[Changes in the physiologic properties of a chemostat culture of Propionibacterium shermanii during growth limitation by a deficiency of sodium lactate].
A chemostat curve has been constructed for changes in the Propionibacterium shermanii population density with an increase in the flow rate of the medium from 0.04 to 0.55 h-1 upon limitation of the growth with sodium lactate deficiency. The curve differs from the classic chemostat curve described with the Monod equation, thus indicating changes in metabolism at different growth rates. Fermentation of lactate to acetic and propionic acids by the culture is most complete at low flow rates of the medium (D = 0.04 h-1). The rates of oxidation processes increase at average flow rates (D = 0.1--0.33 h-1). Lactate is both fermented to yield volatile acids, and oxidized. The growth rate D = mu = 0.55 h-1 approaches the maximal one. The rate of fermentation by the culture at this growth rate decreases while the rate of oxidation increases. The ratio between the rates of these two processes shifts towards oxidation. The cells display now a very high synthetic activity: constructive metabolism of the cells is realized practically only at the account of the nitrogen from ammonium rather than the nitrogen of amino acids. The chemical composition of the cells along the chemostat curve is relatively constant. The content of protein and DNA does not change; the content of RNA slightly rises with an increase in the growth rate, and the protein synthesizing activity of RNA is directly proportional to D = mu.