December 14, 2020 report
Researchers report evidence for two main domestication paths for bread yeast
A team of researchers affiliated with multiple institutions in France has found evidence for two main domestication paths for bread yeast. In their paper published in the journal Current Biology, the group studied the chromosomes of hundreds of commercial and sourdough yeast strains.
Humans have been using yeast to alter food and drinks for thousands of years. The most common uses have been making bread and beverages such as beer and wine. Over time, the process for making bread has been refined and has evolved into two main types: commercial and sourdough. In modern times, commercial bakers' yeast is used to make commercially sold bread. Sourdough bread is more complicated because it is made using sourdough starter—a mix of yeast, flour and other microbes, and even other yeasts, as a compound that is maintained over time, sometimes for generations. .
In this new effort, the researchers wondered if, over time, humans have domesticated the kinds of yeast that are used to make bread. To find out, they obtained samples of 31 strains of commercial yeast and 198 samples of sourdough strains from multiple sites across Europe. Each of the samples underwent chromosome analysis using flow cytometry to determine how related the strains were to one another. The researchers also studied data from other studies that sequenced the genomes of 17 strains of baker's yeast, along with 1,011 other yeast strains.
The researchers found that modern baker's yeasts are polyphyletic (meaning they came from more than a single common ancestor) and that most fit into one of two main clades. They also found that most modern strains are tetraploid—having four homologous sets of chromosomes, some of whose origins include yeasts used for making beer. The researchers also found that the sourdough strains typically had more copies of genes that encoded for proteins that carry and regulate isomaltase maltase and other enzymes than did baker's yeasts. They also found that baker's yeast appeared to have been selected for fast fermentation—most of them produced up to a gram of carbon dioxide in just 30 minutes.
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