Bacillus subtilis, sometimes known as B. subtilis, is a Gram-positive bacterium that belongs to the prokaryotic microorganism domain.
Prokaryotic cells are single-celled microorganisms that comprise archaea and bacteria and are thought to be the world's oldest.
These cells often exist on their own or in the guts of other species. The cells are made up of cytoplasm and have a single membrane. Certain prokaryotic cells use cyanobacteria within them to perform photosynthesis.