Bacterial growth as an optimal process

Abstract

A mathematical model containing all the characteristic features of batch microbial growth (lag, exponential growth, stationary and decline phases) is here developed. The model is based on the assumption that the growth rate is controlled by the amount of some critical intermediate produced by the organism and the consequences of the assumption that the production of this is so regulated as to produce the maximum cellular mass by the time the limiting nutrient is exhausted are explored. In spite of its simplicity this model gives a sound qualitative agreement with observations of the developments that occur in microbial cultures, the lag phase being the result of the cell first building up its supply of the critical intermediate. Literature reports suggest that the cellular component that is comparable in behavior to the substance which controls the production of this intermediate is the total ribonucleic acid or ribosomal ribonucleic acid fraction. Both increase during the lag phase, remain fairly constant (on a per dry weight of cell basis) during the growth phase, and decrease in the stationary and decline phases. Since most of the RNA is found in the ribosomes, the sites of protein synthesis, this implies that the critical intermediate required for growth is protein.