The yields of Streptococcus faecalis grown in continuous culture

Abstract

SUMMARY:Streptococcus fuecalis has been grown anaerobically in continuous culture on a defined medium. Under these conditions it is possible to maintain (a) the glucose concentration, (b) the tryptophan concentration, and (c) the generation time a t predetermined values, and to study the effects of changes in these variables on the culture. When growth was limited by the glucose supply, the glucose yield constant (dry weight of cells €'ormed/weight of glucose used) was greater than when tryptophan was limiting. The glucose yield constant under conditions of tryptophan limitation progressively fell with increasing supplies of glucose until it reached a minimum value. Under conditions of tryptophan limitation and large excess of glucose, the amount of glucose used per unit weight of cells per unit time remained roughly constant irrespective of growth rate. It is concluded that the needs of cell synthesis in S. fueculis do not control the rate of glucose breakdown, i.e. the rate of the energy-yielding metabolism. At slow growth rates the end products of glucose metabolism included volatile fatty acids, which were not present, or present in small amounts, a t faster growth rates.In the course of his studies of the factors which control the growth of bacteria Monod (1942) established that, when the energy source is the limiting nutrient, the quotient-weight of cells produced/weight of energy source used-is constant irrespective of the concentration of the carbon source. This quotient is referred to as the growth yield constant (GYC). Monod also showed that there is a simple relationship between the specific growth rate and the concentration of the growth-limiting nutrient. The saturation constant, i.e. the concentration of the limiting nutrient at which the specific growth rate is half maximal, is very low and Monod obtained values of 4 , 2 and 25 mg/l. for glucose, mannitol and lactose respectively, as carbon sources for Escherichia coli.In all, Monod studied three organisms, Escherichia coli, Bacillus subtilis and Salmonella typhimurium. Monod's findings have been repeatedly confirmed by other microbiologists using other organisms grown batchwise upon a wide range of energy sources and the constancy of the GYC of a given organism grown on a particular energy source can be taken as established. However, it is important to realize that the values obtained by the various workers apply solely to the particular conditions employed, i.e. to growth in batch culture with the substrate in question the factor limiting growth and all other essential nutrients present in excess, It is clear from what has been said above that, under these conditions, the specific growth rate is maximal for almost the whole period of growth.

Diketocamphane enantiomer-specific "Baeyer-Villiger" monooxygenases from camphor-grown Pseudomonas putida ATCC 17453

“…Cultures were grown aerobically at 30 "C. Basal media contained (g 1-'): KH,PO,, 2; Na,HPO,, 4; (NH4),S04, 1 ; and 4ml trace metal stock solution (Rosenberger & Elsden, 1960). Camphor was added at 2.5 g 1-' before autoclaving.…”

Ring cleavage reactions in the metabolism of (-)-menthol and (-)-menthone by a Corynebacterium sp.

“…Cultures were grown aerobically at 30 "C. Basal media contained (g 1-' ) : KH,PO,, 2 ; Na,HPO,, 4; (NH,),SO,, 1 ; and 4 ml trace-metal stock solution 1-' (Rosenberger & Elsden, 1960). (-)-Menthol and (-)-menthone (0.25 g 1-' ) were added directly to the sterilized basal medium.…”

Regulation of energy source metabolism in streptococci

“…Under glucose-limited conditions, however, the intracellular con- For an excellent review of this topic, the reader is degradation of glucose can be observed. It was already mentioned above that Rosenberger and Elsden (1960) observed a referred to Hugenholtz (1993). If citrate is metabolized in the presence of another energy 92-95% conversion of glucose into lactate at the highest growth rate tested.…”