Conversion efficiency of glucose/xylose mixtures for ethanol production using Saccharomyces cerevisiae ITV01 and Pichia stipitis NRRL Y‐7124

BACKGROUND: Efficient conversion of glucose/xylose mixtures from lignocellulose is necessary for commercially viable ethanol production. Oxygen and carbon sources are of paramount importance for ethanol yield. The aim of this work was to evaluate different glucose/xylose mixtures for ethanol production using S. cerevisiae ITV‐01 (wild type yeast) and P. stipitis NRRL Y‐7124 and the effect of supplying oxygen in separate and co‐culture processes. RESULTS: The complete conversion of a glucose/xylose mixture (75/30 g L^?1) was obtained using P. stipitis NRRL Y‐7124 under aerobic conditions (0.6 vvm), the highest yield production being Y_p/s = 0.46 g g^?1, volumetric ethanol productivity Q_pmax = 0.24 g L^?1 h^?1 and maximum ethanol concentration P_max = 34.5 g L^?1. In the co‐culture process and under aerobic conditions, incomplete conversion of glucose/xylose mixture was observed (20.4% residual xylose), with a maximum ethanol production of 30.3 g L^?1, ethanol yield of 0.4 g g^?1 and Q_pmax = 1.26 g L^?1 h^?1. CONCLUSIONS: The oxygen present in the glucose/xylose mixture promotes complete sugar consumption by P. stipitis NRRL Y‐7124 resulting in ethanol production. However, in co‐culture with S. cerevisiae ITV‐01 under aerobic conditions, incomplete fermentation occurs that could be caused by oxygen limitation and ethanol inhibition by P. stipitis NRRL Y‐7124; nevertheless the volumetric ethanol productivity increases fivefold compared with separate culture. Copyright © 2011 Society of Chemical Industry     

Improvement of ethanol production in Saccharomyces cerevisiae by hetero‐expression of GAPN and FPS1 deletion

BACKGROUND: During anaerobic bioethanol fermentation of Saccharomyces cerevisiae, the main byproduct glycerol is essential to regulate redox balance (reoxidize NADH to NAD⁺), which is necessary to maintain cell growth and fermentation. Hetero‐expression of a NADP⁺‐dependent glyceraldehydes‐3‐phosphate dehydrogenase (GAPN) [EC.1.2.1.9] in S. cerevisiae could redirect the carbon flux from glycerol to ethanol involving a net oxidation of NADH. The present study investigates whether combination of GAPN hetero‐expression and glycerol exporter Fps1p disruption would result in less glycerol and more ethanol production without affecting growth rate during anaerobic fermentations. RESULTS: The results of anaerobic fermentations showed that the fps1Δ mutant with GAPN (named 4FG) produced 21.47% less glycerol and 9.18% more ethanol compared with a parental strain with a control plasmid, while the rates of growth and fermentation were not changed. Moreover, the engineered strain 4FG yielded less glycerol and acetic acid, and more ethanol than the control, fps1Δ mutant or with GAPN only. CONCLUSIONS: During anaerobic fermentations, hetero‐expression of GAPN restored the reduced grow rate of the fps1Δ mutant, and led to less byproducts and more ethanol production. This combination strategy could be used to modulate glycerol metabolism and optimize the anaerobic fermentation of S. cerevisiae. Copyright © 2011 Society of Chemical Industry     

Co‐culture of Penicillium chrysogenum and Saccharomyces cerevisiae leading to the immobilization of yeast

BACKGROUND: Under appropriate conditions, Saccharomyces cerevisiae and Penicillium chrysogenum were found to co‐immobilize spontaneously with no need for external support or chemical binder. The main aims were to examine the interaction between yeast cells and fungal hyphae by electron microscopy and the death of the filamentous fungus because of direct contact between both microorganisms. RESULTS: Immobilization was accomplished by orbitally shaking at 28 °C a culture medium consisting of yeast nitrogen base buffered at pH 7 and containing gluconic acid as an available carbon source for the filamentous fungus not readily used by the yeast. The yeast biocapsules thus obtained were hollow, smooth, elastic, strong, creamy‐coloured spheres of variable size depending on the particular shaking rate and time of residence in the formation medium. Biocapsule walls consisted of yeast cells bound to fungal hyphae. Placing the biocapsules in fermentation medium caused yeast cells to colonize and invade all hyphae, thereby causing the fungus to die and remain as a mere support for yeast. CONCLUSIONS: The death of the fungus was probably effected by the yeast via a cell‐hypha contact‐mediated mechanism as shown by dialysis experiments. The yeast biocapsules can be reused with no loss of integrity or activity. The proposed immobilization method provides a simple, convenient, inexpensive alternative which affords yeast reuse. Copyright © 2011 Society of Chemical Industry     

Productivity enhancement of S‐adenosylmethionine in Saccharomyces cerevisiae using n‐hexadecane as oxygen vector

BACKGROUND: Saccharomyces cerevisiae is one of the main microorganisms that can produce S‐adenosylmethionine (SAM) from L‐methionine and ATP with high productivity. To satisfy the ATP requirement for SAM synthesis, sufficient oxygen should be supplied to the medium to improve aerobic metabolism in S. cerevisiae. In this study, n‐hexadecane used as oxygen vector for enhancement of SAM production by this yeast was investigated. RESULTS: N‐hexadecane was most favorable for cell growth and SAM synthesis in S. cerevisiae when added at the time of inoculation. It could increase glucose consumption, reduce ethanol accumulation, and ultimately improve biomass and SAM productivity in a fermentation process. In a bioreactor, the highest yield of SAM (2.27 g L^?1) was achieved in the presence of 4% (v/v) n‐hexadecane after 24 h of inoculation, which was 23.37% higher than the control (1.84 g L^?1). CONCLUSION: The addition of n‐hexadecane to cultures of S. cerevisiae significantly enhanced SAM production without increasing energy consumption, and has the potential for use in large‐scale fermentation processes to increase oxygen supply. Copyright © 2012 Society of Chemical Industry     

Effects of light wavelength and intensity on the production of ethanol by Saccharomyces cerevisiae in batch cultures

BACKGROUND: Photoreceptors have been identified in Saccharomyces cerevisae, however, the influence of light on the performance of ethanol fermentation of S. cerevisiae is not yet clear. The aims of this study are to elucidate the influence of light wavelength and intensity on the growth and ethanol production of S. cerevisiae and to describe a novel two‐stage LED light process to optimize ethanol fermentation. RESULTS: Experimental results indicated that maximum biomass concentration X_max of the batch under red LED light increased monotonically with light intensity, and the optimal specific product yield Y_p/x was 13.2 g g^?1 at 600 lux. Maximum ethanol concentration P_max of the batch under blue LED light increased monotonically with light intensity, and the optimal Y_p/x was 18.4 g g^?1 at 900 lux. A novel two‐stage LED light process achieved maximum P_max, of 98.7 g dm^?3 resulting in 36% improvement compared with that of the batch in the dark. CONCLUSION: The light wavelength and its intensity significantly affected cell growth and ethanol formation of S. cerevisiae. Red LED light (630 nm) stimulated cell growth but slightly inhibited ethanol formation. In contrast, blue LED light (470 nm) significantly inhibited cell growth but stimulated ethanol formation. A novel two‐stage LED light process has been successfully demonstrated to optimize ethanol fermentation of S. cerevisiae. Copyright © 2009 Society of Chemical Industry     

Effect of different fermentation parameters on bioethanol production from corn meal hydrolyzates by free and immobilized cells of Saccharomyces cerevisiae var. ellipsoideus

BACKGROUND: Bioethanol produced from renewable biomass, such as corn meal, is a biofuel that is both renewable and environmentally friendly. Significant scientific and technological investments will be needed to achieve substitution of conventional fossil fuels with alternative fuels. The ethanol fermentation of enzymatically obtained corn meal hydrolyzates by free and immobilized cells of Saccharomyces cerevisiae var. ellipsoideus yeast in a batch system was studied. The initial glucose and inoculum concentration and the time required for the efficient ethanol production were optimized taking into account parameters such as ethanol concentration, ethanol yield, percentage of the theoretical yield of ethanol and volumetric productivity in both immobilized and free cell systems. RESULTS: The yeast cells were immobilized in Ca–alginate by an electrostatic droplet generation method. An optimal initial inoculum concentration of 2% (v/v) and optimal fermentation time of 38 h for both immobilized and free yeasts were determined. An optimal initial glucose concentration of 150 g L^?1 for free system was achieved. At the initial glucose concentration of 176 g L no substrate or product inhibition were achieved with immobilized yeast. CONCLUSION: By immobilization of the yeast into Ca–alginate using the method of electrostatic droplet generation a superior system was realized, which exhibited lower substrate inhibition and higher tolerance to ethanol. The cells of S. cerevisiae var. ellipsoideus yeast entrapped in Ca–alginate showed good physical and chemical stability, and no substrate and product diffusion restrictions were noticed. Copyright © 2008 Society of Chemical Industry     

Kinetic study on cross‐linking and blowing behavior of EVA/EPDM/CPE high elasticity material

Blend of ethylene‐vinyl acetate copolymer (EVA), ethylene‐propylene‐diene terpolymer rubber (EPDM), and chlorinated polyethylene (CPE) filled with talc was cross‐linked with dicumyl peroxide and blown simultaneously with azodicarbonamide for preparation of high elasticity material by injecting, cross‐linking, and blowing process. It had excellent mechanical properties and elasticity. It was found that mechanical properties were a function of cross‐linking and blowing temperature and time and formula. A good cross‐linking and blowing temperature was in the range of 440–450 K and the optimum temperature and time were 448 K and 360 s, respectively. Kinetics of both cross‐linking and blowing reactions were investigated by closed nonrotor torque rheometer. The results showed that both cross‐linking and blowing reactions were first order. The activation energy of the cross‐linking reaction was higher than that of the blowing reaction. With increasing of EDPM content, the activation energy of the cross‐linking reaction reduced whereas it increased for the blowing reaction. The gas cell morphology was characterized by scanning electron microscopy (SEM). The results of SEM and mechanical property analyses showed that the morphology and mechanical properties were improved by incorporating CPE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

A thermal study on the use of immobilized penicillin G acylase in the formation of 7‐amino‐3‐deacetoxy cephalosporanic acid from cephalosporin G

Penicillin G acylase (PGA) is an important enzyme for the industrial production of 7‐amino‐3‐deacetoxy cephalosporanic acid (7‐ADCA) from cephalosporin G (Ceph‐G), and 6‐aminopenicillanic acid (6‐APA) from penicillin G (Pen‐G). These products are used for the manufacture of semi‐synthetic cephalosporins and penicillins. In this study, immobilized PGA was utilized to catalyze the conversion of Ceph‐G to 7‐ADCA. The optimal conditions were found to be an operating temperature of 45 °C, 0.2 M phosphate buffer, a substrate concentration of 30 mg cm^?3 and a catalyst particle concentration of 0.01 g cm^?3 (specific activity of 623.2 U g^?1). Up to 45 °C the reaction was characterized by an activation energy of 38.66 kJ mol^?1. Beyond 57.5 °C there was a sharp decline of activity, characterized by a deactivation energy of 235.88 kJ mol^?1. Copyright © 2004 Society of Chemical Industry