CENSUS – Chlorinated Propanes
|Detect and quantify bacteria responsible for biodegradation of chlorinated propanes
Chlorinated propanes were used as industrial solvents, extractants, degreasers, and as intermediates in the synthesis of other chlorinated chemicals. 1,2-dichloropropane (DCP) was once commonly used as a soil fumigant for root-parasitic nematodes and insecticide for stored grain. 1,2,3-trichloropropane (TCP) is formed as a by-product during synthesis of a number of chemicals and was historically present in commercial soil fumigants.
Under anaerobic conditions, Dehalogenimonas spp. and some Dehalococcoides strains are capable of utilizing chlorinated propanes as growth supporting electron acceptors. Dehalogenimonas isolates characterized to date appear to specialize in the dichlorelimination of a variety of chlorinated alkanes including TCP and DCP. Reductive dechlorination of TCP by Dehalogenominas produces an unstable intermediate (allyl chloride) which can by hydrolyzed to form allyl alcohol or undergo reactions with sulfide-reducing agents for form allyl sulfides (Yan et al. 2009). In Dehalococcoides strains and Dehalogenimonas spp., DCP undergoes dichloroelimination mediated by a dichloropropane dehalogenase to form propene (Ritalahti and Löffler 2004).
CENSUS Targets for Chlorinated Propanes
Although 1,3-dichloropropane (1,3-DCP) can serve as a growth supporting carbon and energy source under aerobic conditions, attempts to enrich and isolate aerobic 1,2,3-trichloropropane (TCP) utilizing bacteria have been unsuccessful to date. Similarly, only one study has reported aerobic metabolism of 1,2-DCP (based on loss of the compound). Known haloalkane dehalogenase enzymes have shown little activity against chlorinated propanes (Samin and Janssen 2012).
However, chlorinated propanes can be susceptible to aerobic cometabolism. More specifically, methanotrophs expressing soluble methane monooxygenase (sMMO) are capable of co-oxidizing 1,2-DCP, 1,3-DCP and 1,2,3-TCP (Bosma and Janssen 1998; Oldenhuis et al. 1989). Cometabolism of 1,2,3-TCP has been also demonstrated for propane oxidizing bacteria (Wang and Chu 2017).
TCP cometabolism has also been observed for mixed cultures of aromatic hydrocarbon degraders (Leahy et al. 2003). Since the experiment was performed as a mixed culture, TCE cometabolism could not be explicitly linked to individual aromatic oxygenase genes. However, the broad specificity of aromatic monooxygenases is well known and the mixture cultures in the Leahy et al. (2003) included strains utilizing toluene monooxygenase (RMO, RDEG), phenol hydroxylase (PHE) and toluene dioxygenase (TOD) pathways. Moreover, there is increasing evidence that aromatic oxygenases play a role in cometabolism of chlorinated hydrocarbons even in the absence of the primary substrate (ESTCP ER-201584).
Bosma, T., and D.B. Janssen. 1998. Conversion of chlorinated propanes by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied Microbiology and Biotechnology 50 no. 1: 105-112.
Leahy, J.G., K.D. Tracy, and M.H. Eley. 2003. Degradation of volatile hydrocarbons from steam-classified solid waste by a mixture of aromatic hydrocarbon-degrading bacteria. Biotechnology Letters 25 no. 6: 479-483.
Oldenhuis, R., R.L. Vink, D.B. Janssen, and B. Witholt. 1989. Degradation of chlorinated aliphatic hydrocarbons by Methylosinus trichosporium OB3b expressing soluble methane monooxygenase. Applied and Environmental Microbiology 55 no. 11: 2819-2826.
Ritalahti, K.M., and F.E. Löffler. 2004. Populations Implicated in Anaerobic Reductive Dechlorination of 1,2-Dichloropropane in Highly Enriched Bacterial Communities. Applied and Environmental Microbiology 70 no. 7: 4088-4095.
Samin, G., and D.B. Janssen. 2012. Transformation and biodegradation of 1,2,3-trichloropropane (TCP). Environmental Science and Pollution Research International 19 no. 8: 3067-3078.
Wang, B., and K.-H. Chu. 2017. Cometabolic biodegradation of 1,2,3-trichloropropane by propane-oxidizing bacteria. Chemosphere 168: 1494-1497.
Yan, J., B.A. Rash, F.A. Rainey, and W.M. Moe. 2009. Isolation of novel bacteria within the Chloroflexi capable of reductive dechlorination of 1,2,3-trichloropropane. Environmental Microbiology 11 no. 4: 833-843.