Selection of High Ethanol-Producing Saccharomyces cerevisiae Strains, their Fermentation Properties, and Genetic Differentiation Based on rep-PCR


Irene G. Pajares1, Francisco B. Elegado*1,
Jose Paolo V. Magbanua1, and Asuncion K. Raymundo2

1National Institute of Molecular Biology and Biotechnology
2Institute of Biological Sciences, College of Arts and Sciences
University of the Philippines Los Baños, College Laguna

*Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.



Ten out of 37 Saccharomyces isolates statistically gave higher ethanol yields after 24 hours using 20% (total sugars) unsterile molasses medium. Saccharomyces cerevisiae 2025 and 2023 produced the highest ethanol concentrations of 8.7 % and 7.5% (v/v), respectively. In sterile molasses medium, ethanol production decreased with these two isolates, but increased with S. cerevisiae 2013, 2012, 2008, 2010 and 2014, with ethanol concentrations of 9.17, 8.88, 8.84, 8.44 and 8.31% (v/v), respectively. After 3 days incubation, all ten isolates survived at 40° C but only S. cerevisiae 2031 tolerated up to 15% (v/v) exogenous ethanol. S. cerevisiae 2010 and 2014 were resistant to the toxin produced by killer strain S. cerevisiae K1 (ATCC 60728). Combining the various test parameters, S. cerevisiae 2008, 2010 and 2014 would be ideal for industrial ethanol production and thus fingerprinted. Amplification of the mitochondrial small subunit ribosomal DNA (mtSSU rDNA) by polymerase chain reaction (PCR) detected polymorphisms among the S. cerevisiae strains. Cluster analysis using UPGMA-SAHN was able to group the high from the low ethanol producers but other properties such as ethanol and temperature tolerance were not distinctly separated. Repetitive sequence-based PCR analysis of the ten selected isolates using REP primers (rep-PCR) also clustered the three best S. cerevisiae isolates.



Rapid increase in the pump prices of fossil oil products like gasoline and the growing concerns on climate change, partly brought about by excessive carbon dioxide emission of motor vehicles fueled by fossil oils, have led to increased worldwide interests on the utilization of renewable fuels like ethanol. Fuel ethanol is used as additive to gasoline and as replacement for octane enhancers (such as benzene, butadiene and lead) that are known as noxious to the environment. Studies show that ethanol has a higher octane rating than gasoline and existing engines need not be modified at 10% ethanol blend. Research on ethanol fermentation, including the search for efficient Saccharomyces cerevisiae strains and other strains of closely related species, has been continuing for years in order to lower down the cost of production. Desired yeast strains have the special property of possessing particularly efficient aerobic and anaerobic metabolic capabilities, making them high ethanol producers. They could also possess other industrially-important properties such as ethanol tolerance, thermotolerance and resistance to killer yeasts...





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