Natural populations of Saccharomyces kudriavzevii in Portugal are associated with oak bark and are sympatric with S. cerevisiae and S. paradoxus

Abstract

Here we report the isolation of four Saccharomyces species (former Saccharomyces sensu stricto group) from tree bark. The employment of two temperatures (10 degrees C in addition to the more commonly used 30 degrees C) resulted in the isolation of S. kudriavzevii and S. uvarum, two species that grow at low temperatures, in addition to S. cerevisiae and S. paradoxus. A clear bias was found toward the bark of certain trees, particularly certain oak species. Very often, more than one Saccharomyces species was found in one locality and occasionally even in the same bark sample. Our evidence strongly suggests that (markedly) different growth temperature preferences play a fundamental role in the sympatric associations of Saccharomyces species uncovered in this survey. S. kudriavzevii was isolated at most of the sites sampled in Portugal, indicating that the geographic distribution of this species is wider than the distribution assumed thus far. However, the Portuguese S. kudriavzevii population exhibited important genetic differences compared to the type strain of the species that represents a Japanese population. In this study, S. kudriavzevii stands out as the species that copes better with low temperatures.

FIG. 1.

Maximum-parsimony phylogenetic trees of Saccharomyces spp. obtained with sequences of D1/D2 domains of the 26S rDNA (a), complete ITS region (ITS1, 5.8S, and ITS2) (b), partial nuclear MET6 gene (c), and partial GAL1 gene (d). The organisms chosen to root the trees were Kazachstania servazzii (a), S. cerevisiae (b), S. cerevisiae and S. paradoxus (c), and Naumovia castellii (d). The D1/D2, ITS, and GAL1 trees are the single most parsimonious trees, and the MET6 tree is a consensus tree of the 15 most parsimonious trees. Numbers at the nodes are bootstrap values (1,000 replicates; values below 50% are not shown). GenBank accession numbers of the sequences are indicated after strain designations. The sequences without GenBank accession numbers were retrieved from the fungal sequence alignment section of the SGD (http://www.yeastgenome.org/). Sequences determined in this study are shown in boldface type. Type strains are indicated with a superscript T.

FIG. 2.

Specific growth rates of S. kudriavzevii ZP 591 and S. cerevisiae ZP 567 measured at 6, 10, 25, and 30°C in media with glucose (GLU), fructose (FRU), and raffinose (RAF) as the sole carbon sources. Standard deviations (error bars) are shown.

FIG. 3.

Maximum growth temperatures of a set of 35 strains of S. cerevisiae (12 strains) S. kudriavzevii (11 strains), S. paradoxus (8 strains), and S. uvarum (4 strains). All strains were isolated during the present work.