Isotopic fractionation of carbon and chlorine by microbial degradation of dichloromethane

Microbial culture experiments were performed at 22°C to investigate isotopic fractionation of carbon (C) and chlorine (Cl) during aerobic degradation of dichloromethane (DCM) by MC8b, a gram-negative methylotrophic organism closely related to the genera Methylobacterium or Ochrobactrum. Values of the isotopic fractionation factor, α, were estimated from the experimental results. These values are 0.9576±0.0015 for C and 0.9962±0.0003 for Cl, corresponding to kinetic isotope effects (KIE) of 1.0424 for C and 1.0038 for Cl. The C isotope effect accompanying aerobic degradation of DCM by MC8b is roughly twice that resulting from microbial oxidation of CH4. Further studies of this type, for a variety of chlorinated aliphatic hydrocarbons (CAHs) under a range of biogeochemical conditions, may find important applications in the characterization and remediation of sites contaminated with CAHs.