Polychlorinated biphenyl

Summary

Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1976 and internationally by the Stockholm Convention on Persistent Organic Pollutants in 2001. PCBs are organic chlorine compounds with the formula C12H10−xClx; they were once widely used in the manufacture of carbonless copy paper, as heat transfer fluids, and as dielectric and coolant fluids for electrical equipment. Because of their longevity, PCBs are still widely in use, even though their manufacture has declined drastically since the 1960s, when a host of problems were identified. With the discovery of PCBs' environmental toxicity, and classification as persistent organic pollutants, their production was banned by United States federal law on January 1, 1978, under Title 15 U.S.Code 2605(e) Polychlorinated biphenyls, in subsection (2)(A) established that after J

Official source

https://en.wikipedia.org/wiki/Polychlorinated_biphenyl

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Coexistence of two distinct Sulfurospirillum populations respiring tetrachloroethene-genomic and kinetic considerations

Mélissa Burion, Géraldine Florence Buttet, Christof Holliger, Alexandra Marie Murray

Two anaerobic bacterial consortia, each harboring a distinct Sulfurospirillum population, were derived from a 10 year old consortium, SL2, previously characterized for the stepwise dechlorination of tetrachloroethene (PCE) to cis-dichloroethene (cis-DCE) via accumulation of trichloroethene (TCE). Population SL2-1 dechlorinated PCE to TCE exclusively, while SL2-2 produced cis-DCE from PCE without substantial TCE accumulation. The reasons explaining the long-term coexistence of the populations were investigated. Genome sequencing revealed a novel Sulfurospirillum species, designated 'Candidatus Sulfurospirillum diekertiae', whose genome differed significantly from other Sulfurospirillum spp. (78%-83% ANI). Genome-wise, SL2-1 and SL2-2 populations are almost identical, but differences in their tetrachloroethene reductive dehalogenase sequences explain the distinct dechlorination patterns. An extended series of batch cultures were performed at PCE concentrations of 2-200 μM. A model was developed to determine their dechlorination kinetic parameters. The affinity constant and maximal growth rate differ between the populations: the affinity is 6- to 8-fold higher and the growth rate 5-fold lower for SL2-1 than SL2-2. Mixed cultivation of the enriched populations at 6 and 30 μM PCE showed that a low PCE concentration could be the driving force for both functional diversity of reductive dehalogenases and niche specialization of organohalide-respiring bacteria with overlapping substrate ranges.

2018

Coexistence of two distinct Sulfurospirillum populations respiring tetrachloroethene—genomic and kinetic considerations

Mélissa Burion, Géraldine Florence Buttet, Christof Holliger, Julien Maillard, Alexandra Marie Murray

Two anaerobic bacterial consortia, each harboring a distinct Sulfurospirillum population, were derived from a 10 year old consortium, SL2, previously characterized for the stepwise dechlorination of tetrachloroethene (PCE) to cis-dichloroethene (cis-DCE) via accumulation of trichloroethene (TCE). Population SL2-1 dechlorinated PCE to TCE exclusively, while SL2-2 produced cis-DCE from PCE without substantial TCE accumulation. The reasons explaining the long-term coexistence of the populations were investigated. Genome sequencing revealed a novel Sulfurospirillum species, designated ‘Candidatus Sulfurospirillum diekertiae’, whose genome differed significantly from other Sulfurospirillum spp. (78%–83% ANI). Genome-wise, SL2-1 and SL2-2 populations are almost identical, but differences in their tetrachloroethene reductive dehalogenase sequences explain the distinct dechlorination patterns. An extended series of batch cultures were performed at PCE concentrations of 2–200 μM. A model was developed to determine their dechlorination kinetic parameters. The affinity constant and maximal growth rate differ between the populations: the affinity is 6- to 8-fold higher and the growth rate 5-fold lower for SL2-1 than SL2-2. Mixed cultivation of the enriched populations at 6 and 30 μM PCE showed that a low PCE concentration could be the driving force for both functional diversity of reductive dehalogenases and niche specialization of organohalide-respiring bacteria with overlapping substrate ranges.

FEMS Microbiology Ecology, Vol. 94, Issue 12018

Tetrachloroethene (PCE) represents a major groundwater pollutant. Some bacteria are able to use PCE as electron acceptor in an anaerobic respiration process called organohalide respiration (OHR). An anaerobic enrichment culture (named SL2-PCEb) consisting of two different Sulfurospirillum populations was obtained from a fixed-bed bioreactor sludge treating PCE-contaminated groundwater (1). The peculiarity of this bacterial consortium resides in stepwise dechlorination of PCE to trichloroethene (TCE) and cis-dichloroethene (cis-DCE), which is catalyzed by the two populations successively (2). Two subcultures were derived from SL2-PCEb, each one harboring one Sulfurospirillum population and showing distinct dechlorination potential: SL2-PCEc dechlorinates PCE to TCE only, while SL2-TCE (selected on TCE) kept the potential to dechlorinate both PCE and TCE. A molecular fingerprinting method targeting small differences in their rdhA genes was developed to follow the dynamics of both populations. The dechlorination activity of both populations suggested that the RdhA enzyme produced by SL2-PCEc has a higher turnover rate than the one produced by SL2-TCE (3). The present work proposes to study the competition of both SL2-PCEc and SL2-TCE populations for PCE by mixing them with different proportions and following their growth and activity. To this purpose, a new experimental set-up was developed by combining quantitative PCR and fragment analysis. This should highlight the physiological and molecular basis of the two RdhA enzymes for substrate affinity and enzymatic activity.

2016