Specific Glucose Uptake Rate Research Articles

A model for glucose metabolism in energy-sufficient bacterial cultures

A model for uncoupled glucose uptake under energy-sufficient conditions is presented. The model is derived from glucose catabolic pathways. The resulting model predicts specific glucose uptake rate as a function of both growth rate and extracellular glucose concentration. This prediction is consistent with reported literature data.

Water relations of solute accumulation in Pseudomonas fluorescens.

When Pseudomonas fluorescens was grown in a glucose salts medium adjusted with NaCl to a water activity (aw) value of 0.980, the intracellular glutamic acid concentration increased 23-fold and comprised 90% of the total amino acid pool. This increase was not observed when the aw of the medium was reduced to 0.980 with sorbitol. Sorbitol was taken up rapidly over a 30 min period and accumulated intracellularly to a level approximately two-fold greater than the concentration in the growth medium. In continuous culture, the specific rate of glutamic acid production and glucose uptake was greater at 0.980 (NaCl) than at 0.997 aw. The maintenance coefficients for glucose uptake were similar at both aw values but were 2.4-fold greater for glutamic acid production at 0.980 (NaCl) than at 0.997 aw.

Water relations of ethanol fermentation by Saccharomyces cerevisiae: Glycerol production under solute stress

The effect of water activity ( a w ) upon glycerol production during ethanol fermentation by Saccharomyces cerevisiae was studied in continuous culture using sorbitol to adjust the a w to 0.971. A reduction of the a w of the medium resulted in more glycerol being produced. The glycerol yield was 3–4-fold greater at 0.971 a w than 0.994 a w . Ethanol yield and specific rate of ethanol production was slightly greater at 0.971 than 0.994 a w whereas the biomass concentration was lower. Reduced a w increased the specific rate of glucose uptake and the maintenance requirements of the organism. The results suggest that the effect of a w on glycerol production can be reduced by controlled feeding of substrate during fermentation.

The effect of CO2 ventilation on kinetics and yields of cell-mass and ethanol in batch cultures ofZymomonas mobilis

The effect of CO2 removal by continuous sparging of N2 in batch cultures ofZymomonas mobilis (ATCC10988) was examined. N2 sparging considerably reduces lag times in batch cultures, possibly because of continuous removal of CO2 from the culture media. Ventilation of CO2 from culture media results in an increase of about 15% in the average specific growth rate and about 12% in the cell-mass yield with no noticeable trend in the average specific glucose uptake and ethanol production rates. The overall ethanol yield on glucose, however, decreases slightly by 5%. Analysis of ventilated experiments show that the CO2 production is directly coupled with the ethanol formation but not necessarily with the cell-mass production, indicating a decoupling of growth from ethanol production. Further, comparison of ventilated and non-ventilated experiments rules out the possibility of CO2 accumulation in the culture media as a factor responsible for increasing growth inhibition and decoupling of growth from ethanol fermentation at increasing initial glucose concentrations in batch cultures.

Effect of carbon dioxide on growth of Zymomonas mobilis in continuous culture

Biomass production of Zymomonas mobilis in continuous cultivation on synthetic or complex glucose media was increased up to 100% when CO2 partial pressure was reduced from 1,460 to 95 mbar at high dilution rates. Biomass yield increased and specific glucose uptake and ethanol production rates decreased approximately 6% when pCO2 was lowered from 1,160 to 95 mbar. Product yield was not affected by pCO2. Long time adaptation superimposing these effects was considered.

Kinetics of ethanol production from Jerusalem artichoke juice with some Kluyveromyces species

The kinetics of ethanol production by Kluyveromyces marxianus ATCC 12708 and ATCC 10606, K. cicerisporus ATCC 22295 and K. fragilis 105 have been studied using raw juice of the Jerusalem artichoke in which the carbohydrates were not hydrolysed prior to fermentation. The experiments revealed that this juice contains enough nutrients and can serve as a complete medium without additional nutrients both for growth of the yeasts and for ethanol production. It was found that both specific ethanol productivity and specific glucose uptake rates were the highest with K. marxianus ATCC 12708 (1.68 gg-1h-1 and 3.78 gg-1h-1 respectively). This microorganism produced an ethanol yield of 87.5% of the theoretical value in 25 hours.

Nutritional effects on the kinetics of ethanol production from glucose by Zymomonas mobilis

Changes in the nutritional media significantly affected specific glucose uptake rate (Qg), glucose utilization and ethanol production rate (Qp) of Zymomonas mobilis Z 10. Varying the yeast extract concentrations (pantothenate) between 0.15% and 1.0% in a 10% glucose system at μ=0.2 h-1, Qg values between 14.9 and 35.3 and Qp values between 7.4 and 14.6 were obtained. A concentration of 0.25% yeast extract gave highest results. High NH 4 + concentrations were detrimental to ethanol production, whereas phosphate, potassium and magnesium stimulated the catabolic activity. In the case of magnesium, glucose utilization increased from 2.8 to 92.2%. Batch and continuous cultures showed that by increasing catabolic activity, ethanol productivity can be increased irrespective of glucose concentration.

Relationship between maintenance energy requirement, mineral salts and efficiency of glucose to ethanol conversion by Zymomonas mobilis

Minimizing the usage of glucose carbon for growth and cell maintenance energy requirement, specific glucose uptake rates, specific ethanol production rates were increased 5-fold. At 0.2 hr−1 and Yg = 0.007–0.009, ethanol production rates of 7.99–8.46 g/ltr/hr, Qp values of 14.85 g/g/hr were obtained. This relationship is discussed in regard to glucose fermentation efficiency.

Kinetics of alcohol production by zymomonas mobilis at high sugar concentrations

Studies on the growth ofZ.mobilis revealed that high concentrations of glucose (10-25%) can be efficiently and rapidly converted to ethanol in batch culture. By comparison withS. carlsbergensis,Z.mobilis had specific glucose uptake rates and specific ethanol productivies several times greater than the yeast.Z.mobilis also had ethanol yields of up to 97% of a theoretical value.

THE EFFECT OF VARIED TEMPERATURE ON THE KINETICS OF METABOLISM OF GIBBERELLA FUJIKUROI IN STIRRED CULTURE.

The metabolism of Gibberclla Jujikuroi in stirred culture has been studied at varied temperatures over the range 8–40 °C. Two nitrogen-limited media were used, which differed only in the initial concentration of ammonium tartrate. Economic and rate constants have been derived at each stage of fermentation, and methods of relating these to temperature discussed. Each has been related to temperature both by a linear plot, and according to the Van"t Hoff – Arrhenius model.There was no significant difference between the results from the two media early in fermentation. During the storage and maintenance phases all specific rates were considerably lower on the more concentrated medium.The minimum temperature for growth was below 8 °C. Many parameters showed a discontinuity in the range 17–20 °C, and most optima were in the range 29–32 °C. At 38 °C growth ceased when the dry weight was about 2 mg/g of unfiltered broth, and no growth occurred at 40 °C.The contribution of nitrogen to dry weight was virtually independent of temperature. The glucose contribution tended to decrease slightly with increasing temperature over the whole range. The phosphate contribution was constant in the range 8–20 °C, and decreased greatly with increasing temperature from 20 to 36 °C. The magnesium contribution decreased markedly with increasing temperature over the whole range.Two general forms of relation between rate constants and temperature were found. One, a typical "skew" curve with "tail-off' at the lower temperatures, was obtained with the specific growth rate, the nitrogen and glucose quotients, the specific rate of glucose uptake in the maintenance phase, and the gibberellic acid productivity. The second relation showed a marked discontinuity in the range 17–20 °C, above which the increase with increasing temperature was less than at the lower temperatures. This form of curve was obtained with the phosphate, magnesium, and carbohydrate quotients, the linear growth rate, the rate of increase in mycelial dry weight, fat and carbohydrate in the storage phase, and the rate of glucose, phosphate, and magnesium uptake in the same period.