Exogenous 5,6-dimethylbenzimidazole caused production of a non-functional tetrachloroethene reductive dehalogenase in Sulfurospirillum multivorans

Corrinoid-dependent reductive dehalogenation is mediated by phylogenetically diverse anaerobic bacteria that either synthesize corrinoids de novo or are dependent on corrinoid salvaging from the environment. The tetrachloroethene (PCE) reductive dehalogenase (PceA) of the Gram-negative Epsilonproteobacterium Sulfurospirillum multivorans harbours a norpseudo-B-12 as corrinoid cofactor. Norpseudo-B-12 differs from coenzyme B-12 in the nucleotide loop structure. Adenine instead of 5,6-dimethylbenzimidazole (DMB) serves as lower ligand base of the central cobalt ion, and the nucleotide loop of norpseudo-B-12 lacks a methyl group at position 176. In this study, S.multivorans was grown anaerobically with PCE in the presence of DMB. At a DMB concentration of 25M, the adenine moiety in the nucleotide loop of norpseudo-B-12 was quantitatively replaced by DMB. The formation of the DMB-containing nor-B-12 severely affected PCE-dependent growth and the PceA activity. In DMB-treated cells processing of the cytoplasmic PceA precursor was impeded, a result pointing to retarded cofactor incorporation. PceA enriched from cells cultivated with DMB contained nor-B-12. Nor-B-12 purified from cells grown in the presence of DMB mediated the abiotic reductive dehalogenation of trichloroacetate to dichloroacetate at a 25-fold lower rate in comparison with norpseudo-B-12, a fact underpinning the relevance of norpseudo-B-12 as efficient catalyst for reductive dehalogenation in general.