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Baker's yeast, or Saccharomyces cerevisiae, has been used in cooking and brewing for centuries, and more recently has also proved a valuable asset in molecular- and cell-biology research. However, the genomes of this species' many strains had never been compared on a large scale. Leonid Kruglyak, a geneticist at Princeton University in New Jersey, and his colleagues set out to do this, both to provide information on genetic variation in this microorganism and to learn about the evolutionary relationships among different strains. Using DNA microarrays, the team uncovered almost 1.9 million single-letter variations — known as single nucleotide polymorphisms — in the DNA code among the genomes of 63 strains. On page 342, their study of yeasts from around the globe reveals that S. cerevisiae is a diverse, highly adaptable species. Kruglyak tells Nature more.

How did you gather the different strains?

We requested samples from researchers and repositories around the world and received more than 100 strains. For the strains to be useful, they had to be able to produce spores that could mate with other strains. Some strains couldn't make spores, so we ended up with 63 that were usable.

Did you find genetic similarities between strains from different geographical areas?

Yes. Vineyard strains from many parts of Europe, as well as North America and Africa, are very similar, which is no accident — clearly these strains have been transferred across continents by people. One strain we studied is classified as coming from a vineyard in Russia, but doesn't look like any other wine strain we looked at. So either they're making wine from a strain unrelated to that being used by everyone else, or it was simply misclassified.

How adaptable is S. cerevisiae?

Very. We found that strains isolated from human patients are diverse. Several looked like vineyard strains, three bore some similarity to those used in making beer and bread, and some didn't resemble any other strains. We interpret this to mean that there isn't a particular subgroup that has specialized to colonize human tissues. Instead, whatever strain happens to be in the environment can probably make the transition.

Does this finding have implications for human health?

There have been reports of patients being infected with strains that are sold as probiotic nutritional supplements. This suggests that taking yeast as a supplement may not be a good idea for people with compromised immune systems.