Polychlorobiphényle

Les polychlorobiphényles (PCB), aussi appelés biphényles polychlorés (BPC), ou encore parfois improprement dits « pyralènes » (du nom commercial d'un produit de Monsanto à base de PCB autrefois très utilisé en Europe dans les transformateurs) forment une famille de organochlorés dérivés du biphényle. Ils sont industriellement synthétisés, et chimiquement proches des polychloroterphényles, polychlorodibenzo-furanes et des dioxines. Ce sont (selon leur teneur en chlore) des liquides plus ou moins visqueux, voire résineux, insolubles dans l'eau, incolores ou jaunâtres, à forte odeur aromatique. Très stables à la chaleur, ils ne se décomposent qu'à des températures dépassant . Leur inertie chimique les rend peu sensibles aux acides, bases et oxydants. Ils peuvent dissoudre ou ramollir certains caoutchoucs et matières plastiques. Les PCB sont toxiques, écotoxiques et reprotoxiques (y compris à faible dose en tant que perturbateurs endocriniens). Ce sont des polluants ubiquitaires et p

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vignette|En 1958, le programme national d'éradication du paludisme des États-Unis a utilisé une approche entièrement nouvelle mettant en œuvre le DDT pour la pulvérisation des moustiques. Le DDT, déve

vignette|Les détritus de type déchets ménagers sont souvent indicateurs de pollutions (métaux lourds, micro-organismes) posant des problèmes de santé publique, notamment dans les régions où les eaux d

vignette|Le siège de l'EPA à Washington. L'Agence de protection de l’environnement des États-Unis (United States Environmental Protection Agency ou EPA) est une agence indépendante du gouvernement de

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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

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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

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Competition of two Sulfurospirillum populations for tetrachloroethene

Géraldine Florence Buttet

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

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ENV-200: Environmental chemistry

This course provides students with an overview over the basics of environmental chemistry. This includes the chemistry of natural systems, as well as the fate of anthropogenic chemicals in natural systems. It enables students to apply general chemical concepts to natural systems.