Bioremediation of organohalide pollutants: progress, microbial ecology, and emerging computational tools

Alleviating Chlorinated Alkane Inhibition on Dehalococcoides to Achieve Detoxification of Chlorinated Aliphatic Cocontaminants

“…Bioremediation employing Dehalococcoides populations capable of detoxifying chloroethenes has been widely applied to clean up relevant contamination sites. − Field bioremediation efforts and laboratory investigations have indicated that cocontamination with other chlorinated solvents significantly affects the effectiveness of bioremediation for chloroethenes. ,− Despite the recognition of this issue for a long time, a comprehensive evaluation of the toxicity of environmentally relevant chlorinated cocontaminants on the metabolic activity of Dehalococcoides and other associated syntrophic microorganisms is lacking. The present study ranked chloroform as the most detrimental cocontaminant inhibiting microbial reductive dechlorination of DCEs by Dehalococcoides -containing consortia, followed by 1,1,1-TCA and 1,1,2-TCA.…”

“…DCEs (0.25 mmol/L for each) with/without chlorinated cocontaminants at indicated concentrations were spiked to 20 mL serum bottles containing 4 mL of of a tris-HCl (100 mmol/L) buffered solution (pH 7.0) and titanium citrate (20 mmol/L). Methyl viologen (20 was spiked to the assay bottles with an estimated protein concentration of 2.5−3.8 mg/mL, which were stationarily incubated in the dark at 30 ± 1 °C. DCEs and their dechlorination products were monitored periodically to evaluate dechlorination activity of RDases in the crude cell extracts.…”

“…This capability is only credited to several members of Dehalococcoides and a single Dehalogenimonas strain. ,,− Nevertheless, these DCE-to-ethene dechlorinating OHRB provide unprecedented opportunities to employ OHRB to remediate sites polluted with chloroethenes. Notably, bioaugmentation using Dehalococcoides populations, particularly those capable of completely detoxifying chloroethenes, has become a mature technology to combat groundwater pollution of chlorinated solvents. − …”

Metabolic Synergy of Dehalococcoides Populations Leading to Greater Reductive Dechlorination of Polychlorinated Biphenyls

“…Bioaugmentation, which involves increasing the biomass of PCB-dechlorinating OHRB, has proven to be an effective strategy for enhancing the slow natural attenuation of PCBs. − In the past decade, successful bioremediation of PCBs in contaminated soils and sediments through bioaugmentation with the PCB-dechlorinating Dehalobium chlorocoercia strain DF-1 has been demonstrated. , However, strain DF-1 can dechlorinate only PCBs with double-flanked para -chlorines, and its capability to dechlorinate highly substituted PCB congeners found in Aroclor1260 and 1254 has not been reported. On the other hand, several Dehalococcoides mccartyi strains (e.g., CG1, CG4, CG5, and JNA) have demonstrated metabolic dechlorination of highly chlorinated commercial PCB mixtures, such as Aroclor1260 and 1254, , making them potential candidates for bioremediation.…”

Interspecies Mobility of Organohalide Respiration Gene Clusters Enables Genetic Bioaugmentation

“…Although the manufacture and use of many organohalides have been largely restricted due to their potential toxicity and tendency for bioaccumulation, the persistence of legacy pollution presents an ongoing challenge to impacted ecosystems and human populations. ,− After the discovery of microbial reductive dehalogenation in the 1980s, a group of researchers have contributed to a growing understanding of organohalide respiring bacteria (OHRB) and identified bacterial enrichments and isolates capable of dehalogenating diverse persistent organohalide pollutants. − Field-scale trials have demonstrated the environmental and economic benefits of in situ bioremediation for chlorinated solvents in contaminated groundwaters by bioaugmentation with an array of dehalogenating microbial populations. − However, the development of viable microbial consortia for remediation of organohalide pollutants has progressed slowly, with a limited number of platforms currently available for commercial application. Further, the efficacy of dehalogenating cultures used for in situ remediation could also be potentially hindered by inhospitable environmental conditions since some OHRB are notoriously fastidious and may struggle to gain a foothold among indigenous microbiota when subjected to suboptimal growth conditions (e.g., acidity, , presence of multiple dissimilar organohalide pollutants, and elevated concentrations of toxic organohalides) and resource competition with more metabolically versatile bacteria. , …”