Modelling of Physiological Control of Production of Exocellular Hydrolytic Enzymes

Abstract

The rate of production of several exocellular hydrolytic enzymes (e.g. amylases, lipases and several proteinases) is generally connected with physiological functions coupled with growth. In this paper an attempt has been made to design a mathematical model of an observed kinetic of enzyme production. Figure 1 shows the typical course of growth and enzyme production during batch culture. From the viewpoint of microbial physiology the course of growth and enzyme production can be split into four regions. In region I the lag in growth and enzyme formation is observed. In region II the growth is maximal while the production is delayed and has a transient character. In region III the growth is slower due to exhaustion of the limiting substrate but the rate of enzyme formation is at its maximum. The transient period of growth is short but most of hydrolytic enzymes are produced during that period. When the limiting substrate is exhausted the growth ceases and the rate of enzyme production can be zero or negative due to decay processes. The kinetics of decay in this period of cultivation is usually of first order [1] with a half-time of 5–8 hours. Only some extracellular enzymes, whose synthesis proceeds during sporogenesis (e.g. serine proteinase in Bacillus subtilis) are produced by non-growing populations.