NADPH-Driven Organohalide Reduction by a Nonrespiratory Reductive Dehalogenase

Area of Science:

• Biochemistry and Environmental Microbiology
• Enzyme catalysis and bioremediation

Background:

• Reductive dehalogenases are crucial enzymes in bacterial organohalide respiration, aiding in the detoxification of hazardous pollutants.
• Studying reductive dehalogenases is often challenging due to low cell yields and oxygen sensitivity.

Purpose of the Study:

• To reconstitute an NADPH-dependent reducing system for the nonrespiratory reductive dehalogenase NpRdhA from Nitratireductor pacificus.
• To investigate the functional requirements for NpRdhA-mediated organohalide reduction in vitro and in vivo.

Main Methods:

• In vitro reconstitution of NpRdhA activity using various reductase and ferredoxin combinations, including Escherichia coli flavodoxin reductase (EcFldr) and spinach ferredoxin (SpFd).
• In vivo functional analysis through coexpression of EcFldr, SpFd, and NpRdhA in Bacillus megaterium.
• Quantification of NADPH consumption under anaerobic and aerobic conditions.

Main Results:

• A nonphysiological system (EcFldr/SpFd) successfully supported NADPH-dependent organohalide reduction by NpRdhA, unlike native N. pacificus components.
• The reconstituted system demonstrated activity under both anaerobic and aerobic conditions with efficient NADPH utilization.
• In vivo coexpression in B. megaterium conferred the ability to reduce brominated substrates, validating the in vitro findings.

Conclusions:

• The study establishes a minimal functional organohalide reduction module comprising EcFldr, SpFd, and NpRdhA.
• This reconstituted system offers a robust platform for studying reductive dehalogenases and developing bioremediation strategies for recalcitrant organohalide pollutants.
• The enzyme's stability under aerobic conditions provides new insights into biological reductive dehalogenase mechanisms.