Ethanol production from fructose in continuous culture by free and flocculent cells of Zymomonas mobilis

Summary Zymomonas mobilis strain ZM4 was used for ethanol production from fructose (100 g/l) in continuous culture with a mineral (containing Ca pantothenate) or a rich (containing yeast extract) mediium. With both media high conversion yields were observed but the ethanol productivity was limited by the low biomass content of the fermentor. A new flocculent strain of Z.mobilis (ZM4F) was cultivated in a CSTR with an internal settler and showed a maximal productivity of 93 g/l.h (fructose conversion of 80%). When the fructose conversion was 96% an ethanol productivity of 85.6 g/l.h with an ethanol yield of 0.49 g/g (96% of theoretical) was observed.     

Continuous suspended cell culture of Mentha piperita in cell-recycled air-lift bioreactor

Summary A cell-recycled air-lift bioreactor was studied for its performance in cultivation of Mentha piperita cells producing essential oils. The reactor system sustained a stable operation over 30 days with the aid of a cell settler. The maximum cell concentration reached 50% packed cell volume and it occurred at the dilution rate of 0.27 day^-1. Volumetric productivity of essential oils in this system was substantially higher than that obtainable from batch culture.     

Immobilization of yeast cells on various supports for ethanol production

An immobilization technique has been developed for a packed bed fermenter which is being considered as one stage of a process for the production of fuel-grade ethanol from sugar solutions. Relatively inexpensive beech wood chips have been successfully used as the support material and relatively high cell loadings of 188 mg DW cells/g DW support have been achieved for a test system of Saccharomyces cerevisiae cultures.No washout of adsorbed cells occurs below a superficial liquid velocity of 8.9 × 10^-2 cm/s which can be increased to 9.7 × 10^-2 cm/s by including up to 1% Hercofloc solution in the reactor medium during the immobilization procedure. The immobilization procedure is practically unaffected by pH and temperature in the range 3.5 to 5.0 and 22 °C to 37 °C respectively.Typical ethanol productivity of 21.8g/l·hr has been obtained with wood-chip-adsorbed cells, which compares well with optimal values of 18 to 32g/l·hr obtained using free-suspension cultures in stirred-tank fermenters with cell recycle.     

Optimization of growth conditions for the induction of tyrosine decarboxylase inStreptococcus faecalis

Summary Growth conditions were investigated for optimal tyrosine decarboxylase (EC 4.1.1.25) activity in acetone dried cells ofStreptococcus faecalis. A growth pH of 6.0 was found optimal for enzyme induction. The enzyme was also shown to be growth-associated which indicates that continuous fermentation is preferable for optimal process productivity.     

Rapid derepression of in vitro nitrogenase activity in a Rhizobium strain which nodulates legumes and the nonlegume Parasponia

Using defined media and controlled gaseous conditions in vitro nitrogenase activity, as monitored by acetylene reduction, was detected after 16 hours of derepression. Specific activity of nitrogenase increased progressively over a period of 100 hours. The method used here utilises rapidly agitated cultures of Rhizobium strain ANU289, incubated at 28°C at cell densities of ca. 1×10⁹ cells ml^–1. The optimal medium for rapid derepression contained basic physiological salts with 3 mM glutamate and 50 mM sodium succinate being the only carbon and nitrogen additives. The gas phase was kept constant by a continuous flow of an air-nitrogen mixture with oxygen being maintained at 0.2%. The described culture system provides the opportunity to observe the regulation of nitrogenase activity in a near-chemostat situation.     

Biomass production from the green algae Chlorella vulgaris and Ankistrodesmus braunii cultured heterotrophically

Summary Ankistrodesmus braunii and Chlorella vulgaris were cultured heterotrophically under various operating conditions. The maximum rate of biomass production was 900 and 900 mg L^-1 d^-1 by C. vulgaris and 1000 and 700 mg L^-1 d^-1 by A. braunii in the light and dark, respectively. This indicates that these algae could produce in excess of 1530 dry weight tonnes ha^-1 y^-1 which is 10–20 times higher than the maximum production levels in the literature.     

A newly isolatedBacillus stearotheromophilus K1041 and its transformation by electroporation

Summary Optimal conditions for the plasmid transformation of a newly isolatedBacillus stearothermophilus K1041 by electroporation were investigated. The optimal conditions allowed a transformation efficiency of 5.8×10⁵ transformants per μg plasmid pUB110.     

Effects of organism type and growth conditions on cell disruption by impingement

Data for disruption of C. utilis, S. cerevisiae and B. subtilis cells by impingement of a high velocity jet of suspended cells against a stationary surface are compared. Differences between organisms were observed, but there were no general differences found between yeast and bacteria. In addition, growth conditions were found to have an effect on disruption with cells grown at a high specific growth rate easier to disrupt than cells grown at a low rate.Nomenclature a exponent of pressure (dimensionless) - D dilution rate (h^\s-1) - K dimensional rate constant (Pa ^\s-) - N number of passes (dimensionless) - P operating pressure (Pa) - R fraction of cells disrupted (dimensionless) - u_m maximum specific growth rate (h^\s-1)     

The effect of pH,temperature and sucrose concentration on high productivity continuous ethanol fermentation using Zymomonas mobilis

Summary A flocculent strain of Zymomonas mobilis was used for ethanol production from sucrose. Using a fermentor with cell recycle (internal and external settler) high sugar conversion and ethanol productivity were obtained. At a dilution rate of 0.5 h^-1 (giving 96% sugar conversion) the ethanol productivity, yield and concentrations respectively were 20 g/l/h, 0.45 g/g and 40 g/l using a medium containing 100 g/l sucrose. At a sucrose concentration of 150 g/l, the ethanol concentration reached 60 g/l. The ethanol yield was 80% theoretical due to levan and fructo-oligomer formation. No sorbitol was detected. This fermentation was conducted at a range of conditions from 30 to 36°C and from pH 4.0 to 5.5.     

Diacetyl production by co-immobilized citrate-positiveLactococcus lactis subsp.lactis 3022 and homogenized bovin liver in alginate fibers with double gel layers

Summary Diacetyl production by (Citr⁺)Lactococcus lactis subsp.lactis 3022 cells immobilized in Ca-alginate fine fibers with single layer in the presence of catalase was three times higher than that in the absence of catalase. A co-immobilized culture system of the lactic acid bacterial cells (outer) and the homogenized bovine liver (inner layer) in Ca-alginate fibers with double gel layers was developed. The culture system gave high diacetyl productivity (30 mg/l) for ten repeated batch cultures.     

Production of l-glutamate by immobilized protoplasts

Summary Protoplasts of Brevibacterium flavum cultured in a medium containing 50 g·l^-1 of biotin were prepared with lysozyme and immobilized in matrices of agar-acetylcellulose filters. The immobilized protoplasts were applied to l-glutamate production from glucose and urea in a batch system. The productivity of l-glutamate by the immobilized protoplasts was 2.5 times higher than that by immobilized whole cells under optimal conditions. Maximal productivity initially reached 1.5 mg·ml^-1. The immobilized protoplasts of B. flavum could be used six times for l-glutamate production with retention of about 70% of the initial productivity.     

The kinetics of glucose fermentation bySelenomonas ruminantium HD4 grown in continuous culture

Summary The production of organic acids (acetate, lactate, and propionate) by the anaerobic, ruminal bacteriumSelenomonas ruminantium HD4 was investigated in both glucose-limited and glucose-sufficient (phosphate-limited) continuous cultures. The fermentation pattern of products exhibited a shift upon release of glucose limitation from acetate and propionate to lactate at a dilution rate of 0.2 h^–1. Glucose sufficiency brought about two-to fourfold increase in specific glucose utilization rate, lactate productivity, and lactate yield relative to glucose-limited growth conditions. The increased lactate production under glucose-sufficient growth conditions was attributed to the overutilization of excess glucose.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Glycolate excretion by Rhodospirillum rubrum

Glycolate can be measured in the supernatant fraction after incubation of butyrate-grown cells of Rhodospirillum rubrum either colorimetrically by the Calkins method or enzymatically using glycolate oxidase. Under optimal conditions, half-maximal excretion occurs at 11% O₂ and the maximal rate is 6.9 nmol of glycolate min^-1 mg protein^-1 at 30°C. The pH and temperature optima are 7.6 and 30°C and light intensity is saturating in the range of 2–10×10⁴ lux. Carbon dioxide inhibits glycolate excretion and exogenous butyrate stimulates. Glycolate excretion is maximal by butyrate-light grown cells harvested in the early stationary phase and under all conditions is proportional to the cellular content of ribulose 1,5-bisphosphate carboxylase/oxygenase.Non-Standard Abbreviations Bicine (N,N-bis[2-hydroxyethyl]glycine) - RuBP d-ribulose-1,5-bisphosphate - HPMS 2-pyridylhydroxymethanesulfonate     

Ethanol production with Saccharomyces cerevisiae at potassium-limited aerobic growth conditions

Summary The specific ethanol productivity withSaccharomyces cerevisiae grown aerobically in a chemostat at a growth rate of 0.17 hr^–1 was found to increase from zero to 13 mmol/g cell dry matter·h when the potassium content in the substrate used was decreased to 0.05 mol/kg glucose. 78% of the glucose metabolized were converted to ethanol under these aerobic growth conditions.     

Increase of hyaluronate lyase productivity by repeated batch fermentation

Summary The production of hyaluronate lyase (E.C.4.2.2.1.), HL, byStreptococcus equisimilis strain SHL-03 has been studied under repeated batch culture conditions with fixed harvest volume (discharged fraction, =0.875). The productivity of this system was 49.2% higher than that of a classical batch culture. The process could be repeated at least for 15 cycles (245 hours) with a productivity of 33.77 U/ml h and a yield of 12,800-U/g Glu.These results suggest that this system could provide a useful procedure to increase the productivity of HL production.     

Kinetics of ethanol production by yeast in continuous culture

Summary The rate of fermentation of glucose by Saccharomyces uvarum in steadystate continuous culture in excess of substrates showed non-competitive inhibition kinetics with respect to ethanol. A model is presented which predicts that growth stops at a finite ethanol concentration, which was calculated to be 95 gl^-1 for the system used here. The observed maximum ethanol concentration in a single stage continuous culture was 92 gl^-1.     

Performance of Chlorella sorokiniana under simulated extreme winter conditions

High annual microalgae productivities can only be achieved if solar light is efficiently used through the different seasons. During winter the productivity is low because of the light and temperature conditions. The productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed under the worst-case scenario found during winter time in Huelva, south of Spain. The maximum light intensity (800?μmol photons m^-2 s^-1) and temperature (20°C) during winter were simulated in a lab-scale photobioreactor with a short light-path of 14?mm. Chemostat conditions were applied and the results were compared with a temperature-controlled situation at 38°C (optimal growth temperature for C. sorokiniana). When temperature was optimal the highest productivity was found at a dilution rate of 0.18 h^-1 (P _v?=?0.28?g Kg^-1 h^-1), and the biomass yield on light energy was high (Y _x,E?=?1.2?g?mol^-1 photons supplied). However, at suboptimal temperature, the specific growth rate of C. sorokiniana was surprisingly low, not being able to support continuous operation at a dilution rate higher than 0.02 h^-1. The slow metabolism under suboptimal temperature resulted in a decline of the light energy requirements of the cells. Consequently, the maximum winter irradiance was experienced as excessive, leading to a low photosynthetic efficiency and productivity (Y _x,E?=?0.5?g mol^-1 photons supplied, P _v?=?0.1?g Kg^-1 h^-1). At suboptimal temperature a higher carotenoid-to-chlorophyll ratio was observed indicating the activation of light-dissipating processes. We conclude that temperature control and/or light dilution during winter time will enhance the productivity.     

Formaldehyde Production by Cells of a Mutant of Candida boidinii S2 Grown in Methanol-limited Chemostat Culture

Formaldehyde production was investigated with cells of a mutant, AOU-1, of a methanol yeast, Candida boidinii S2 grown in methanol-limited chemostat culture. The highest productivity was shown with cells from the culture at a dilution rate of 0.075 hr^-1, when cells had the highest activity of alcohol oxidase and almost minimum activity of formaldehyde dehydrogenase. Under optimal reaction conditions, 950 mm formaldehyde was produced in 10-hr reaction with the cells. By the chemostat culture, not only formaldehyde productivity but also cell productivity was improved in comparison with batch culture. A maximum cell productivity of 0.2 g · liter^-1 · hr^-1 and a cell yield of 47% were obtained.     

Lactase production in continuous culture by Trichoderma reesei Rut-C30

Summary Trichoderma reesei Rut-C30 was found to produce extracellular lactase when grown on lactose medium. Maximum enzyme levels in continuous culture were observed at dilution rates (D) between 0.02 and 0.027 hr^-1. The enzyme productivity reached 27.3 U/L hr at D = 0.027 hr^-1. Lactase synthesis appears to be inducible and subject to catabolite repression. Optimal growth temperature and pH for enzyme production were 28°C and pH 5. Maximum enzyme activity was observed at 63°C and pH 4.6. The apparent K_m, based on the nitrophenyl-galactopyranoside assay was estimated as 0.4 mM. The enzyme is suitable for lactose hydrolysis in acid whey.     

Activation of tubulinyl-tyrosine carboxypeptidase by spermine,spermidine and putrescine

Spermine, spermidine and putrescine produce dose dependent stimulation of the invitro tubulinyl-tyrosine carboxypeptidase. Maximal stimulation was obtained with spermine, spermidine or putrescine at 0.06 mM, 1 mM and 6 mM, respectively. At higher concentrations, the enzyme activity was inhibited. The enzyme was also activated by Mg⁺⁺; the concentration formaximal effect was 4–6 mM. The stimulation produced by optimal concentration of each amine was unaffected by Mg⁺⁺ up to 2 mM; higher concentration of Mg⁺⁺ showed inhibitory effect. At optimal Mg⁺⁺ concentration, the carboxypeptidase activity was inhibited by increasing amine concentration. The amines at 0.5 or 5 mM did not produce any effect on the incorporation of tyrosine catalyzed by tubulin tyrosine ligase.