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Title: DEHALOGENATION OF THE HERBICIDES BROMOXYNIL (3,5-DIBROMO-4-HYDROXYBENZONITRILE) AND LOXYNIL (3,5-DIIODINO-4-HYDROXYBENZONITRILE) BY DESULFITOBACTERIUM CHLORORESPIRANS

Author
item Cupples, Alison
item SANFORD, ROBERT - UNIV OF ILLINOIS
item Sims, Gerald

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2005
Publication Date: 7/1/2005
Citation: Cupples, A.M., Sanford, R.A., Sims, G.K. 2005. Dehalogenation of the herbicides bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and ioxynil (3,5-diiodino-4-hydroxybenzonitrile) by desulfitobacterium chlororespirans. Applied and Environmental Microbiology. 71(7):3741-3746.

Interpretive Summary: The microorganism Desulfitobacterium chlororespirans was previously shown to obtain energy for growth by removing chlorine groups on chlorinated poly-substituted phenols. Here, we examined the ability of D. chlororespirans to transform the herbicides bromoxynil (3, 5-dibromo-4-hydroxybenzonitrile), and ioxynil (3, 5-diiodo-4-hydroxybenzonitrile), and the commonly reported bromoxynil soil degradation product (3, 5-dibromo-4-hydroxybenzoate, DBHB). We found that D. chlororespirans was able to remove the bromine groups from both bromoxynil and DBHB to form 4-cyanophenol and 4-hydroxybenzoate, respectively. Additionally, bromoxynil and DBHB were used as electron acceptors for growth. Doubling times (time for population of D. chlororespirans to double) for growth on bromoxynil (18.4 ± 5.2 hr) (mean ± standard deviation for triplicate cultures) and DBHB (11.9 ± 1.4 hr) were similar to those reported previously for growth in pyruvate (15 hr). In contrast, D. chlororespirans was unable to remove the iodine groups (deiodination) from ioxynil. However, when 3-chloro-4-hydroxybenzoate (a compound previously reported to support growth) was added, ioxynil was deiodinated to 4-cyanophenol. 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 indicates that dehalogenation can be an efficient removal process for halogenated herbicides under anaerobic conditions.

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.