[Theoretical determination of the energy efficiency of microbial carbon substrate conversion and comparison with experimental values in phase cultures]. / Theoretische Bestimmung energetischer Wirkungsgrade der mikrobiellen Kohlenstoffsubstratwandlung und Vergleich mit experimentellen Werten an Phasenkulturen.

The phenomenological description of microbial substrate conversion is possible by connecting energy and material balance equations. The change of free enthalpy of microbial substrate conversion was determined on the basis of exact material balance equations. A simultaneous determination of heat production allowed to calculate the energetic efficiency of microbial growth processes. In addition to this the change of free enthalpy by microbial substrate conversion was standardized by the free standard formation enthalpy of biomass. Both quantities were used for comparing microbial combustion of several substrates into biomass. Comparable with the concept of substrate combustion enthalpy standardized by the combustion enthalpy of biomass an optimal strategy of mixing different substrates can be deduced from energy and material balance equations on the basis of theoretic consumption coefficients. Besides the energetic efficiency the binding state of the substrate is important in the search for optimal substrate mixing ratios. This could be shown by experimental work. Thus, the fermentation systems sucrose/yeast, paraffin/yeast, and sucrose/paraffin/yeast were studied using synchronous populations produced by the method of phased cultures. The investigations of real fermentation systems confirm the theoretical predictions on special conditions.

Yield coefficients in dependence on milieu conditions and cell states. III. Induction of synchrony in continuous yeast cell cultivation by milieu changes.

Induction of synchrony by various perturbations in continuous yeast cultivation on hydrocarbons of crude oil is described. Short-time temperature and pH-value shocks cause oscillations of budding cell percentage in the order of the cell cycle duration. An abrupt change of the phosphate ion concentration of the nutritional medium may also induce a synchronization of microbial growth. However, the frequency corresponds with the eigenfrequency of the fermentation process. The experimental values were investigated statistically using autocorrelation and spectral analysis.

Yield coefficients in dependence on milieu conditions and cell states. II. Influence of perturbations on continuous cultivation of the yeast Lodderomyces elongisporus on hydrocarbons.

The influence of perturbations on continuous yeast cell cultivations on hydrocarbons of crude oil is described. Due to such perturbations the fermentation system leaves its steady state, passes through transitional stages and reaches a new steady state. In the transitional stages a damped oscillation of biomass concentration, percentage of budding cells, oxygen consumption rate, and heat flow is observed. These results can be explained by partial synchronization of yeast cell functions in microorganism populations. In phases of partial synchronization the cell cycle of a single cell is reflected by the behaviour of the microorganism population. The adaptation of the carbon substrate feeding rate to the state of partially synchronized microorganism population makes possible lower specific substrate consumption in biomass production.

[Thermodynamics of microbial processes]. / Thermodynamik mikrobieller Prozesse.

The unique description of the dependences of the specific consumption coefficients on the process state known from the literature is an important prerequisite to the further increase of the intensity and efficiency of the process for the industrial protein synthesis. Suitable measuring quantities for it are entropy production, an important quantity of thermodynamics of irreversible processes, and differential heat flow which can be measured by microcalorimetry. The description of the dependences of consumption coefficients by thermodynamics of irreversible processes allows an ingenious statement of calorimetric measurements of the fermentation process to confirm and to make precise the knowledge deduced from thermodynamics. Thermodynamical considerations and calorimetric measurements are used to describe the dependences of consumption coefficients on substrate concentration, nature of limitation, and periodical perturbations of the process.

[Effect of alternating milieu changes on specific substrate consumption in microorganisms]. / Einfluss alternierender Störungen auf die Verbrauchskennziffern beim Wachstum von Mikroorganismen.

In technical microbiology microorganisms often undergo alternating milieu changes. For instance, this is the case in recirculation reactors. The organisms react on these changes with an increase of entropy production and in connection with this with increasing substrate consumption. This increasing substrate consumption contradicts the aim of an optimum yield from a given substrate. Thus, studies of the reaction of microbial growth to alternating milieu changes are of great importance. A simple model of the influence of alternating milieu changes on specific substrate consumption is given. In it the biological conversion of substances is built up by an irreversible consecutive reaction. After preliminary examinations on the analogue computer the reaction of the model to alternating perturbations is simulated on the digital computer. The results of the stimulations are compared with experimental data. The good agreement of experiment and model justifies the use of the simple formulation in the preparation of technical processes.