Stress tolerance and growth physiology of yeast strains from the Brazilian fuel ethanol industry
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ORIGINAL PAPER
Stress tolerance and growth physiology of yeast strains from the Brazilian fuel ethanol industry B. E. Della-Bianca • A. K. Gombert
Received: 21 June 2013 / Accepted: 5 September 2013 / Published online: 24 September 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract Improved biofuels production requires a better understanding of industrial microorganisms. Some wild Saccharomyces cerevisiae strains, isolated from the fuel ethanol industry in Brazil, present exceptional fermentation performance, persistence and prevalence in the harsh industrial environment. Nevertheless, their physiology has not yet been systematically investigated. Here we present a first systematic evaluation of the widely used industrial strains PE-2, CAT-1, BG-1 and JP1, in terms of their tolerance towards process-related stressors. We also analyzed their growth physiology under heat stress. These strains were evaluated in parallel to laboratory and baker’s strains. Whereas the industrial strains performed in general better than the laboratory strains under ethanol or acetic acid stresses and on industrial media, high sugar stress was tolerated equally by all strains. Heat and low pH stresses clearly distinguished fuel ethanol strains from the others, indicating that these conditions might be the ones that mostly exert selective pressure on cells in the industrial
B. E. Della-Bianca A. K. Gombert (&) Department of Chemical Engineering, University of Sa˜o Paulo, PO Box 61548, Sa˜o Paulo, SP 05424-970, Brazil e-mail: [email protected] Present Address: A. K. Gombert Faculty of Food Engineering and Bioenergy Laboratory, University of Campinas (UNICAMP), Rua Monteiro Lobato, 80, Campinas, SP 13083-862, Brazil
environment. During shake-flask cultivations using a synthetic medium at 37 °C, industrial strains presented higher ethanol yields on glucose than the laboratory strains, indicating that they could have been selected for this trait—a response to energy-demanding fermentation conditions. These results might be useful to guide future improvements of large-scale fuel ethanol production via engineering of stress tolerance traits in other strains, and eventually also for promoting the use of these fuel ethanol strains in different industrial bioprocesses. Keywords Saccharomyces cerevisiae Fuel ethanol production Stress tolerance Growth physiology Industrial fermentation
Introduction As one of the largest ethanol producers in the world, Brazil has played a key role in the bioenergy scenario during recent years. The Brazilian 1st generation (1G) ethanol, recently classified as an advanced biofuel (US Environmental Protection Agency 2010) and the most ecoefficient 1G ethanol (Macedo 2007), is produced primarily by fed-batch fermentation of sugarcane juice and/or molasses. Cell recycling is used to achieve high cell concentrations in the fermentors, which decreases fermentation times and increases ethanol yields (Basso et al. 2011; Della-Bianca et al. 2013).
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Baker’s strains of the yeast Saccharo
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