A Two Litre Scale Continuous Culture Apparatus for Micro‐organisms

SUMMARYMethanol-limited cultures of Pseudomonas AM I were grown in chemostats (D, 0.1 h.-l; methanol 10 g./l.) at dissolved oxygen tensions between I and 690 mm. Hg. Decreasing the dissolved oxygen tension from I I O to 2 8 5 mm. Hg did not affect either respiration or carbon balance, but lowering it further caused a progressive increase in respiration which was maximal at 3 mm. Hg (the lowest dissolved oxygen tension at which a steady state could be maintained at the fixed dilution rate). Increasing the dissolved oxygen tension from 97 to 560 mm. Hg increased production of CO, and decreased yield; this effect was particularly evident between 420 and 560 mm. Hg. Yield varied little between 560 and 690 mm. Hg but CO, output decreased and exocellular products increased in concentration indicating a metabolic change. The possible mechanisms involved in metabolic regulation are discussed; it is concluded that dissolved oxygen tensions between 3 mm. and 690 mm. Hg exert a continuous quantitative control over respiration and metabolism of growing organisms. A stoichiometric equation is derived for the growth of Pseudomonas AM I on methanol.

“…A chemostat was used which had a culture vessel similar in design to that of Elsworth, Meakin, Pirt & Capell (1956), and a working volume of 2-75 1. A vaned-disc impeller (64 mm.…”

Section: Continuous Culture Equipmentmentioning

confidence: 99%

The Influence of Dissolved Oxygen on Pseudomonas AM1 Grown on Methanol in Continuous Culture

Maclennan

Ousby

Vasey

et al. 1971

“…'Exponential phase' bacteria were harvested after 3 hr when 40-50 yo of the maximum growth had occurred. In experiments concerned with the effect of growth phase on thermal resistance, bacteria were grown in a batch culture vessel essentially as described by Elsworth, Meakin, Pirt & Capell (1956) a t a continuously maintained pH value of 7-2-704 with adequate aeration (Strange et al 1961). Viability determinations.…”

Section: Organisms Aerobacter Aerogenesmentioning

confidence: 99%

Effects of Thermal Stress on Viability and Ribonucleic Acid of Aerobacter aerogenes in Aqueous Suspension

Strange¹,

Shon²

1964

105

SUMMARYThe death-rate of washed Aerobucter aerogernes in aqueous suspension at 47" depended on the nature of the growth medium, the composition of the liquid used to wash and resuspend the bacteria, the bacterial growth phase, the bacterial concentration in heated suspensions, the pH value, the oxygen tension and the composition of the diluent in which bacteria were heated. The relative resistance of bacteria in different growth phases differed according to the growth medium and the washing fluid; stationary phase bacteria were not more resistant than exponential phase organisms under all conditions. Starvation increased the thermal resistance of exponential and stationary phase bacteria. High bacterial concentration favoured survival a t 47" under most conditions; cell-free filtrate from a heated dense suspension (1010 bacteria/ml.) protected a sparser population of fresh bacteria ( 107-10g/ml.) heated in it. Protective material in filtrate was heat-stable ( 100°/15 min.) and diffused through cellophan. The optimum pH value for survival at 47" was near pH 6-5. Aerobic conditions favoured survival in distilled water but not in salt solutions or phosphate saline (pH 6-5). The effects of various concentrations of NaCl and KC1 on the survival of bacteria at 47' under aerobic conditions were different, K+ concentrations above 0.1 M being more lethal than equivalent concentrations of Na+; the lethal effect of heating in mixtures of these salts (total M > 0.1) increased with K+ concentration. Growth medium, Mg2+ (0-01-5 mM) and, to a lesser extent, Mn*+ (0.5 mM) or Co2+ ( 5 mM) decreased the death-rate, whereas ethylenediamine tetraacetic acid (mM), or various sugars, increased it. Mga+ but not M n 2 + reversed the lethal effect of sugars.Generally, conditions which accelerated the death-rate of Aerobucter wogem?s at 47" also increased the rate of degradation of endogenous RNA. This was accompanied by an increase in the ultraviolet absorption of cold acid-extracts of bacteria and of the suspending fluid. Bacterial protein was degraded to a smaller extent. Depletion of RNA is probably not the primary cause of death a t 47" but the effect on bacterial metabolism of a rapid increase in endogenous pool constituents resulting from RNA degradation may contribute to the lethal effect.

“…The two models have the following features in common. The nutrient medium is supplied to the culture by means of a Sigmamotor peristaltic pump and Revco Zeromax speedchanger (Sigmamotor Inc., Middleport, N.Y., U.S.A.), the rate of medium flow being measured by the rate of filling of a graduated tube as described by Elsworth, Meakin, Pirt & Capell (1956). The medium reservoir, a 10 1. glass bottle, was replenished when necessary by connecting it to a second container filled with sterile medium and transferring the fresh medium by means of sterile compressed air.…”

Section: Continuous Culture Apparatusmentioning

confidence: 99%

The yields of Streptococcus faecalis grown in continuous culture

Rosenberger¹,

Elsden²

1960

136

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.