RDases

RDases, short for reductive dehalogenases, are a class of cobamide-dependent enzymes that drive reductive dechlorination during organohalide respiration in anaerobic bacteria. They enable certain microbes to use chlorinated solvents such as perchloroethene (PCE), trichloroethene (TCE), and vinyl chloride as terminal electron acceptors, ultimately producing less-chlorinated compounds or ethene.

Most RDases are multi-component enzymes composed of a catalytic subunit encoded by rdhA genes and often a membrane-anchoring or electron-transfer partner encoded by related genes such as rdhB. The catalytic subunit contains a corrinoid (vitamin B12) cofactor and multiple iron-sulfur clusters that facilitate electron transfer to the bound organohalide. Substrate binding and dechlorination occur in a way that replaces a chlorine atom with a hydrogen atom, generating progressively dechlorinated products. Electron delivery typically comes from cellular donors such as hydrogen or reduced ferredoxin, routed through dedicated electron transfer proteins.

RDases have a broad substrate range that includes PCE, TCE, cis- and trans-dichloroethenes, vinyl chloride, and other halogenated alkanes. They function under strictly anaerobic conditions and depend on the availability of suitable electron donors, cofactors, and regulatory signals that control rdhA expression in response to environmental organohalides.

Ecologically, RDases play a central role in the degradation of chlorinated solvents in subsurface environments. They are found in organohalide-respiring bacteria, including Dehalococcoides mccartyi and related genera, where different RDases confer distinct or overlapping substrate specificities. This diversity underpins bioremediation strategies that stimulate native communities or introduce cultures capable of complete dechlorination from PCE to ethene.

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