Identifying competing aerobic nitrobenzene biodegradation pathways by compound-specific isotope analysis

Area of Science:

• Environmental microbiology
• Biogeochemistry
• Isotope geochemistry

Background:

• Nitroaromatic compounds are persistent environmental pollutants.
• Biodegradation of nitroaromatics occurs via multiple pathways, complicating environmental monitoring.
• Distinguishing between aerobic oxidation and partial reduction is crucial for understanding contaminant fate.

Purpose of the Study:

• To differentiate aerobic nitrobenzene oxidation by Comamonas sp. strain JS765 from partial reduction by Pseudomonas pseudoalcaligenes strain JS45.
• To utilize compound-specific stable carbon (¹³C) and nitrogen (¹⁵N) isotope analysis for pathway elucidation.
• To establish a basis for assessing nitrobenzene biodegradation in contaminated environments.

Main Methods:

• Analysis of bulk ¹³C and ¹⁵N enrichment factors (ε) for nitrobenzene transformation.
• Determination of primary apparent kinetic isotope effects (AKIE) for ¹³C and ¹⁵N.
• Comparison of measured isotope effects with proposed reaction mechanisms for each microbial strain.

Main Results:

• Nitrobenzene dioxygenation by JS765 showed distinct ¹³C and ¹⁵N enrichment factors and AKIEs, consistent with ring oxidation.
• Partial reduction by JS45 yielded different ε and AKIE values, supporting a two-electron reduction of the nitro group.
• The study provides characteristic isotopic signatures for each biodegradation pathway.

Conclusions:

• Compound-specific stable isotope analysis is a powerful tool for distinguishing competing nitroaromatic biodegradation pathways.
• The identified ¹³C and ¹⁵N isotope behaviors provide a reliable method for assessing nitrobenzene fate in situ.
• This approach enhances the understanding of microbial remediation strategies for nitroaromatic contamination.