Bioethanol strains of Saccharomyces cerevisiae characterised by microsatellite and stress resistance

Abstract

Strains of Saccharomyces cerevisiae may display characteristics that are typical of rough-type colonies, made up of cells clustered in pseudohyphal structures and comprised of daughter buds that do not separate from the mother cell post-mitosis. These strains are known to occur frequently in fermentation tanks with significant lower ethanol yield when compared to fermentations carried out by smooth strains of S. cerevisiae that are composed of dispersed cells. In an attempt to delineate genetic and phenotypic differences underlying the two phenotypes, this study analysed 10 microsatellite loci of 22 S. cerevisiae strains as well as stress resistance towards high concentrations of ethanol and glucose, low pH and cell sedimentation rates. The results obtained from the phenotypic tests by Principal-Component Analysis revealed that unlike the smooth colonies, the rough colonies of S. cerevisiae exhibit an enhanced resistance to stressful conditions resulting from the presence of excessive glucose and ethanol and high sedimentation rate. The microsatellite analysis was not successful to distinguish between the colony phenotypes as phenotypic assays. The relevant industrial strain PE-2 was observed in close genetic proximity to rough-colony although it does not display this colony morphology. A unique genetic pattern specific to a particular phenotype remains elusive.

Keywords: Contaminants; Fermentation; Microsatellite; Stresses; Yeasts.

Fig. 1

Colony (growing in YPD medium) and cells (magnification of 400× at optical microscopy) of a smooth colony (left) and a rough colony (right) of S. cerevisiae strains (Reprinted from Reis et al.⁴).

Fig. 2

Phenetic tree created with the microsatellite loci by using the Population 1.2.31 software and UPGMA clustering method. The legend inside the box is referent to the strain code (as in Table 1). Rough-colony strains are denoted in circles; smooth-colony strains in squares.

Fig. 3

Principal-Component Analysis (PC1 and PC2) of the yeast strains (rough-colony strains in circles; smooth-colony strains in squares) and the phenotypic characteristics. Numbers inside the circles and squares refer to the strain code as in Table 1. The legends in the vectors designate the phenotypic characteristics and the number in parentheses indicate the values (pH 1.25 and 1.5; E for ethanol, 13, 13.5, 14, 14.5%; G for glucose, 300, 400 and 500 g/L; S for sedimentation rate, above 10%) of the characteristic, as described in “Material and methods” section.