Yeast hybridization: a solution for biodiversity conservation?

by Frederico Magalhães.

For thousands of years humans have been intuitively selecting plants or animals to crossbreed in order to improve the traits of the crops or livestock. A similar situation must have occurred with the yeast lineages associated with fermented beverages. Its close association with human activities has led to the so-called domestication of these species, resulting in industrial strains that perform remarkably well in each specific application, but whose performance may be severely reduced in a different environment (Steensels et al., 2014). The hybridization of yeast strains is one of the most important mechanisms leading to the generation of strains with improved properties and increasing the genetic diversity of yeasts. This can happen between different strains of the same species, different species of the same genus or even between strains of different genera. It is particularly relevant by the fact that the new species tend to display heterosis or hybrid vigour, that is, it has superior performance than both parental strains (Steensels et al., 2014). The most well-known yeast hybrid species is the one employed in the production of lager beer, S. pastorianus, an interspecific hybrid between S. cerevisiae and the cryotolerant S. eubayanus, which may have occurred as a contaminant in the brewing process, having selective advantage over the native S. cerevisiae yeast when fermentations were carried at low temperature (Gibson & Liti, 2015). The rapidly increasing knowledge in the yeast sexual life cycle as allowed the possibility to use targeted approaches for yeast breeding, which beyond the obvious advantages in terms of yeast performance and diversity are also considered GMO-free strategies, allowing its employment in food application as is the fermented beverages industry (Gibson & Liti, 2015).

Although the potentialities of industrial hybrid yeasts are fairly well documented, a recent work published in the Evolutionary Applications journal (Stelkens et al., 2014) propose that hybridization can also have an important impact in increasing evolutionary responsiveness and that taxa with the ability to exchange genes with distant relatives may have advantage in rapidly changing environments. This was shown by generating a set of F1 diploids obtained by crossing two haploids of the same species (S. paradoxus) and hybrids of S. paradoxus and S. cerevisiae and then inducing meiosis and haploid fusion to generate F2 populations. The obtained hybrids of F1 and F2 and parent populations were submitted to an environment with increasing salt concentration (from 0 to 160 g/L NaCl) to simulate a habitat that gradually deteriorates in quality. The results demonstrated that the F2 population persisted longer in deteriorating environments that the F1 population and these ones also had advantage in relation to the parental strains. Within the F2 population the interspecific hybrids (S. cerevisiae x S. paradoxus) showed higher resilience than the intraspecific ones (S. paradoxus x S. paradoxus). These results suggest that population facing environmental change may benefit from introgression and hybridization between distant species as the larger amounts of genetic variation seem to increase the likelihood of evolutionary rescue. Problems of genomic incompatibility and negative epistatic interactions must of course not be forgotten, particularly between more divergent populations, but these genetic approaches may have the potential to preserve the genetic variability of a species rather than distinct but frequently highly inbred local population.

References

Steensels et al., “Improving industrial yeast strains: exploiting natural and artificial diversity”, FEMS microbiology reviews, doi: 10.1111/1574-6976.12073, 2014.

Gibson & G. Liti, “Saccharomyces pastorianus: genomic insights inspiring innovation for industry”, Yeast, doi: 10.1002/yea.3033. 2015.

B. Stelkens et al., “Hybridization facilitates evolutionary rescue”, Evolutionary Applications, doi:10.1111/eva.12214, 2014.

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