Kinetics of the Microbial Reductive Dechlorination of Pentachloroaniline

Abstract

The microbial reductive dechlorination kinetics of pentachloroaniline (PCA) and less chlorinated anilines (CAs) were investigated with a mixed, fermentative/ methanogenic culture. Batch dechlorination assays were performed with all available CAs at an initial concentration of 3 microM, and an incubation temperature of 22 degrees C. Dechlorination of PCA, two tetrachloroanilines (2,3,4,5- and 2,3,5,6-TeCA), five trichloroanilines (2,3,4-, 2,3,5-, 2,4,5-, 2,4,6-, and 3,4,5-TrCA), and one dichloroaniline (3,5-DCA; low extent) was observed but none of the five remaining dichloroanilines and three monochloroanilines were dechlorinated by the enrichment culture during batch assays. The dechlorination rates (k') and half-saturation coefficients (Kc) were measured using nonlinear regression based on the integrated Michaelis-Menten equation under conditions of electron donor saturation and assuming constant biomass concentration over the relatively short batch incubation period. At an initial concentration of CAs of about 3 microM, the values of k' and Kc ranged from 0.25 to 1.19 microM/day and from 0.11 to 1.72 microM, respectively, corresponding to half-lives in the range of 1.5-8.5 days. Model simulations of the sequential dechlorination reactions based on a branched-chain Michaelis-Menten model and using independently measured k' and Kc values matched the experimental data very well.

Microbial transformation of pentachloronitrobenzene under nitrate reducing conditions

“…It is noteworthy that a mixed, methanogenic and PCA-dechlorinating culture was successfully developed within 35 days of incubation using as inoculum the same sediment which was also used in the present study for the development of the denitrifying cultures (Okutman Tas and Pavlostathis 2005). The presence of halorespiring bacteria in the mixed, methanogenic and PCA-dechlorinating culture, such as Dehalococcoides, was confirmed based on 16S rRNA gene analysis using a nested PCR approach (Okutman Tas et al 2006). Therefore, long-term, active nitrate reducing conditions maintained in the PCNB-acclimated culture in the present study prevented the development of halorespiring, PCA-dechlorinating bacteria.…”

“…The U.S. EPA has classified PCNB as a possible cancer causing substance, has included it in the Toxicity Class III chemicals list, as well as in the list of 'Waste Minimization Priority Chemicals' (U.S. EPA 2003). Pentachloroaniline (PCA) is the main abiotic and first biotic transformation product of PCNB under anoxic/ anaerobic conditions (Hakala et al 2007;Klupinski et al 2004;Okutman Tas and Pavlostathis 2005, 2008Okutman Tas et al 2006;Susarla et al 1996;Tamura et al 1995). PCA has a lower aqueous solubility, a higher tendency to partition into natural organic matter compared to PCNB (Okutman Tas and Pavlostathis 2005), and a higher bioconcentration factor (1000) compared to that of PCNB (750) (U.S. EPA 2003).…”

“…The biotransformation potential and kinetics of PCNB under methanogenic conditions is well documented (Kuhn and Suflita 1989;Okutman Tas and Pavlostathis 2005;Okutman Tas et al 2006;Susarla et al 1997). Aside from carbonate (methanogenesis), a wide variety of alternative electron acceptors can also be used by microorganisms under anoxic/anaerobic conditions.…”

Anaerobic Dehalogenation of Chloroanilines by Dehalococcoides mccartyi Strain CBDB1 and Dehalobacter Strain 14DCB1 via Different Pathways as Related to Molecular Electronic Structure

“…Whereas in oxic environments, lower chlorinated anilines can be transformed to chlorocatechols and subsequently used as carbon and nitrogen source by a variety of microorganisms, , little is known about their transformation in anoxic environments. Anaerobic transformation was observed in methanogenic aquifers and aquifer slurries, ,− flooded soils, and estuarine sediments; the responsible organisms, however, were not identified. In mixed consortia, different dehalogenation pathways were observed: in anaerobic enrichment cultures with estuarine sediments as an inoculum, pentachloroaniline (PeCA) was converted to 2,3,4,5-tetrachloroaniline (2,3,4,5-TeCA), i.e., via ortho -dechlorination.…”

Temperature and pH Effect on the Microbial Reductive Transformation of Pentachloronitrobenzene

“…Complete reduction of the nitro group is the first step in the reductive transformation of PCNB, resulting in the formation of pentachloroaniline (PCA) ( − ). Microbial reductive transformation of PCA resulted in its sequential dechlorination down to di- and in some cases monochloroanilines, but the resulting monochloroanilines were not transformed further ( − ).…”