Technical Abstract: Desulfitobacterium chlororespirans has been shown to grow by coupling the oxidation of lactate to the reductive dechlorination of ortho-chlorines on polysubstituted phenols. Here, we examine the ability of D. chlororespirans to debrominate and deiodinate the polysubstituted herbicides bromoxynil (3, 5-dibromo-4-hydroxybenzonitrile), ioxynil (3, 5-diiodo-4-hydroxybenzonitrile), and the bromoxynil metabolite 3, 5-dibromo-4-hydroxybenzoate (DBHB). Stoichiometric debromination of bromoxynil and DBHB to 4-cyanophenol and 4-hydroxybenzoate, respectively, occurred. Further, bromoxynil and DBHB were used as electron acceptors for growth. Doubling times for growth on bromoxynil (18.4 ± 5.2 hr) (mean ± standard deviation for triplicate cultures) and DBHB (11.9 ± 1.4 hr), determined by rate of [14C] lactate uptake into biomass, were similar to those previously reported for this microorganism during growth on pyruvate (15.4 hr). In contrast, ioxynil was not deiodinated when added alone or when added with bromoxynil, however, ioxynil dehalogenation, with stoichiometric conversion to 4-cyanophenol, was observed when the culture was amended with 3-chloro-4-hydroxybenzoate (a previously reported electron acceptor). To our knowledge, this is the first direct report of deiodination by a bacterium in the Desulfitobacteria genus and the first report of an anaerobic pure culture with the ability to transform bromoxynil or ioxynil. This research provides valuable insights into the substrate range of D. chlororespirans.