylbenzimidazole (DMB) lower base. In contrast, Geobacter sulfurreducens strain PCA produces a small molecule corrinoid with 5‐hydroxybenzimidazole (5‐OHBza) as the lower base, which fails to support dechlorination catalyzed by reductive dehalogenases. Here, we cloned and heterologously expressed a unique Geobacter lovleyi O‐methyltransferase gene implicated in the methylation of 5‐OHBza to 5‐methoxybenzimidazole (5‐OMeBza). Unlike 5‐OHBza, 5‐OMeBza does support D. mccartyi reductive dechlorination activity. We demonstrated using HPLC and LC‐MS that the G. sulfurreducens mutant expressed the O‐methyltransferase, as evidenced by the native 5‐OHBza‐cobamide being converted into the 5‐OMeBza‐cobamide. Next, we co‐cultured D. mccartyi and the recombinant G. sulfurreducens in the absence of exogenous vitamin B 12 , which supported D. mccartyi growth and the complete dechlorination of cis ‐1,2‐dichloroethene to ethene. These studies demonstrated that the O‐methyltransferase catalyzes a critical step in lower base biosynthesis and provides a genetic basis for the observation that D. mccartyi reductive dechlorination activity occurs in co‐cultures with G. lovleyi but not with G. sulfurreducens . Our results emphasize the critical role of small molecule interactions directing protein function in the case of dechlorinating toxic chlorinated solvents. Support or Funding Information The authors acknowledge funding support from the NIH and SERDP. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .