Is true bacteria multicellular or unicellular?

Answer 1

Many bacteria are free-living unicellular (single celled) organisms, but many also form colonies of genetically identical individuals, and a few are multicellular. It is a common misconception that all bacteria are unicellular.

Multicellular bacterial organisms have specialized cells, and the whole organism can't survive without those cells. For example, Nostoc, a species of cyanobacteria, forms multicellular strands. Some cells in the strand fix nitrogen, providing an important resource to the other cells in the strand, which carry out photosynthesis. Without the nitrogen provided by the nitrogen-fixing cell, the others couldn't survive, and without the sugars produced by the photosynthetic cells, the nitrogen-fixing ones would die. Because the individual cells would not survive if they were separated, Nostoc is considered to be multicellular.