Substrate inhibition in Pseudomonas oxalaticus OX1: a kinetic study of growth inhibition by oxalate and formate using extended cultures

Pseudomonas oxalaticus OX1 has been grown in a mineral salts medium with oxalate or formate as the sole source of carbon and energy. At concentrations of these substrates above 50 mM inhibition of growth was indicated by a long and variable lag phase in batch culture. This inhibition was further studied by estimating maximum specific growth rates at different substrate concentrations using the extended culture technique for control of the substrate concentration. With formate, inhibition became apparent at substrate concentrations above 20 mM, whereas oxalate inhibited growth at concentrations above 15 mM. Complete inhibition was not observed even at concentrations of 100 mM. A number of inhibition functions were fitted with the experimental data using computer analysis. The results indicated that the Haldane equation was the simplest function to describe quantitatively the kinetics of the observed substrate inhibition. Studies on the rate of oxygen uptake at different concentrations of oxalate indicated that respiration was much more sensitive to inhibition than growth. However with formate, inhibition of respiration was not observed up to concentrations of 50 mM, indicating that different mechanisms may underlie the observed growth inhibition by the two substrates.