'Growth of bacterial cultures' 50 years on: towards an uncertainty principle instead of constants in bacterial growth kinetics.

Ever since Monod's efforts to study bacterial cultures in quantitative terms, the growth of Escherichia coli on sugars like glucose has appeared an attractive subject for the mathematical description of nutrient conversion into biomass. But instead of simplicity, it is becoming evident that bacterial adaptations affect 'constants' such as K(s) (growth affinity constant) and are, in turn, a complex function of nutrient concentration. Instead of a single affinity, bacteria exhibit a continuum of nutrient scavenging abilities peaking at micromolar sugar levels; there is lower affinity with millimolar or submicromolar glucose in the medium. Similar problems arise in defining parameters such as Y (growth yield constant), because nutrient-limited growth at low exponential growth rates induces a continuum of hunger and starvation responses. Autocatalytic changes to the environment caused by growth (as well as external factors) ensure that bacteria present an ever-adapting interface to the outside world. The regulatory interaction between the organism and environment means that no universal kinetic constants describe bacterial growth.