Population genetic structure of the ancestor of the Lager-brewing yeast in Patagonia (Saccharomyces eubayanus)

EIZAGUIRRE, J.; PERIS, D.; DE LOS RIOS, P.; LOPES, C.; RODRIGUEZ, M.E.; HITTINGER, C.; LIBKIND, D.

Bariloche

Congreso; 5th Argentinean Congress on Bioinformatics and Computational Biology; 2014

The discovery and description in Patagonia of a new species of yeast, Saccharomyces eubayanus, parental of the inter-specific hybrid S. pastorianus (used worldwide in the production of LAGER beer) opened a very fertile field for research, development and innovation. This work aims to contribute to the knowledge on the biogeography of S.eubayanus along the Andean Patagonia and the genetic structure of its populations. To do this more than 200 isolates of S. eubayanus were obtained from various substrates (soil, bark, leaves and Cyttaria spp.) associated with various tree species of the endemic genus Nothofagus in Argentina and Chile (between latitudes 37C to 54C). The isolates were identified by PCR-fingerprinting and then, along with LAGER-brewing strains, were characterized by sequencing and analysis of COX2 (mitochondrial, 530bp) and DCR1 (nuclear, 859bp). Both genes proved to be useful for detecting intra-specific variability in the studied species. A database of the isolate´s source coordinates, altitude, type of substrate, host tree and other ecological parameters such precipitation, radiation and mean temperaturas, was generated. Geographical distance of the isolates was calculated and a principal component analysis of ecological traits was performed. The results with DCR1 gene discriminated two main populations with a genetic divergence of  1%. 29% of the strains tested was part of the "A" population (21 haplotypes) located exclusively in northern Patagonia, and "B" population (47 haplotypes) consisted of remaining strains tested and these were distributed throughout Patagonia. This is consistent with results obtained using fewer strains employing SNPs markers  10KB at genomic level. With the COX2 gene, both populations were not evidenced but we found at least 55 haplotypes. Moreover, the COX2 gene showed that 7 strains appeared to be recombinants between S.eubayanus and a second species: Saccharomyces uvarum; which is sympatric and closely related to S.eubayanus. Phylogenetic networks analysis were performed which allowed a better understanding of the reticulated evolution of populations of S.eubayanus were generated. The results showed the existence of two populations of S.eubayanus markedly different in Patagonia and that at the same time exhibit high intra-population genetic heterogeneity. The population of greater abundance and distribution (B) was the closest (genetically) to LAGER strains although none of the isolates showed 100% similarity. In this paper, hypotheses about environmental and geological factors influencing the population structure of this species are addressed. This yeast species has biotechnological importance for the production of beers with Patagonian regional identity.