Analysis of the optimal model for substrate substitutability in continuous microbial cultures

Abstract

A comprehensive model for microbial growth in multiple substrate environment developed by Venkatesh et al. (1997, Biotechnol. Bioengng, 56, 635–644) is applied to growth in continuous cultures and analyzed at steady state. Analytical expressions are derived for substrate concentrations in terms of cellular and reactor parameters. These expressions are seen to describe the substrate utilization pattern and to identify regions of steady state and wash-out for a given feed concentration. These expressions also give the nature of the isoclines just based on simple manipulation of the model equations. The model predictions were compared with experimental data and were found to match reasonably well. Simulations were also performed to get steady-state concentrations of substrates with varying dilution rate. It was seen that in mixed substrate cultures, the system washes out at higher dilution rates than when they were growing on single substrates. The model was extended for microbial growth on various substrate pairs and also on a mixture containing three substrates.