Bacteria are among the smallest living things. A single bacterium consists of just one cell. Not all bacteria are harmful. There are different unicellular organisms and types of bacteria.

Bacteria are among the smallest living things. A single bacterium consists of just one cell. Not all bacteria are harmful. There are different unicellular organisms and types of bacteria.

"The fact that terrestrial microbes are the Earth's best colonizers means we can never completely discount terrestrial ...