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In this study, major factors involved in regulating ethanol production from wood by the saprotrophic white-rot fungus Phanerochaete sordida YK-624 were investigated. P. sordida YK-624 produced ethanol from wood meal culture without the addition of any nutrients, and ethanol was produced from wood culture only when the oxygen concentration in headspace was reduced to ≤5%; thereafter, ethanol production ceased within a few days. Analyses of gene expression during aerobic incubation indicated that P. sordida simultaneously upregulates the glycolytic pathway from sugar uptake to pyruvate conversion during ethanol fermentation and suppresses pyruvate influx into the TCA cycle. Upon termination of ethanol fermentation, the expression of all tested genes was repressed, and the fungus ceased to grow. In contrast, the fungus could utilize ethanol for aerobic growth. These results suggest that ethanol fermentation by P. sordida functions as a short-term stress response system under anaerobic conditions during wood decay, enabling the fungus to rapidly resume growing when oxygen is supplied (e.g., following breakdown of plant cell walls or removal of the fungus from water immersion). This is the first report to describe the physiologic significance of ethanol fermentation in saprotrophic white-rot fungi. [Display omitted] • The biological significance of ethanol fermentation by saprotrophic white-rot fungus P. sordida YK-624 was speculated. • P. sordida YK-624 produced ethanol from wood meal without addition of any nutrients under hypoxic condition. • P. sordida YK-624 could survive and ferment for only a few days under hypoxia conditions during wood decay. • Ethanol fermentation in P. sordida YK-624 appears to be a short-term hypoxia tolerance system. [ABSTRACT FROM AUTHOR]

One of the key processes in making beer is fermentation. In the fermentation process, brewer's yeast plays an essential role in both the production of ethanol and the flavor profile of beer. Therefore, the mechanism of ethanol fermentation by of brewer's yeast is attracting much attention. The high ethanol productivity of sake yeast has provided a good basis from which to investigate the factors that regulate the fermentation rates of brewer's yeast. Recent studies found that the elevated fermentation rate of sake Saccharomyces cerevisiae species is closely related to a defective transition from vegetative growth to the quiescent (G 0 ) state. In the present study, to clarify the relationship between the fermentation rate of brewer's yeast and entry into G 0 , we constructed two types of mutant of the bottom-fermenting brewer's yeast Saccharomyces pastorianus Weihenstephan 34/70: a RIM15 gene disruptant that was defective in entry into G 0 ; and a CLN3 Δ PEST mutant, in which the G 1 cyclin Cln3p accumulated at high levels. Both strains exhibited higher fermentation rates under high-maltose medium or high-gravity wort conditions (20° Plato) as compared with the wild-type strain. Furthermore, G 1 arrest and/or G 0 entry were defective in both the RIM15 disruptant and the CLN3 Δ PEST mutant as compared with the wild-type strain. Taken together, these results indicate that regulation of the G 0 /G 1 transition might govern the fermentation rate of bottom-fermenting brewer's yeast in high-gravity wort. [ABSTRACT FROM AUTHOR]

Laser radiation is an efficient approach for rapid improvement of industrial microbial phenotypes. To improve ethanol tolerance in Saccharomyces cerevisiae strains, a 266 nm laser radiation with the use of repetitive cultivation was explored in this work. After irradiated by 266 nm laser radiation and repetitive cultivation, a genetically stable SM4 strain was obtained. The SM4 strain could grow on YPD plate with extra 15% (v/v) ethanol. Moreover, the ethanol production performance of SM4 strain was 29.25% more than that of the wild type strain when they were cultivated in 5% (v/v) ethanol fermentation medium for 72 h. The DNA mutation was the possible characters for the phenotype of SM4 strain. Overall, the 266 nm laser radiation and repetitive cultivation approach might be a novel and useful for breeding fermentation microorganisms. [ABSTRACT FROM AUTHOR]

In this work we conducted the pseudo-continuous fermentation, i.e., continuous fermentation with cell retention, using Scheffersomyces stipitis, and studied its effect on ethanol tolerance of the strain. During the fermentation experiments, S. stipitis was adapted to a mild concentration of ethanol (20–26 g/L) for two weeks. Two substrates (glucose and xylose) were used in different fermentation experiments. After fermentation, various experiments were performed to evaluate the ethanol tolerance of adapted cells and unadapted cells. Compared to the unadapted cells, the viability of adapted cells increased by 8 folds with glucose as the carbon source and 6 folds with xylose as the carbon source following exposure to 60 g/L ethanol for 2 h. Improved ethanol tolerance of the adapted cells was also revealed in the effects of ethanol on plasma membrane permeability, extracellular alkalization and acidification. The mathematical modeling of cell leakage, extracellular alkalization and acidification revealed that cells cultured on glucose show better ethanol tolerance than cells cultured on xylose but the differences become smaller for adapted cells. The results show that pseudo-continuous fermentation can effectively improve cell's ethanol tolerance due to the environmental pressure during the fermentation process. [ABSTRACT FROM AUTHOR]

Ethanol fermentation from food wastes containing mainly starch without carrying out sterilization was investigated by using wild and tolerant yeast, Issatchenkia orientalis MF-121. The MF-121 strain is not a suitable choice for ethanol fermentation from lignocellulosic biomass because it is only capable of fermenting hexoses of glucose, mannose, and fructose to ethanol. Therefore, we first isolated acid- and salt-tolerant yeast that are capable of fermenting various monosaccharides to ethanol, and the isolated yeast that showed the ability to ferment ethanol from glucose, mannose, galactose, fructose, and xylose, was identified as Zygoascus hellenicus LK-5G on the basis of the 26S rRNA sequence analysis. [Copyright &y& Elsevier]

We previously reported the construction of a recombinant Candida utilis strain expressing mXYL1, XYL2 and XYL3, which encode mutated Candida shehatae xylose reductase K275R/N277D, C. shehatae xylitol dehydrogenase and Pichia stipitis xylulokinase to produce ethanol from xylose. However, its productivity was low. In this study, to breed a strain with higher productivity of ethanol from xylose, we used a cocktail multicopy integration method to attain optimized gene dosage of the three enzymes. Gene expression cassettes of the xylose-metabolizing enzymes were simultaneously integrated into C. utilis chromosomes in one step. Measurement of integrated gene copy number and xylose fermentability in all of the resulting integrant strains revealed that the copy number ratio of XYL2/mXYL1 in strains with higher ethanol yield was higher than that in strains with lower ethanol yield, whereas the copy number ratio of mXYL1/XYL3 was lower in strains with higher ethanol yield. The resultant strain CIS35, which was found to be the best producer of ethanol from xylose produced 29.2 g/L of ethanol, yielding 0.402 g ethanol/g xylose. This result provides that C. utilis may be a good candidate as a host for ethanol production from xylose. [Copyright &y& Elsevier]

Abstract: Cellular and subcellular morphology reflects the physiological state of a cell. To determine the physiological nature of sake yeast with superior fermentation properties, we quantitatively analyzed the morphology of sake yeast cells by using the CalMorph system. All the sake strains examined here exhibited common morphological traits that are typically observed in the well-characterized whiskey (whi) mutants that show accelerated G1/S transition. In agreement with this finding, the sake strain showed less efficient G0/G1 arrest and elevated expression of the G1 cyclin gene CLN3 throughout the fermentation period. Furthermore, deletion of CLN3 remarkably impaired the fermentation rate in both sake and laboratory strains. Disruption of the SWI6 gene, a transcriptional coactivator responsible for Cln3p-mediated G1/S transition, also resulted in a decreased fermentation rate, whereas whi mutants exhibited significant improvement in the fermentation rate, demonstrating positive roles of Cln3p and its downstream signalling pathway in facilitating ethanol fermentation. The combined results indicate that enhanced induction of CLN3 contributes to the high fermentation rate of sake yeast, which are natural whi mutants. [Copyright &y& Elsevier]

In small-scale sake brewing tests, progression of ethanol fermentation is examined by monitoring carbon dioxide emission using the Fermograph, an automated multi-channel gas monitor instrument. The Fermograph system enables automatic measurements of fermentation profiles with high accuracy, reproducibility, and resolution, and facilitates comprehensive and quantitative sake fermentation kinetic analyses. [ABSTRACT FROM AUTHOR]

Abstract: Respiration-deficient mutant (RDM) strains of Zymomonas mobilis were isolated from antibiotic-resistant mutants. These RDM strains showed various degrees of respiratory deficiency. All RDM strains exhibited much higher ethanol fermentation capacity than the wild-type strain under aerobic conditions. The strains also gained thermotolerance and exhibited greater ethanol production at high temperature (39°C), under both non-aerobic and aerobic conditions, compared with the wild-type strain. Microarray and subsequent quantitative PCR analyses suggest that enhanced gene expression involved in the metabolism of glucose to ethanol resulted in the high ethanol production of RDM strains under aerobic growth conditions. Reduction of intracellular oxidative stress may also result in improved ethanol fermentation by RDM strains at high temperatures. [Copyright &y& Elsevier]

Four kinds of transporters, HXT1 and HXY7 from Saccharomyces cerevisiae, and GXF1 and GXS1 from Candida intermedia, were overexpressed in xylose-metabolizing S. cerevisiae harboring a xyloseisomerase-based pathway. Overexpression of transporter enhanced sugar consumption and ethanol production, and GXF1 was efficient for ethanol fermentation from both glucose and xylose. [ABSTRACT FROM AUTHOR]

Abstract: Ethanol-producing Escherichia coli strain KO11 consumed 99% of the glucose and only 13% of the xylose in a mixture of glucose (60g/L) and xylose (40g/L) during the 72-h fermentation at 30°C. The deletion mutants ΔptsG, ΔmanXYZ, and ΔptsG/manXYZ utilized 42%, 78%, and 35% of the glucose and 50%, 32%, and 32% of the xylose, respectively. [Copyright &y& Elsevier]

Abstract: The ability of 13 strains of multi-stress-tolerant Issatchenkia orientalis yeast to produce ethanol was examined under different stress conditions, including conditions of elevated H2SO4 and Na2SO4 concentrations and increased heat. The MF-121 strain produced a significant amount of ethanol after the incubation in acidic media containing high concentrations of salt, e.g., 50g/l Na2SO4 at pH 2.0, or at high temperatures, e.g., 43°C, when compared with other strains. [Copyright &y& Elsevier]