Saccharomyces uvarum (cryotolerant aka cold fermenting) is found in the wild in both Europe and the Americas, and at least according to the Libkind and Hittinger paper is “associated with beer as [a] contaminant” and “with cider or wine fermented at low temperatures”. This is species B strain in the paper.

Saccharomyces eubayanus (cryotolerant aka cold fermenting) is the new species proposed in the paper that was discovered in the Patagonia region of South America. Apparently Patagonian natives used to make a fermented beverage from the beech tree galls where the yeast was collected. The galls are created by Cyttaria, a parasitic fungus living on the beech trees that produces fruiting bodies rich in fermentable sugars, so this form of indigenous “beer”  was actually a double fungus drink, with one fungus (yeast) fermenting another fungus (Cyttaria), which is kind of cool. This is species A strain in the paper.

Saccharomyces bayanus (cryotolerant aka cold fermenting) is, like S. pastorianus, a hybrid, but does S. pastorianus one better by being a triple hybrid of primarily S. uvarum and S. eubayanus (seems to vary between roughly 1/3 to 2/3 S. uvarum, with S. eubayanus making up the other 1/3 to 2/3, depending on the strain), with a dash of S. cerevisiae thrown in for good measure.  S. bayanus is “associated with beer as [a] contaminant” according to the Libkind and Hittinger paper.

An interesting corollary to all this is that modern lager yeast is actually quite a bit younger than one might expect.  The conventional wisdom, at least as I used to understand it, was that Germans started lagering (storing) beer in caves about 600 years ago, and that the cooler conditions selected for more crytotolerant yeast strains over time.  While that may well be true as far as it goes, it appears that S. eubayanus must have traveled to the new world on some human related vector, such as timber, insects, clothing, barrels, or some such.  This is because S. eubayanus does not appear to exist in the wild anywhere in the world except for Patagonia, and it needed to be present in Europe sometime before Hansen first isolated lager yeast in the late 19th century.  Thus, the window for a hybridization event between Saccharomyces cerevisiae and Saccharomyces eubayanus is roughly bookended by the start of new world exploration by the Europeans around 1500 and the isolation of lager yeast a bit before 1900.  Libkind’s best guess is that the event occurred sometime between 1600 and 1800, and I like to imagine a fairly tame domesticated S. cerevisiae strain getting cozy in a barrel of lager in a Bavarian cave somewhere when a wild eyed S. eubayanus strain bursts in and has it’s way with the unsuspecting old world yeast cell, creating a whole greater at making tasty, cold-fermented beer than the sum of its parts.

Hopefully that sheds a bit of light on lager yeast and the scientific nomenclature surrounding it.  Here are some additional interesting tidbits on where the various scientific words come from:

The roots of the word Saccharomyces basically mean “sugar fungus”. (Greek sakkharon, sugar) and [Greek mukēs, mukēt–, fungus or mushroom.] – http://www.affixes.org/m/-myces.html

Similarly, Brettanomyces is “British Fungus”.

Despite the Greek ending, genus names ending in -myces sometimes refer to bacteria, because they were originally thought to be fungi. Examples are Saccharomyces (Greek sakkharon, sugar), the genus of fungi that includes baker’s and brewer’s yeasts, and Streptomyces (Greek streptos, twisted), a genus of bacteria, several of which are important sources of antibiotics. – http://www.affixes.org/m/-myces.html

Cerevisiae is based on Ceres, the Roman god goddess of grain – Cerevisiae apparently literally means beer in Latin.