"Lactobacillus melindencis" (!).
Still working, with a bit of regular encouragement–Melinda's !
A useful explanatory sentence from one source:
"Microorganisms that release carbon dioxide as part of their life cycle can be used to leaven products."
The following is worth a look/read, even if you think you understand
leaven. What a mysterious thing it is--even to the chemists, I