Bacteria are always single-celled, and quite frankly, I don't know why the ones in question are such a big deal, there are plenty of prokaryotes that thrive under anaerobic conditions.
Having seen enough exceptions in biology, I wouldn’t be surprised if someone found a multicellular bacterial species that violates everything we know about bacteria. Biology is completely wild, and it’s really hard to come up with a rule or a category that always works and nobody has any problems with it.
Nice article, but that headline is so misleading, I'm not inclined to upvote it.
tl;dr: Microorganisms used to live without oxygen. Some organisms started sprewing oxygen. Oxygen killed off most of these oxygen-free microorganisms. Life evolved and adapted. There's this lake in which the bottom layer is oxygen-less and oxygen-free microorganisms exist there. Scientists are doing a bunch of studies of this ecosystem.
I wouldn't call those organisms "alien." They were first in this planet!
