Life-form of the Month: Yeast
opinionator.blogs.nytimes.com
opinionator.blogs.nytimes.com
But the title of life form of all millennia has to go to the mitochondria.
After all there wouldn't be any multicelled animals if it wasn't for it.
For what it's worth Yoghurt is produced by bacterial fermentation usually with Lactobacillus bulgaricus and Streptococcus thermophilus, not by a Saccharomyces ferment.