Ethanol production by yeast cells immobilized in open-pore agar

An open-pore agar matrix has been shown to be suitable for the entrapment of microbial whole cells required for use in reactions that involve cell growth and gas evolution. Beads of porous agar with entrapped yeast cells have been used for the continuous fermentation of sugar cane molasses to ethanol, without apparent bead rupture, even after periods of 3 mo of use. The agar gel does not erode during prolonged operation, unlike porous gelatin cross-linked with glutaraldehyde.     

Real-time detection of cofactor availability in genetically modified living Saccharomyces cerevisiae cells — Simultaneous probing of different geno- and phenotypes

This work describes a mediated amperometric method for simultaneous real-time probing of the NAD(P)H availability in two different phenotypes, fermentative and respiratory, of the phosphoglucose isomerase deletion mutant strain of S. cerevisiae, EBY44 [ENY.WA-1A pgi1-1D::URA3], and its parental strain, ENY.WA-1A. The developed method is based on multichannel detection using microelectrode arrays. Its versatility was demonstrated by using four microelectrode arrays for simultaneously monitoring the NAD(P)H availability of both geno- and phenotypes under the influence of two different carbon sources, glucose and fructose, as well as the cytosolic and mitochondrial inhibitor and uncoupler, dicoumarol. The obtained results indicate that the method is capable of accurately and reproducibly (overall relative standard error of mean 3.2%) mapping the real-time responses of the cells with different genotype–phenotype combinations. The ENY.WA cells showed the same response to glucose and fructose when dicoumarol was used; fermentative cells indicated the presence of cytosolic inhibition and respiratory cells a net effect of mitochondrial uncoupling. EBY44 cells showed cytosolic inhibition with the exception of respiratory cells when fructose was used as carbon source.     

Hybrid process for the conversion of lignocellulosic materials

Because of the recalcitrant nature of lignocellulosic materials, it is important to pretreat the biomass in order to obtain a suitable material for the bioconversion. In this study, two different types of pretreatments were performed. The first experiment used a 2-gal Parr reactor operated at 140, 150,160, and 170‡C with sulfuric acid concentrations varying from 0.5 to 2%. A second pretreatment was performed with a two-stage low-temperature process. The first-stage pretreatment was performed at 100 or 120‡C with sulfuric acid concentrations of 0.5, 2, and 5% followed by a secondstage pretreatment at 120‡C with 2% acid concentration. The best residues for enzymatic hydrolysis and simultaneous saccharification and fermentations (SSF) came from the higher temperature pretreatment with the Parr reactor. However, a large portion of the xylose fraction was degraded to furfural and glucose was degraded to HMF. On the contrary, the two-stage low temperature pretreatment resulted in a very low percentage of xylose degradation, and no glucose degradation. The residues from this two-stage pretreatment performed satisfactorily toward the production of ethanol by SSFs. This study discusses the results obtained from these experiments.     

氧和葡萄糖对啤酒酵母细胞核基因pet54表达调控的研究

为研究氧和葡萄糖对ｐｅｔ５４基因表达的调控，构建了ｐｅｔ５４：：ｌａｃＺ融合基因，用于监测有呼吸的二倍体菌株中ｐｅｔ５４基因的表达．实验结果表明氧促进ＰＥＴ５４基因表达，葡萄糖阻遏ｐｅｔ５４基因表达．     

Characterization of an immobilized yeast cells fluidized-bed bioreactor for ethanol fermentation

The operational characterization of a fluidized-bed bioreactor for ethanol fermentation using Ca-alginate immobilized yeast cells is described. An additional air stream is supplied to the fermenter to ensure and maintain satisfactory fluidization behavior of beads and to avoid slug formation. The influence of physical properties such as bead density and liquid density on the fluidization quality and stability are discussed.     

The functional relationship between Baker’s yeast intracellular lysine and aeration rate and sodium chloride

The results of this study confirm the enhanced production of L-lysine bySaccharomyces cerevisiae during the fermentation of glucose at a 0.6M concentration of NaCl previously observed (8). Changes in NaCl concentration above or below 0.6M caused a drop in the maximum production of lysine. Fermentations run at 1.0, 1.4, and 1.8 VVM aeration rates and at 0.0, 0.3, 0.6, 0.9, and 1.2M NaCl concentrations gave the highest intracellular lysine yield at 0.6M and 1.4 VVM.     

Catabolic capacity of Saccharomyces cerevisiae in relation to the physiological state and maintenance requirement

The importance of the physiological state for the catabolic capacity during carbon- and energy-starving conditions was studied. Endogenous metabolism was low in cells depleted of carbon and energy source. This does not necessarily mean that these cells do not have the capacity for a higher catabolic activity. To measure the catabolic capacity of starved cells, carbon- and energy-depleted cells were suspended in synthetic fresh water and the respiratory and fermentative rates were examined after addition of glucose. The catabolic capacity was studied in cells of different physiological states. Stationary phase cells, which were depleted of their carbon and energy source for 6 h, showed a lower respiratory capacity, but almost as high a fermentative capacity as cells originating from the logarithmic phase of growth on glucose. With extended starvation time of stationary phase cells, the fermentative capacity decreased, while the respiratory capacity increased. Transition phase cells, characterised by a metabolic shift from a mixed respiratory-fermentative catabolism to a purely respiratory catabolism, showed, when newly harvested, a lower fermentative capacity than log phase cells with a mixed respiratory-fermentative catabolism. However, the fermentative capacity decreased during starvation of carbon and energy source for log phase cells, whereas transition phase cells increased the fermentative capacity to the same level as that of newly harvested log phase cells after 4 days without carbon or energy source.

The addition of glucose to stationary phase cells under non-growth conditions (no nitrogen source) resulted in ATP production rates of between 50% and almost 100% of the ATP produced by newly harvested log phase cells under the same conditions. Much higher rates of ATP production were attained for these different types of physiological states than can be explained by maintenance energy requirements. The suggested explanation for this over-consumption of energy during non-growth conditions in response to energy excess is metabolic uncoupling. This behaviour is discussed in relation to maintenance energy requirements during different environmental conditions.     

Biomethylation of tin (II) complexes in the presence of pure strains of Saccharomyces cerevisiae

The methylation of several tin compounds by strains of Saccharomyces cerevisiae strains (yeast) is described. The production of the methyl tin species was established by gas chromatography and mass spectrometry. Monomethyl tin (IV) products dominated but some dimethyl tin products were observed. This appears to be the first report of a tin methylation by a pure strain of a methylating species rather than a complex mixture obtained from an environmental source.     

Baker’s yeast (Saccharomyces cerevisiae) mediated transformations of C-aryl-N-phenylnitrones

C-Aryl-N-phenylnitrones are transformed to a mixture of azoxybenzene and aryl aldehydes when treated with a mixture of Baker’s yeast and sucrose in pH = 6.0 phosphate buffer medium at 32 °C.     

Production of single cell protein (SCP) from food and agricultural waste by using Saccharomyces cerevisiae

Food waste is the single-largest component of the waste stream, in order to protect and safeguard the public health, useful and innovative recycling methods are investigated. The conversion of food wastes in value-added products is becoming a more economically viable and interesting practice. Food waste, collected in the distribution sector and citrus industries, was characterised for its potential as a raw material to use in fermentation processes. In this study, the production of single-cell protein (SCP) using food waste as a substrate was investigated. The purpose of this study has been to produce SCP from mixtures of food waste using Saccharomyces cerevisiae. The main fermentation test was carried out using a 25 l bioreactor. The utilisation of food waste can allow us to not only to reduce environmental pollution, but also to obtain value-added products such as protein supply for animal feed.