The yeast apocalypse cometh

Partly human yeast show a common ancestor's lasting legacy -- ScienceDaily

I've been writing about yeast for a while now, and contemplating ideas of yeast apocalypse of varying degrees of seriousness:

a.  cosmic ray mutated yeast on board a spaceship or colony becomes particularly well adapted to the human gut, causing nearly all people therein to be continually drunk;

b.  genetically engineered yeast to make fake milk goes rampant in the environment and causes thousands of  brewers to get obnoxious, cloudy, cheesey beer;

c.  genetically engineered yeast to make opiates goes rampant in the environment and gives all home brewers a morphine addiction.

 Now, with the story above about how many genes humans and yeast share, I can perhaps go further, and get some sort of yeast/human genetic cross over resulting in the yeast-ification of the human species.  Not exactly as exciting as The Fly, I guess; rather more like the original The Thing from Another World.  (It was an evolved vegetable, after all.)