Isotopic composition of inorganic carbon as an indicator of benzoate degradation by Pseudomonas putida: temperature, growth rate and pH effects

Degradation experiments of benzoate by Pseudomonas putida resulted in enzym atic carbon isotope fractionations, However, isotopic temperature effects b etween experiments at 20 and 30 degrees C were minor. Averages of the last three values of the CO2 isotopic composition (delta(13)C(CO2(g))) were more negative than the initial benzoate delta(13)C value (-26.2 parts per thous and Vienna Pee Dee Belenite (VPDB)) by 3.8, 3.4 and 3.2 parts per thousand at 20, 25 and 30 degrees C, respectively. Although the maximum isotopic tem perature difference found was only 0.6 parts per thousand, more extreme tem perature variations may cause larger isotope effects. In order to understan d the isotope effects on the total inorganic carbon (TIC), a better measure is to calculate the proportions of the inorganic carbon species (CO2(g), C O2(aq) and HCO3-) and to determine their cumulative delta(13)C(TIC). In all three experiments delta(13)C(TIC) was more positive than the initial isoto pic composition of the benzoate at a pH of 7, This suggests an uptake of C- 12 in the biomass in order to match the carbon balance of these closed syst em experiments. Copyright (C) 2000 John Wiley & Sons, Ltd.