Winogradsky column
The Winogradsky column is used for the isolation of phototrophic green and purple bacteria and other anaerobes . It is named after the Russian microbiologist Sergei Nikolajewitsch Winogradski . They developed it in the 1880s to study soil organisms .
The column represents an anaerobic (without the presence of atmospheric oxygen) ecosystem in miniature format and can also be a source for many types of prokaryotes that are involved in the nutrient cycle over a longer period of time . The column was used in the enrichment of a wide variety of aerobic and anaerobic prokaryotes. The advantage of the column consists on the one hand in the easy availability of inocula (see inoculation ), but also in the fact that it can be selectively enriched with compounds whose decomposition processes are to be investigated. Microorganisms that are able to break down the examined substrate can thus be “picked”.
Another advantage of the column is that it resembles a natural habitat much more than a liquid culture medium which is inoculated with a sample. Thus, a variety of physiological types of microorganisms can be observed, whereas in an enrichment culture, faster growing species would quickly displace the slower growing ones.
Manufacturing
A Winogradsky column is made in a glass cylinder. This is filled to ≈1 / 3 with sludge, which is rich in organic substances and also contains sulphides . First, carbon substrates are added to the sludge. Various organic additives were used in the past. This includes hay, chopped up newspaper, sawdust, shredded leaves or root material, minced meat, hard-boiled eggs and sometimes dead animals. Furthermore, calcium carbonate (CaCO 3 ) and calcium sulfate (CaSO 4 ) are added, which serve as a buffer and a source of sulfate in the sludge. The sludge is pressed firmly into the cylinder, being careful not to trap any atmospheric oxygen. The mud is then covered with water (from a pond, lake or ditch) and sealed with aluminum foil or, as shown in the picture, with parafilm . The cylinder is placed in the light to ensure a sufficient supply of sunlight. However, care must be taken that it is not exposed to excessive radiation.
Typically, a mixture that contains many different types of microorganisms develops in the Winogradsky column. In the upper area, cyanobacteria and algae quickly form. As these produce oxygen (O 2 ), this zone quickly becomes oxic. Fermentative decomposition processes that take place in the sludge lead to the production of organic acids , hydrogen (H 2 ) and alcohols . These are suitable substrates for sulfate-reducing bacteria . As a result of sulphide production, green and purple spots appear on the side facing the light. The green spots consist of green sulfur bacteria, the development of which often takes place in the lower layers of the column near the sulphide source. The purple spots, which consist of sulfur purple bacteria, are increasingly formed in the upper layers. This finding can be explained by a different sulfide tolerance of green and purple bacteria.
At the interface between water and sludge, there is (usually) a clear cloudiness and coloration of the water due to the growth of the purple sulfur bacteria and some other bacteria. Samples of phototrophic bacteria can be taken with the help of a pipette. This is done from little colored water or mud. Enrichment media ( culture media ) can be inoculated with these samples .
Anaerobic phototrophic bacteria
As a rule, four different families of anaerobic phototrophic bacteria can be found in the Winogradsky column. On the one hand, the order of the Chlorobiales (green bacteria). The family of the Chlorobiaceae (green sulfur bacteria) with the species Chlorobium limicola and the family of Chloroflexaceae (Chloroflexus group) with the species Chloroflexus aurantiacus should be mentioned here. On the other hand, the order of the Rhodospirillales (purple bacteria) with the families of the Chromatiaceae (sulfur purple bacteria) and the family of the Rhodospirillaceae (sulfur-free purple bacteria). These include the species Chromatium vinosum and Rhodospirillum rubrum .
literature
- Thomas D. Brock: Microbiology . 2nd corrected edition. Spectrum Akademischer Verlag, Heidelberg et al. 2003, ISBN 3-8274-0566-1 , ( spectrum textbook ).