Retrospective on microbial transformations of halogenated organics.

Area of Science:

• Environmental microbiology
• Bioremediation
• Halogenated compound transformation

Background:

• Limited understanding of biological transformations of highly halogenated aliphatic compounds before the 1960s.
• Early observations of limited abiotic and mammalian enzymatic transformations.
• Prevailing belief that aerobic cometabolism occurred, while anaerobic transformations were thought to be absent.

Purpose of the Study:

• To investigate the occurrence and mechanisms of microbial dehalogenation of halogenated compounds.
• To understand the energetic basis for microbial dehalogenation.
• To explore the application of dehalogenating microorganisms in environmental remediation.

Main Methods:

• Discovery and characterization of microorganisms capable of dehalogenation.
• Investigation of metabolic pathways, including cometabolism and reductive dehalogenation.
• Enrichment and isolation of anaerobic bacteria utilizing halogenated compounds.

Main Results:

• Identification of anaerobic microbial dehalogenation of chlorinated pesticides and solvents starting in the late 1960s and early 1980s.
• Discovery in the 1990s of bacteria that gain energy from anaerobic transformations, enabling complete dechlorination.
• Demonstration that many species use molecular hydrogen as a donor and halogenated organics as electron acceptors for energy conservation via reductive dehalogenation.

Conclusions:

• Significant advancements in understanding microbial dehalogenation since the 1960s.
• Reductive dehalogenation by specialized bacteria is a key mechanism for complete detoxification.
• Widespread application of these microorganisms for hazardous halogenated chemical remediation in contaminated groundwater is ongoing.