Variation in stable carbon isotope fractionation during aerobic degradation of phenol and benzoate by contaminant degrading bacteria

Variation in the natural abundance stable carbon isotope composition of respired CO2 and biomass has been measured for two types of aerobic bacteria found in contaminated land sites. Pseudomonas putida strain NCIMB 10015 was cultured on phenol and benzoate and Rhodococcus sp. I1 was cultured on phenol. Results indicate that aerobic isotope fractionations of di€ering magnitudes occur during aerobic biodegradation of these substrates with an isotopic depletion in the CO2 (D Cphenol-CO2) as much as 3.7and 5.6for Pseudomonas putida and Rhodococcus sp. I1 respectively. This observation has signi®cant implications for the use of a stable isotope mass balance approach in monitoring degradation processes that rely on indigenous bacterial populations. The e€ects of the metabolic pathway utilised in degradation and inter-species variation on the magnitude of isotope fractionation are discussed. Possible explanations for the observed isotope fractionation include di€erences in the metabolic pathways utilised by the organisms and di€erences in speci®c growth rates and physiology. # 1999 Elsevier Science Ltd. All rights reserved.