D-malate production by permeabilized Pseudomonas pseudoalcaligenes; optimization of conversion and biocatalyst productivity

For the development of a continuous process for the production of solid D-m alate from a Ca-maleate suspension by permeabilized Pseudomonas pseudoalcal igenes, it is important to understand the effect of appropriate process par ameters on the stability and activity of the biocatalyst. Previously, we qu antified the effect of product (D-malate(2-)) concentration on both the fir st-order biocatalyst inactivation rate and on the biocatalytic conversion r ate. The effects of the remaining process parameters (ionic strength, and s ubstrate and Ca2+ concentration) on biocatalyst activity are reported here. At (common) ionic strengths below 2 M, biocatalyst activity was unaffected . At high substrate concentrations, inhibition occurred. Ca2+ concentration did not affect biocatalyst activity. The kinetic parameters (both for conv ersion and inactivation) were determined as a function of temperature by fi tting the complete kinetic model, featuring substrate inhibition, competiti ve product inhibition and first-order irreversible biocatalyst inactivation , at different temperatures simultaneously through three extended data sets of substrate concentration versus time. Temperature affected both the conv ersion and inactivation parameters. The final model was used to calculate t he substrate and biocatalyst costs per mmol of product in a continuous syst em with biocatalyst replenishment and biocatalyst recycling. Despite the ef fect of temperature on each kinetic parameter separately, the overall effec t of temperature on the costs was found to be negligible (between 293 and 3 08 K). Within pertinent ranges, the sum of the substrate and biocatalyst co sts per mmol of product was calculated to decrease with the influent substr ate concentration and the residence time. The sum of the costs showed a min imum as a function of the influent biocatalyst concentration. (C) 2000 Else vier Science B.V. All rights reserved.