BIODEGRADATION OF INDIVIDUAL AND MULTIPLE CHLORINATED ALIPHATIC-HYDROCARBONS BY METHANE-OXIDIZING CULTURES

The microbial degradation of chlorinated and nonchlorinated methanes, ethanes, and ethenes by a mixed methane-oxidizing culture grown under chemostat and batch conditions is evaluated and compared with that by two pure methanotrophic strains: CAC1 (isolated from the mixed culture ) and Methylosinus trichosporium OB3b, With the exception of 1,1-dichl oroethylene, the transformation capacity (T-c) for each chlorinated al iphatic hydrocarbon was generally found to be in inverse proportion to its chlorine content within each aliphatic group (i.e., methanes, eth anes, and ethenes), whereas similar trends were not observed for degra dation rate constants, T-c trends were similar for all methane-oxidizi ng cultures tested, None of the cultures were able to degrade the full y chlorinated aliphatics such as perchloroethylene and carbon tetrachl oride, Of the four cultures tested, the chemostat-grown mixed culture exhibited the highest T-c for trichloroethylene, cis-1,2-dichloroethyl ene, tetrachloroethane, 1,1,1-trichloroethane, and 1,2-dichloroethane, whereas the pure batch-growth OB3b culture exhibited the highest T-c for all other compounds tested, The product toxicity of chlorinated al iphatic hydrocarbons in a mixture containing multiple compounds was cu mulative and predictable when using parameters measured from the degra dation of individual compounds, The T-c for each chlorinated aliphatic hydrocarbon in a mixture (T-c(mix)) and the total T-c for the mixture (Sigma T-c(mix)) are functions of the individual T-c, the initial sub strate concentration (S-0), and the first-order rate constant (k/K-s) of each compound in the mixture, indicating the importance of identify ing the properties and compositions of all potentially degradable comp ounds in a contaminant mixture.