Exogenous 5,6‐dimethylbenzimidazole caused production of a non‐functional tetrachloroethene reductive dehalogenase in S ulfurospirillum multivorans

Summary 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 G ram‐negative E psilonproteobacterium S ulfurospirillum 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 25 μ M , 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.