Modeling solid-to-solid biocatalysis: Integration of six consecutive steps

A quantitative model for the conversion of a solid-substrate salt to a soli d-product salt in a batch bioreactor seeded with product crystals is presen ted. The overall process consists of six serial steps (with dissolution and crystallization each in themselves complex multistep processes): solid-sal t dissolution, salt dissociation into an ionic substrate and a counter-ion, bioconversion accompanied by biocatalyst inactivation, complexation of the ionic product with the counter-ion, and salt crystal growth. In the model, the consecutive steps are integrated, including biocatalyst inactivation a nd assuming that salt dissociation and complexation of ions are at equilibr ium. Model parameters were determined previously in separate independent ex periments. To validate the model, either dissolved or solid Ca-maleate was converted to solid Ca-D-malate by permeabilized Pseudomonas pseudoalcaligen es in a batch bioreactor seeded with Ca-D-malate crystals. The model very w ell predicted the concentrations of ail components in the liquid phase (Cam aleate, Ca2+, maleate(2-), D-malate(2-), and Ca-D-malate) and the amounts o f the solid phases (Ca-maleate . H2O and Ca-D-malate . 3H(2)O), especially when high initial amounts of Ca-maleate . H2O and Ca-D-malate . 3H(2)O were present. (C) 2000 John Wiley & Sons, Inc.