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 res pired CO2 and biomass has been measured for two types of aerobic bacteria f ound in contaminated land sites. Pseudomonas putida strain NCIMB 10015 was cultured on phenol and benzoate and Rhodococcus sp. I-1 was cultured on phe nol. Results indicate that aerobic isotope fractionations of differing magn itudes occur during aerobic biodegradation of these substrates with an isot opic depletion in the CO2 (Delta(13)C(phenol-CO2)) as much as 3.7 parts per thousand and 5.6 parts per thousand for Pseudomonas putida and Rhodococcus sp. I-1 respectively. This observation has significant implications for th e use of a stable isotope mass balance approach in monitoring degradation p rocesses that rely on indigenous bacterial populations. The effects of the metabolic pathway utilised in degradation and inter-species variation on th e magnitude of isotope fractionation are discussed. Possible explanations f or the observed isotope fractionation include differences in the metabolic pathways utilised by the organisms and differences in specific growth rates and physiology. (C) 1999 Elsevier Science Ltd. All rights reserved.