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Open Access Original article

Isolation and characterization of a resident tolerant Saccharomyces cerevisiae strain from a spent sulfite liquor fermentation plant

Violeta Sànchez i Nogué1, Maurizio Bettiga12 and Marie F Gorwa-Grauslund1*

Author Affiliations

1 Division of Applied Microbiology, Lund University, P.O. Box 124, SE-221 00, Lund, Sweden

2 Current address: Industrial Biotechnology, Department of Chemical and Biological Engineering, Chalmers University of Technology, Göteborg, Sweden

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AMB Express 2012, 2:68  doi:10.1186/2191-0855-2-68

Published: 13 December 2012

Abstract

Spent Sulfite Liquor (SSL) from wood pulping facilities is a sugar rich effluent that can be used as feedstock for ethanol production. However, depending on the pulping process conditions, the release of monosaccharides also generates a range of compounds that negatively affect microbial fermentation. In the present study, we investigated whether endogenous yeasts in SSL-based ethanol plant could represent a source of Saccharomyces cerevisiae strains with a naturally acquired tolerance towards this inhibitory environment. Two isolation processes were performed, before and after the re-inoculation of the plant with a commercial baker’s yeast strain. The isolates were clustered by DNA fingerprinting and a recurrent Saccharomyces cerevisiae strain, different from the inoculated commercial baker’s yeast strain, was isolated. The strain, named TMB3720, flocculated heavily and presented high furaldehyde reductase activity. During fermentation of undiluted SSL, TMB3720 displayed a 4-fold higher ethanol production rate and 1.8-fold higher ethanol yield as compared to the commercial baker’s yeast. Another non-Saccharomyces cerevisiae species, identified as the pentose utilizing Pichia galeiformis, was also recovered in the last tanks of the process where the hexose to pentose sugar ratio and the inhibitory pressure are expected to be the lowest.

Keywords:
Saccharomyces cerevisiae; Spent sulfite liquor fermentation; PCR-fingerprinting; Stress tolerance; Resident yeast