Adaptive evolution in enhancing wine yeast.
Colin McBryde (1), Miguel de Barros Lopes (2), Vladimir Jiranek (1)
(1) School of Agriculture and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia; (2) School of Pharmacy and Medical Sciences, Division of Health Sciences, University of South Australia, GPO Box 2471, Adelaide, SA, 5001, Australia
Adaptive evolution defines a set of mutations that occur in response to a specific challenge and are advantageous to the cell. During serial or continuous cultivation in the presence of an environmental stress, an increase in fitter variants occurs due to natural selection. We used this technique to isolate adaptively evolved mutants of the commercial Saccharomyces cerevisiae strain L-2056 (Lallemand, Australia) and strain C9 ( hoD MAT a), a haploid derivative thereof. The selective condition chosen was extended anaerobic fermentation using a sequential batch system. Parental cultures were inoculated at low cell densities into chemostats containing a chemically defined grape juice media and upon completion each batch acted as the inoculum for a subsequent fermentation. Isolates collected every 50 generations were screened in small-scale fermentations under near-anaerobic conditions. Isolate FM5, taken after around 250 generations from the C9 culture and isolate FM16, taken from the L-2056 culture after some 350 generations, performed better under the imposed conditions. Both catabolised the supplied sugar within a shorter period. Also, glycerol yields by these mutants were higher than the respective parental strain. Changes in transcriptional regulation in the mutants were analysed by microarray technology. We propose that adaptive evolution is effective for isolation of strains that are highly tailored to the stressful conditions of a typical wine fermentation.