Complete Reductive Dehalogenation of Brominated Biphenyls by Anaerobic Microorganisms in Sediment

Abstract

We sought to determine whether microorganisms from the polychlorinated biphenyl (PCB)-contaminated sediment in Woods Pond (Lenox, Mass.) could dehalogenate brominated biphenyls. The PCB dechlorination specificities for the microorganisms in this sediment have been well characterized. This allowed us to compare the dehalogenation specificities for brominated biphenyls and chlorinated biphenyls within a single sediment. Anaerobic sediment microcosms were incubated separately at 25°C with 16 different mono- to tetrabrominated biphenyls (350 μM) and disodium malate (10 mM). Samples were extracted and analyzed by gas chromatography with an electron capture detector and a mass spectrometer detector at various times for up to 54 weeks. All of the tested brominated biphenyls were dehalogenated. For most congeners, including 2,6-dibromobiphenyl (26-BB) and 24-25-BB, the dehalogenation began within 1 to 2 weeks. However, for 246-BB and 2-2-BB, debromination was first observed at 7 and 14 weeks, respectively. Most intermediate products did not persist, but when 2-2-BB was produced as a dehalogenation product, it persisted for at least 15 weeks before it was dehalogenated to 2-BB and then to biphenyl. The dehalogenation specificities for brominated and chlorinated biphenyls were similar: meta andpara substituents were generally removed first, andortho substituents were more recalcitrant. However, the brominated biphenyls were better dehalogenation substrates than the chlorinated biphenyls. All of the tested bromobiphenyls, including those with ortho and unflankedmeta and para substituents, were ultimately dehalogenated to biphenyl, whereas their chlorinated counterparts either were not dehalogenation substrates or were only partially dehalogenated. Our data suggest that PCB-dechlorinating microorganisms may be able to dehalogenate brominated biphenyls and may exhibit a relaxed specificity for these substrates.

Brominated Biphenyls Prime Extensive Microbial Reductive Dehalogenation of Aroclor 1260 in Housatonic River Sediment

“…Based on their findings, these authors proposed that PCB-dechlorinating microorganisms might be able to dehalogenate brominated biphenyls. Likewise, we recently found that the anaerobic microorganisms in Woods Pond sediment can dehalogenate many mono-, di-, and tribrominated biphenyls even though the upper Housatonic River has no history of contamination with brominated biphenyls (6). Our data suggested that PCB-dehalogenating microorganisms in Woods Pond might exhibit relaxed specificity for brominated biphenyl dehalogenation.…”

“…Therefore, when referring to halogenated biphenyls, we use the term micromolar (M) to mean micromoles per liter of slurry. In most cases, disodium malate was also added to a final concentration of 10 mM because previous experiments showed that malate accelerated dehalogenation (6). No other nutrients were added.…”

“…Dehalogenation of the brominated biphenyls was monitored by GC with a mass spectrometer operated in the selected ion mode as previously described (6). Debromination products were identified as described previously (6). PCB dechlorination was monitored by high-resolution capillary GC analysis with a Ni 63 electron capture detector (ECD).…”

Novel reductive dehalogenases from the marine sponge associated bacterium Desulfoluna spongiiphila

“…Many brominated pollutants, such as brominated biphenyls and tetrabromobisphenol A are ubiquitously present in the environment and reductive dehalogenation is considered crucial in their biodegradation (e.g., Bedard and Van Dort, 1998;Voordeckers et al, 2002;Liu et al, 2013). Reductive debromination has been observed in sediment microcosms (e.g., Monserrate and H€ aggblom, 1997), and some bacteria are reported with reductive debromination ability, for example, a highly enriched Dehalococcoides culture was able to debrominate polybrominated diphenyl ethers, tetrabromobisphenol A and other phenolic bromoaromatics (He et al, 2006;Lee et al, 2011;Cooper et al, 2015;Yang et al, 2015), and Desulfovibrio strains and Desulfobacterium chlororespirans are reported to debrominate brominated phenolics (Boyle et al, 1999;Fennell et al, 2004;Cupples et al, 2005).…”

Reductive dehalogenation of brominated ethenes by Sulfurospirillum multivorans and Desulfitobacterium hafniense PCE‐S

“…In the studies available on the microbial dehalogenation of brominated compounds, bromine substituents seem to be easier removable than chlorine substituents (Wu and Wiegel, 1997;Bedard and Van Dort, 1998;Boyle et al, 1999;Voordeckers et al, 2002). This may be partially due to the more labile nature of the carbon-bromine bond (Vogel et al, 1987;Allard and Neilson, 2003); also, debromination is thermodynamically more favourable than dechlorination (Dolfing, 2003).…”