On nitroaryl reductase activities in several Clostridia

Area of Science:

• Microbiology
• Enzymology
• Biochemistry

Background:

• Clostridia are known for diverse metabolic capabilities, including redox reactions.
• The reduction of nitroaromatic compounds is important in microbial metabolism and bioremediation.
• Specific enzymes responsible for nitro group reduction in Clostridia have not been well-characterized.

Purpose of the Study:

• To identify and characterize enzymes in Clostridia that reduce the nitro group of p-nitrobenzoate.
• To investigate the electron donors and cofactors involved in this reduction.
• To differentiate these reductases from other known enzymes within Clostridia.

Main Methods:

• Crude extracts of Clostridia species (C. kluyveri, C. spec. La 1, C. sporogenes, C. pasteurianum) were used to assay nitro group reduction.
• NADH and pyruvate were tested as electron donors.
• Enzymes were partially purified from C. kluyveri and characterized using chromatographic behavior, stability, pH optima, molecular masses, and EPR studies.
• Comparison with known dehydrogenases and reductases was performed.

Main Results:

• Crude extracts of Clostridia catalyzed NADH-dependent reduction of p-nitrobenzoate.
• Pyruvate served as an additional electron donor for C. kluyveri, C. spec. La 1, and C. sporogenes.
• Partially purified NADH-dependent nitroaryl reductases from C. kluyveri were distinct from other characterized dehydrogenases.
• The initial step of the reduction involves a nitroradical anion (1 electron transfer).
• 2-oxo-acid synthases also showed low rates of p-nitrobenzoate reduction.

Conclusions:

• Clostridia possess previously unknown pyridine nucleotide-dependent nitroaryl reductases.
• These enzymes are distinct from known dehydrogenases and reductases in Clostridia.
• The physiological roles of these nitroaryl reductases remain to be elucidated.