CENSUS – Chlorinated Phenols

Detect and quantify bacteria responsible for biodegradation of Chlorinated Phenols

Pentachlorophenol (PCP) was one of the most widely used biocides in the US and despite residential use restrictions is still extensively used industrially as a wood preservative.  Along with PCP, the tetrachlorophenol and trichlorophenol isomers were also used as fungicides in wood preserving formulations.  2,4-dichlorophenol and 2,4,5-TCP were used as chemical intermediates in herbicide production (e.g. 2,4-D) and chlorophenols are known byproducts of chlorine bleaching in the pulp and paper industry.

Under aerobic conditions, PCP can be utilized as a sole source of carbon and energy by some bacteria.  PCP biodegradation is initiated by PCP 4-monooxygenase (PcpB) followed by two successive dehalogenation reactions (PcpC).  The intermediate produced is then cleaved by a dioxygenase (PcpA) and further metabolized (Cai and Xun 2002).

Under anaerobic conditions, PCP can serve as an electron acceptor for some Desulfitobacterium and Dehalococcoides species.  In each case however, complete reductive dechlorination of PCP to phenol was not observed.  Instead, PCP dechlorination by Dehalococcoides resulted in the production of a mixture of dichloro- and monochlorophenols.  Likewise, Desulfitobacterium strain PCP-1 dechlorinates PCP to 3-chlorophenol but other Desulfitobacterium species are only capable of ortho-dechlorination.  Thus the net production of lesser chlorinated phenol must be considered when evaluating reductive dechlorination as a mechanism for PCP biodegradation.

CENSUS Targets for Aerobic PCP

Target

MI Code

Relevance / Data Interpretation

Pentachlorophenol Monooxygenases qPCP CENSUS assay specifically targeting oxygenase genes encoding the enzymes responsible for initial oxidation of PCP and aromatic ring cleavage.

CENSUS Targets for Anaerobic PCP

Target

MI Code

 Relevance / Data Interpretation

Desulfitobacterium DSB Similar to Dehalococcoides, some species and strains of Desulfitobacterium are capable of utilizing PCP and other chlorinated phenols. Desulfitobacterium hafniense PCP-1 is capable of reductive dechlorination of PCP to 3-CP (Bourchard et al. 1996).  However the ability to biodegrade PCP is not universal amoung Desulfitobacterium isolates.  Desulfitobacterium sp. Strain PCE1 and D. chlororespirans strain Co23 for example can utilize TCP and DCP isomers but not PCP for growth (Gerritse et al.1996; Sandford et al. 1996).
Dehalococcoides DHC While the range of compounds utilized varies by strain, some Dehalococcoides isolates are capable of reductive dechlorination of PCP and other chlorinated phenols.  For example, Dehalococcoides strain CBDB1 is capable of utilizing PCP and all three tetrachlorophenol (TeCP) congeners, all six trichlorophenol (TCP) congeners, and 2,3-dichlorophenol (2,3-DCP).  PCP dechlorination by strain CBDB1 produces a mixture of 3,5-DCP, 3,4-DCP, 2,4-DCP, 3-CP and 4-CP (Adrian et al. 2007).   In the same study however, Dehalococcoides mccartyi  strain 195 dechlorinated a more narrow spectrum of chlorophenols which included 2,3-DCP, 2,3,4-TCP and 2,3,6-TCP but no other TCPs or PCP.

 

References

Adrian, L., S.K. Hansen, J.M. Fung, H. Gorisch, and S.H. Zinder. 2007. “Growth of Dehalococcoides strains with chlorophenols as electron acceptors”. Environmental Science & Technology. 41(7): 2318-2323.

Bouchard, B., R. Beaudet, R. Villemur, G. McSween, F. Lepine, and J.-G. Bisaillon. 1996. “Isolation and characterization of Desulfitobacterium frappieri sp. nov., an anerobic bacterium which reductively dechlorinates pentachlorophenol to 3-chlorophenol”. International Journal of Systematic Bacteriology. 46(4): 1010-1015.

Cai, M. and L. Xun. 2002. “Organization and regulation of pentachlorophenol-degrading genes in Spingobium chlorophenolicum ATCC 39723”. Journal of Bacteriology 184(17): 4672-4680.

Gerritse J, Renard V, Gomes TMP, Lawson PA, Collins MD, Gottschal JC. 1996. “Desulfitobacterium sp. strain PCE1, an anaerobic bacterium that can grow by reductive dechlorination of tetrachloroethene or ortho-chlorinated phenols”. Archives of Microbiology 165(2):132-140.

Padilla-Crespo, E, Yan, J, Swift, C, Wagner, DD, Chourey, K, Hettich, RL, Ritalahti, KM, Löffler, FE (2014) Identification and Environmental Distribution of dcpA, Which Encodes the Reductive Dehalogenase Catalyzing the Dichloroelimination of 1,2-Dichloropropane to Propene in Organohalide-Respiring Chloroflexi. Applied and Environmental Microbiology 80(3): 808-818.

Sanford RA, Cole JR, Loeffler FE, Tiedje JM. 1996. “Characterization of Desulfitobacterium chlororespirans sp. nov., which grows by coupling the oxidation of lactate to the reductive dechlorination of 3-chloro-4 hydroxybenzoate”. Applied and Environmental Microbiology 62(10):3800-3808.