MULTIPHASIC KINETICS CAN BE AN ARTIFACT OF THE ASSUMPTION OF SATURABLE KINETICS FOR MICROORGANISMS

Much of the evidence for the application of Michaelis-Menten kinetics to bacterial suspensions is derived from Wright-Hobbie plots of radion uclide uptake and incorporation rates in the presence of naturally occ urring concentrations of substrates. It is shown that the same data us ed to support saturation models can also be fitted by a diffusion-base d transport equation. Mixed, pure and natural assemblages of microorga nisms were used to study glucose uptake and thymidine and leucine inco rporation. Multiphasic kinetics for glucose uptake by mixed cultures w as observed when data were plotted on a Wright-Hobbie plot (K+S values of 2.7, 37 and 3500 muM), but the dif fusion model fit data with a si ngle set of coefficients over a 6 orders of magnitude range in glucose concentrations. It is suggested that diffusive transport into the cel l is dominant at the relatively high thymidine and leucine concentrati ons used in bacterial production studies, and that non-saturable diffu sive transport contributes to widely varying bacterial conversion fact ors.