any of a group of prokaryotic unicellular round spiral or rod-shaped single-celled micro-organisms that are often aggregated into colonies or motile by means of flagella, that live in soil, water organic matter or the bodies of plants and animals, and that are autotrophic saprophytic or parasitic in nutrition and important because of their biochemical effects and pathogenicity; a bacterium.

study of the molecules of the substances involved in the process of life; molecular biology.