Branched pathways in the degradation of cDCE by cytochrome P450 in Polaromonas sp. JS666

- Degradation of cDCE and 1,2-DCA catalyzed by cytochrome P450 in Polaromonas sp. JS666
- The same enzyme-catalyzed pathway can produce different products with distinct ε values.
- Observed ε values will be a weighted average that reflect the product ratios.

Compound specific isotope analysis (CSIA) is widely used to monitor contaminant remediation in groundwater. CSIA-based approaches that use enrichment (ε) values to assess degradative processes rely on the assumption that the contaminant being investigated will have an ε value that is constant and specific to a catalytic pathway of a microorganism. Distinct ε values have been reported for aerobic degradation of cis-dichloroethene (cDCE), which has led to a number of proposed degradation mechanisms; however, cytochrome P450 catalyzed oxidation is the only biochemical mechanism that has been established in Polaromonas sp. JS666. Using CSIA we measured the ε values for microbial oxidation of cDCE (− 18.8‰ ± 1.5‰) and 1,2-dichloroethane (1,2-DCA) (− 16.6‰ ± 0.9‰) in wild-type JS666 and the oxidation of cDCE (− 13.5‰ ± 2.3‰) from a recombinant E. coli strain expressing the cytochrome P450 enzyme from JS666. This study supports the hypothesis that cytochrome P450 catalyzes the initial step in the degradation pathway of both cDCE and 1,2-DCA and provides evidence that a single enzyme can catalyze multiple pathways with different products and distinct ε values for a single substrate. Therefore, in cases where the products of the reaction cannot, or have not been characterized, caution must be used when employing ε values to interpret mechanisms, pathways, and their applications to environmental contaminant remediation.

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