Dehalogenation of the Herbicides Bromoxynil (3,5-Dibromo-4-Hydroxybenzonitrile) and Ioxynil (3,5-Diiodino-4-Hydroxybenzonitrile) by Desulfitobacterium chlororespirans

Abstract

Desulfitobacterium chlororespirans has been shown to grow by coupling the oxidation of lactate to the metabolic reductive dehalogenation 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 to 4-cyanophenol and DBHB to 4-hydroxybenzoate occurred. Further, bromoxynil (35 to 75 M) and DBHB (250 to 260 M) were used as electron acceptors for growth. Doubling times for growth (means ؎ standard deviations for triplicate cultures) on bromoxynil (18.4 ؎ 5.2 h) and DBHB (11.9 ؎ 1.4 h), determined by rate of [ 14 C]lactate uptake into biomass, were similar to those previously reported for this microorganism during growth on pyruvate (15.4 h). 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 Desulfitobacterium 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.An increasingly popular approach for the remediation of halogenated environmental pollutants is biological reductive dehalogenation. Dechlorination is the most commonly reported reductive dehalogenation process, due to the widespread pollution of chlorinated compounds (e.g., tetrachloroethene, trichloroethene, or chlorinated phenols), with few reports on the reduction of other halogens. However, the expanding list of emerging halogenated contaminants, including polybrominated fire retardants (20), disinfection by-products (32), perfluorinated surfactants (5), and pesticides (9, 26), illustrates the need for a greater understanding of defluorination, debromination, and deiodination. To address this, the unexploited potential of previously isolated chlororespiring microorganisms is of particular interest.Bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) is used for the postemergence control of annual broad-leaved weeds in cereals, maize, sorghum, flax, allium species, mint, and grass seed crops (35) (Fig. 1). The octanoate ester of bromoxynil (3,5-dibromo-4-cyanophenyl octanoate), also an herbicide, is readily degraded in nonsterile water and in other biological systems to bromoxynil (35). Ioxynil (3,5-diiodo-4-hydroxybenzonitrile) (Fig. 1) is used for the postemergence control of annual broad-leaved weeds in cereals, onions, leeks, shallots, flax, sugar cane, forage grasses, lawns, and turf (35).

Effect of buctril super (Bromoxynil) herbicide on soil microbial biomass and bacterial population

“…Elevated clay contents lengthened the persistence of herbicide in the soil and prolonged time of exposure of the herbicide to soil bacteria, resulting decline in their population. Cupples et al (2005) also observed prolonged persistence of herbicide due to high clay contents in the soil. This drop in bacterial population might be because of rapid mortality of bacteria due to herbicide.…”

Biostimulation for the Enhanced Degradation of Herbicides in Soil

“…Examples of herbicides that have been shown to be subject to reductive dechlorination include alachlor, metolachlor, and propachlor [78]. Both the bromine and iodine atoms have also been shown to be removed from certain herbicides (e.g., bromoxynil and ioxynil) by known chlorine respiring bacteria, such as Desulfitobacterium chlororespirans [79].…”

Characterization of a Highly Enriched Microbial Consortium Reductively Dechlorinating 2,3-Dichlorophenol and 2,4,6-Trichlorophenol and the Corresponding cprA Genes from River Sediment

“…Desulfitobacterium spp. have been cited in many studies as dechlorinating bacteria (Bouchard et al, 1996;Breitenstein et al, 2001;Cupples et al, 2005;Villemur et al, 2006). Highly enriched cultures showed the prevalence of curved rods, a characteristic feature of Desulfitobacterium spp.…”

“…Desulfitobacterium dehalogenans strain JW/IU-DC1, first documented by Utkin et al (1994), was reported for its dechlorination of 2,3DCP, 2,6DCP, and 2,4,6TCP . Subsequently, other strains belonging to the genus Desulfitobacterium with dechlorination activity toward CPs were isolated and characterized, these included Desulfitobacterium chlororespirans strain Co23 Cupples et al, 2005), Desulfitobacterium hafniense strain DCB-2 (Christiansen and Ahring, 1996), strain TCP-A (Breiten stein et al, 2001), and strain PCP-1 (Bouchard et al, 1996;Villemur, 2013). The obligate anaerobic bacterium Dehalococcoides ethenogenes strain 195 known for its ability to dechlorinate tetrachloroethene (Maymo-Gatell et al, 1997) was recently reported to possess diverse dehalogenation ability.…”