The content of total, bound and osmotically free magnesium was estimated in various fungi and in the yeast Saccharomyces cerevisiae. Total magnesium increases at lower growth rates of Endomyces magnusii and Penicillium chrysogenum 140A as well as during the logarithmic stage of growth of Penicillium chrysogenum Q-176. The binding of magnesium requires orthophosphate, decreasing during lack of external phosphate when the intracellular concentration of free magnesium rises. The fungi were found to contain a novel form of bound magnesium, a polymeric magnesium orthophosphate (PO Mg), which appears to take part in the control of free magnesium level in Penicillium chrysogenum Q-176. The level of free magnesium is proportional to the growth rate of Endomyces magnusii and Penicillium chrysogenum Q-176 and 140A. Total, as well as free, magnesium changes less than three-fold as external Mg concentration is changed 13,000-fold. The magnesium is taken up against concentration gradients of 1 : 25 to 1 : 1300, the metal being distributed non-uniformly in the cells of Saccharomyces cerevisiae.
This article proposes a new approach to the modeling of continuous cultures of microorganisms based on the concept of universality classes. Instead of analysis of concrete sets of equations, vast classes including models with identical qualitative features should be studied. The class of models of the second order is the simplest one, and it is analyzed in order to demonstrate the mathematical methods used. The authors have shown that the simplest model usually used for the description of continuous cultures is sensitive to even slight modifications. The modified model changes its properties and gives rise to a class of models that are applicable to the description of damped and nondamped oscillations of biomass and substrate concentrations in a fermenter. Irrespective of the mode of the initial model modification, the oscillations have a number of common features. These features can be used as the criteria of utility of this class of models for simulation of culture behavior. Two models of the class in question (with nonzero maintenance coefficient and nonconstant yield) are analyzed using these criteria.
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