The prokaryote colony is a large mass of pathogens that are neutral. They only appear underwater, making them hard to find. They will attack when they are disturbed at all, even if tey are just touched. The prokaryote colony attacks you by poisoning you. then raming you into blocks, or other mobs.
The prokaryote colony appears in
Atlantis dimension : levels 8 - 40 (underwater)
Overworld : levels 4 - 20 (underwater)