Patent GB-1525535-A (GB)
Title: Process for culturing cells
IPC: C12M1/00
Filed: 1976-04-02
Abstract: 1525535 Regulating fermentations; tissue culture; methanol-utilizing bacteria IMPERIAL CHEMICAL INDUSTRIES Ltd 23 March 1977 [2 April 1976 8 Dec 1976] 13442/76 and 51198/76 Heading C6F The invention is based on the theory that where growing organisms are supplied with a carbon and/ or energy source such that periods of energy starvation occur, when energy is supplied to the cells after a period of energy starvation a proportion of that energy supplied is initially used by the cells in a period of adaptation to a growing state and is therefore effectively not available for efficient growth. Cells subjected to a truly continuous supply of an energy source (such as a carbon source) grow in a truly steady state where metabolite pools and enzyme activities are at effectively constant levels commensurate with efficient biomass formation. Such cultures can be made inefficient by supplying the energy source in pulses separated by time intervals. Fig. 2 depicts graphs of biomass efficiency ratio (ordinate) i.e. the ratio of the observed energy conversion efficiency of a biological system, obtained in an environment subjected to an intermittent availability of energy, to the energy conversion efficiency of a similar system subjected to continuous availability of energy source, versus cycle time (abscissa-log scale) i.e. pulse time plus the following time interval during which no exogenous energy is available to the culture before the next energy supply, for various values of the ratio Á/Á max  Á being the imposed overall specific growth rate and Á max  the maximum specific growth rate attainable by that culture when unlimited by the availability of carbon and energy source. The specification details suitable values of the ratio Á/Á max  in relation to cycle times for various types of fermentations. Broadly, brief cycle times are best suited for processes involving the production of single cell protein and extended cycle times for the production of extracellular and intracellular metabolites e.g. citric acid, amino acids and antibiotic substances. Intermediate values corresponding to the 'dip' in the graphs (reduced efficiency) are more appropriate to the biological treatment of waste-water where it is desirable that sludge production should be reduced to a minimum, aerobic processes producing CO 2  and the microbiological production of simple organic molecules (specified). The energy source may be the carbon substrate, a light source in the case of photosynthetic reactions, hydrogen in cultures which can utilize hydrogen as an energy source and other reduced inorganic energy sources with chemolithotropic micro-organisms. The energy may be supplied to a culture, for example in a tank fermenter, in pulses separated by intervals of time, regularly or irregularly. Alternatively, there may be spatial intervals between successive energy supply points to a culture flowing along a pathway defined by physical constraints, the energy being supplied continuously or in pulses separated by intervals of time at the spaced supply points. The process is applicable to the culturing of bacteria, yeasts, fungi, and also tissue cells. The Examples are directed to the regulated cultivation of strains of Methylophilus methylotrophus (previously known as Pseudomonas methylotropha) upon methanol substrates.