Winogradsky column

In a Winogradsky column the conditions change from oxygen-rich (aerobic) at the top of the column to oxygen-deficient (anaerobic) at the bottom. Different microorganisms develop in the various environmental niches throughout the column. The products of one microbe's metabolic activities support the growth of another microbe. The result is that the column becomes a self-supporting ecosystem, which is driven only by the energy received from the incoming sunlight. Winogradsky columns are easily constructed, and are often used in classroom experiments and demonstrations.

The Winogradsky column is named after Sergius Winogradsky, a Russian microbiologist who was one of the pioneers of the study of the diversity of the metabolic activities of microorganisms.

To set up a Winogradsky column, a glass or clear plastic tube is filled one-third full with a mixture of mud obtained from a river bottom, cellulose, sodium sulphate, and calcium carbonate. The remaining two-thirds of the tube is filled with lake or river water. The capped tube is placed near a sunlit window.

Over a period of two to three months, the length of the tube becomes occupied by a series of microbial communities. Initially, the cellulose provides nutrition for a rapid increase in bacterial numbers. The growth uses up the available oxygen in the sealed tube. Only the top water layer continues to contain oxygen. The sediment at the bottom of the tube, which has become completely oxygen-free, supports the growth only of those bacteria that can grow in the absence of oxygen. Desulfovibrio and Clostridium will predominate in the sediment.

Diffusion of hydrogen sulfide produced by the anaerobic bacteria, from the sediment into the water column above supports the growth of anaerobic photosynthetic bacteria such as green sulfur bacteria and purple sulfur bacteria. These bacteria are able to utilize sunlight to generate energy and can use carbon dioxide in a oxygen-free reaction to produce compounds needed for growth.

The diminished hydrogen sulfide conditions a bit further up the tube then support the development of purple sulfur bacteria such as Rhodopseudomonas, Rhodospirillum, and Rhodomicrobium.

Towards the top of the tube, oxygen is still present in the water. Photosynthetic cyanobacteria will grow in this region, with the surface of the water presenting an atmosphere conducive to the growth of sheathed bacteria .

The Winogradsky column has proved to be an excellent learning tool for generations of microbiology students, and a classic demonstration of how carbon and energy specifics result in various niches for different microbes, and of the recycling of sulfur, nitrogen, and carbon.

See also Chemoautotrophic and chemolithotrophic bacteria; Methane oxidizing and producing bacteria