Microbiological aspects of the removal of chlorinated hydrocarbons from air

Chlorinated hydrocarbons are widely used synthetic chemicals that are frequently present in industrial emissions. Bacterial degradation has been demonstrated for several components of this class of compounds. Structural features that affect the degradability include the number of chlorine atoms and the presence of oxygen substituents. Biological removal from waste streams of compounds that serve as a growth substrate can relatively easily be achieved. Substrates with more chlorine substituents can be converted cometabolically by oxidative routes. The microbiological principles that influence the biodegradability of chlorinated hydrocarbons are described. A number of factors that will determine the performance of microorganisms in systems for waste gas treatment is discussed. Pilot plant evaluations, including economics, of a biological trickling filter for the treatment of dichloromethane containing waste gas indicate that at least for this compound biological treatment is cost effective.

Degradation of 2-Chloroethylvinylether by Ancylobacter aquaticus AD25 and AD27

Incubation of five different 1-chloroethers with slurries prepared from brackish water sediment or activated sludge revealed that bis(2-chloroethyl)ether and 2-chloroethylvinylether (2-CVE) were biodegradable under aerobic conditions. After enrichment, two different cultures of Ancylobacter aquaticus that are capable of growth on 2-CVE were isolated. Both cultures were also able to grow on 1,2-dichloroethane. The cells contained a haloalkane dehalogenase that dehalogenated 2-CVE, 2-chloroethylmethylether, 2-bromoethylethylether, and epichlorohydrin. Experiments with cell extracts indicated that an alcohol dehydrogenase and an aldehyde dehydrogenase were also involved in the degradation of 2-CVE. This suggests that 2-CVE is metabolized via 2-hydroxyethylvinylether and vinyloxyacetaldehyde to vinyloxyacetic acid. Enzymatic ether cleavage was not detected. 2-CVE was also degraded by chemical ether cleavage, leading to the formation of 2-chloroethanol and acetaldehyde, both of which supported growth. We propose that A. aquaticus strains may be important for the detoxification and degradation of halogenated aliphatic compounds in the environment.

Characterization of the epoxide hydrolase from an epichlorohydrin-degrading Pseudomonas sp.

An epoxide hydrolase was purified to homogeneity from the epichlorohydrin-utilizing bacterium Pseudomonas sp. strain AD1. The enzyme was found to be a monomeric protein with a molecular mass of 35 kDa. With epichlorohydrin as the substrate, the enzyme followed Michaelis-Menten kinetics with a Km value of 0.3 mM and a Vmax of 34 µmol · min-1 · mg protein-1. The epoxide hydrolase catalyzed the hydrolysis of several epoxides, including epichlorohydrin, epibromohydrin, epoxyoctane and styrene epoxide. With all chiral compounds tested, both stereoisomers were converted. Amino acid sequencing of cyanogen bromide-generated peptides did not yield sequences with similarities to other known proteins.