Aims: Oil palm trunk (OPT) can be a potential biomass from replanting activities for biomass-to-liquid (BTL) particularly in bioethanol production. The OPT contains higher carbohydrates compared to other oil palm biomass, thus has better advantages as feedstock for biofuel. To realise this, the feasibility of using oil palm trunk (OPT) sap as a substrate for bioethanol fermentation was explored via optimising the various culture conditions (pH, temperature, inoculum size, nitrogen source, dilution effect and growth medium) using Saccharomyces cerevisiae. Methodology and results: A total of six parameters were tested for optimising bioethanol production i.e. pH, temperature, inoculum size, nitrogen source, dilution effect and types of medium. Results showed that the optimum conditions for OPT sap in bioethanol production were at pH 4.0, temperature of 30 °C, inoculum size of 10 % (v/v), without requirement of nitrogen supplementation and substrate dilution. A fermentation period of 24 h was best for bioethanol production and resulted in bioethanol production, formation rate and yield of 47.5 g/L, 1.98 g/h and 0.50 g/g, respectively. Conclusion, significance and impact study: The study has clearly demonstrated that high efficient bioethanol production from OPT sap is possible but it is susceptible to various fermentation influencing parameters. This study could establish an effective and sustainable utilisation of waste OPT especially its sap as a lignocellulosic biomass supplement from the oil palm industry for second generation biofuel production.
Saccharomyces cerevisiae ; Fermentation

As a new beer fermentation technology, high temperature and high gravity fermentation has brought many benefits to brewery industry, but there are also a series of problems such as the decrease of yeast flocculation ability at the end of fermentation and the high concentration of higher alcohols. To increase yeast flocculation ability and reduce the production of higher alcohols in high temperature and high gravity fermentation of beer, BAT2 was replaced by the FLO5 expression cassette to obtain the mutant strain S6-BF2. Real-time quantitative PCR showed that the relative transcriptional level of FLO5 in S6-BF2 improved 17.8 times compared with that in S6. The flocculation ability of mutant S6-BF2 heightened by 63% compared to that of the original strain S6, and the concentration of higher alcohols decreased from 175.58 mg/L to 159.58 mg/L in high temperature and high gravity fermentation of beer. Moreover, the activity of mitochondrial branched-chain amino acid transferase was repressed, resulting in the production of higher alcohols of 142.13 mg/L, reduced by 18.4% compared to that of the original strain S6, meanwhile, the flocculation ability of mutant S6-BF2B1 kept unchanged compared to the mutant S6-BF2. The determination result of flavor compounds showed that the higher alcohols/ester ratio in beer was reasonable. This research has suggested an effective strategy for enhancing yeast flocculation ability and decreasing production of higher alcohols in high-temperature and high-gravity brewing.
Beer ; Fermentation ; Hypergravity ; Saccharomyces cerevisiae ; Saccharomyces cerevisiae Proteins ; Temperature ; Transaminases

CRISPR/Cas9 has been widely used in engineering Saccharomyces cerevisiae for gene insertion, replacement and deletion due to its simplicity and high efficiency. The selectable markers of CRISPR/Cas9 systems are particularly useful for genome editing and Cas9-plasmids removing in yeast. In our previous research, GAL80 gene has been deleted by the plasmid pML104-mediated CRISPR/Cas9 system in an engineered yeast, in order to eliminate the requirement of galactose supplementation for induction. The maximum artemisinic acid production by engineered S. cerevisiae 1211-2 (740 mg/L) was comparable to that of the parental strain 1211 without galactose induction. Unfortunately, S. cerevisiae 1211-2 was inefficient in the utilization of the carbon source ethanol in the subsequent 50 L pilot fermentation experiment. The artemisinic acid yield in the engineered S. cerevisiae 1211-2 was only 20%-25% compared with that of S. cerevisiae 1211. The mutation of the selection marker URA3 was supposed to affect the growth and artemisinic acid production. A ura3 mutant was successfully restored by a recombinant plasmid pML104-KanMx4-u along with a 90 bp donor DNA, resulting in S. cerevisiae 1211-3. This mutant could grow normally in a fed-batch fermentor with mixed glucose and ethanol feeding, and the final artemisinic acid yield (> 20 g/L) was comparable to that of the parental strain S. cerevisiae 1211. In this study, an engineered yeast strain producing artemisinic acid without galactose induction was obtained. More importantly, it was the first report showing that the auxotrophic marker URA3 significantly affected artemisinic acid production in a pilot-scale fermentation with ethanol feeding, which provides a reference for the production of other natural products in yeast chassis.
Artemisinins ; Fermentation ; Saccharomyces cerevisiae/metabolism* ; Saccharomyces cerevisiae Proteins/metabolism*

Yeast cell wall plays an important role in the establishment and maintenance of cell morphology upon the cell wall stress. The cell wall of yeast consists of β-glucans, mannoproteins and chitin. The composition and structure remodel due to cell wall stress. Brewer's yeast cell wall exhibits stress response during long-term acclimation in order to adapt to environmental changes. This paper reviews the composition and structure of yeast cell wall and the molecular mechanisms of cell wall remodeling and signal pathway regulation.
Cell Wall ; Chitin ; Saccharomyces cerevisiae

Sterols, a class of cyclopentane poly-hydrophenanthrene derivatives, are the predominant membrane constituent of eukaryotes. These substances have a variety of biological activities and have been widely used in food and pharmaceutical industries. The presence of endogenous ergosterol biosynthetic pathway in Saccharomyces cerevisiae cells make it an ideal chassis for the de novo synthesis of sterol and its derivatives. Most recently, the rational modification of organelles provides a novel strategy for the directed transportation and storage of target products and the ultimate enhanced product synthesis. This review summarizes the phenotypic responses of S. cerevisiae cells upon different physiological stimulations and the underlying molecular mechanisms. Reinforcement of sterol production through directed storage, transportation, and excretion of sterols offers a novel strategy for breaking the limitation of de novo biosynthesis of sterols in yeast.
Ergosterol ; Phytosterols ; Saccharomyces cerevisiae ; Sterols

Saccharomyces cerevisiae/genetics* ; Ergosterol ; Fermentation

Lager yeast is the most popular yeast strain used for beer production in China. The flocculation of yeast plays an important role in cell separation at the end of fermentation. Therefore, appropriately enhancing the flocculation capability of the lager yeast without affecting its fermentation performance would be desirable for beer industry. Our previous study showed that the defect of gene RIM21 might contribute to the enhanced flocculation capability of a lager yeast G03. To further investigate the role of the RIM21 gene in flocculation of strain G03, this study constructed a RIM21-deleted mutant strain G03-RIM21Δ through homologous recombination. Deletion of RIM21 improved the flocculation capability of strain G03 during wort fermentation at 11 °C without changing its fermentation performance significantly. The expression of FLO5, Lg-FLO1 and some other genes involved in cell wall integrity pathway were up-regulated in strain G03-RIM21Δ. In addition, the disruption of RIM21 enhanced resistance of yeast cells to cell wall inhibitors. These results provide a basis for elucidating the flocculation mechanism of lager yeast under low-temperature fermentation conditions.
Beer ; Fermentation ; Flocculation ; Receptors, Cell Surface ; Saccharomyces/metabolism* ; Saccharomyces cerevisiae/metabolism* ; Saccharomyces cerevisiae Proteins/metabolism*

The target of rapamycin (TOR) signaling pathway is a conserved pathway that regulates eukaryotic cell growth in response to environmental cues. Chemical genomic approaches that profile rapamycin sensitivity of yeast deletion strains have given insights into the function of TOR signaling pathway. In the present study, we analyzed the rapamycin sensitivity of yeast deletion library strains on synthetic medium. As a result, we identified 130 strains that are hypersensitive or resistant to rapamycin compared with wild-type cells. Among them, 36 genes are newly identified to be related to rapamycin sensitivity. Moreover, we found 16 strains that show alteration in rapamycin sensitivity between complex and synthetic media. We suggest that these genes may be involved in part of TOR signaling activities that is differentially regulated by media composition.
Cues ; Eukaryotic Cells ; Saccharomyces ; Saccharomyces cerevisiae ; Sirolimus ; Yeasts

OBJECTIVETo construct strains containing green fluorescent protein (GFP) to study gene regulation in Saccharomyces albicans cells during the infection process.

METHODSpACT1-GFP was constructed, and Saccharomyces albicans CAI4 was transformed. The expression of GFP in yeast and hyphal compartments was observed with microscopy.

RESULTS99% of Saccharomyces albicans cells containing pACT1-GFP fusion displayed significant fluorescence levels both in the yeast and hyphal compartments. The fluorescence intensity in two compartments had no obvious difference.

CONCLUSIONpACT1-GFP can be expressed stably in the yeast cells.

Vitis hybrid (Sheridan)-Robus coreanus red wine was vinified by fermentation of a mixture of Vitis hybrid and Robus coreanus must at 25degrees C for 10 days. The Vitis hybrid-Robus coreanus red wine had ethanol contents of 10.9%. It had high antihypertensive angiotensin I-converting enzyme (ACE) inhibitory activity of 57.8% and antioxidant activity of 64.8%. Changes in the physicochemical properties and functionality of the Vitis hybrid-Robus coreanus red wine was investigated during a post-fermentation period of three months. The ACE inhibitory activity of the red wine increased as the post-fermentation period prolonged, and showed the highest ACE inhibitory activity of 70.4% 60 days post-fermentation. However, the antioxidant activity declined significantly to 47.2% during the post-fermentation period of 60 days. In terms of sensory evaluation, the Vitis hybrid-Robus coreanus red wine had the best acceptability 60 days post-fermentation.
Chimera ; Ethanol ; Fermentation ; Peptidyl-Dipeptidase A ; Saccharomyces ; Saccharomyces cerevisiae ; Vitis ; Wine