A simple laboratory demonstration, the Winogradsky Columns, illustrates how different microorganisms perform their interdependent roles: the activities of one organism enable another to grow, and vice-versa. These columns are complete, self-contained recycling systems, driven only by energy from light.
Invented in the 1880s by Sergei Winogradsky, the device is a column of pond mud and water mixed with a carbon source such as newspaper (containing cellulose), blackened marshmallows or egg-shells (containing calcium carbonate), and a sulphur source such as gypsum (calcium sulphate) or egg yolk. Incubating the column in sunlight for months results in an aerobic/anaerobic gradient as well as a sulphide gradient. These two gradients promote the growth of different microorganisms such as Clostridium, Desulfovibrio, Chlorobium, Chromatium, Rhodomicrobium, and Beggiatoa, as well as many other species of bacteria, cyanobacteria, and algae.