The Continuous Culture of Bacteria; a Theoretical and Experimental Study

Abstract

SUMMARY: A theoretical treatment of continuous culture is given, which allows quantitative prediction of the steady-state concentrations of bacteria and substrate in the culture, and how these may be expected to vary with change of medium, concentration and flow-rate. The layout and operation of a small pilot plant for the continuous culture of bacteria are described. This plant has been operated continuously for periods of up to 4 months without breakdown or contamination of the culture. No alterations in the properties of the organisms studied have occurred during such periods of continuous culture. Results are given of a series of experiments on the continuous culture of Aerobacter cloacae in a chemically defined medium, designed to allow quantitative comparison with the results predicted by the theory. The relative advantages of batch and continuous culture as production processes are discussed, and it is concluded that continuous culture may usually be expected to show a five to tenfold increase in output as compared with a batch process.The continuous culture of micro-organisms is a technique of increasing importance in microbiology. The essential feature of this technique is that microbial growth in a continuous culture takes place under steady-state conditions; that is, growth occurs a t a constant rate and in a constant environment. Such factors as pH value, concentrations of nutrients, metabolic products and oxygen, which inevitably change during the ' growth cycle ' of a batch culture, are all maintained constant in a continuous culture; moreover, they may be independently controlled by the experimenter. These features of the continuous culture technique make it a valuable research tool, while it offers many advantages, in the form of more economical production techniques, to the industrial microbiologist. Nevertheless, the technique has so far been comparatively little used. (The review of Novick (1955) lists nearly all the work on the subject that has yet appeared.) The reasons for this relative neglect are, we believe, twofold.The first reason is the lack of a generally accepted theoretical background. Continuous culture presents theoretical problems of an essentially kinetic nature which must be solved before the technique can be intelligently applied.

On the stable size distribution of populations reproducing by fission into two unequal parts

“…Equations (5.1) and (5.2) happen to be the equations originally found by Monod (see e.g. [12]). They have been extensively investigated by Hsu et al [13] (who deal with the more general situation that several species are competing for nutrients), and for the following we refer to their paper.…”

“…In this paper we consider a continuous culture (see [12]) of proliferating cells which are assumed to be characterized by their size alone. Here "size" can be replaced by any other quantity obeying a physical conservation law, for instance weight or protein content.…”

“…(See e.g. [12]. ) We assume that the individuals of the cell population are characterized by their size x only.…”

A New Kinetic Model of a Growing Bacterial Population

“…Specific applications of the theory to continuous chemical reactions and continuous culture have also been published by Denbigh (1944Denbigh ( , 1947, Monod (1950) ~ Novick & Szilard (1950), Danckwerts (1954), Denbigh & Page (1954), Spicer (1955), Herbert, Elsworth & Telling (1956), Perret (1956Perret ( , 1957) and Moser (1957). The initial section of this paper starts with a non-mathematical description of the properties of simple open systems, based on the publications cited above (particularly those of Burton, 1939 andDenbigh et al 1948).…”

Microbioreactors for Bioprocess Development

“…After about 80 hours, DO, pH, and OD 6oonm reached stable levels and steady state conditions in the microchemostat were established. The net increase rate of bacterial biomass in suspension X is given by the simple mass balance (Herbert et al, 1956):…”