Sulfur appears on the earth's surface as a result of volcanic activity in the form of compounds; in addition, water in some sources also contains hydrogen sulfide. The sulfur cycle is manifested by biological processes that are caused by microorganisms during rotting of animals and plant residues. Upon decomposition of proteins containing amino acids including sulfur (cysteine, cystine, methionine), and decomposition of plant essential oils, hydrogen sulfide and mercaptan are formed. Hydrogen sulfide is released during the recovery of salts of sulfurous, sulfuric and sulfurous acids with the participation of sulfate-reducing bacteria and is also involved in the sulfur cycle.
In fact, hydrogen sulfide is not absorbed by plants, and, accordingly, by animals. Hydrogen sulfide oxidizes special sulfur bacteria, resulting in the formation of sulfate salts, which are absorbed very well by plants. Sulfur-containing compounds synthesized by plants are also included in the sulfur cycle in nature. Ammonifying and sulfate-reducing bacteria release hydrogen sulfide from them. The sulfur cycle occurs, on the other hand, due to sulfur bacteria that oxidize hydrogen sulfide.
Groups of sulfur bacteria
Serobacteria are divided into two groups: colorless and purple stained.
Colorless forms represent:
1) all kinds of Beggiatoa - long free-floating threads. Among them, the largest of all bacteria are observed;
2) some types of Thiothrix are long fixed threads that attach to underwater objects;
3) several types of unicellular bacteria - Thiophysa.
All bacteria are autotrophs. The sulfur cycle contributes to its accumulation inside the cell. Under natural conditions, sulfur bacteria are found only in those places where hydrogen sulfide is constantly formed and where there is a free flow of oxygen. The movement of bacteria occurs in the bacterial plate. The sulfur cycle in the biosphere pushes bacteria upstream of oxygen and downstream of hydrogen sulfide. A layer of bacteria in the Black Sea is located at a depth of about 200 m.
The oxidation of sulfur bacteria with oxygen occurs in two stages. Initially, they are oxidized to sulfur, which is deposited in the protoplasm of cells and is used as a reserve energy material.
If there is not enough hydrogen sulfide in the medium, the stored sulfur is gradually oxidized to sulfuric acid. It is neutralized by cellular bicarbonates and is excreted in the form of sulfate salt.
The sulfur cycle is not complete without the participation of purple sulfur bacteria, enriched with the pigment bacteriopurpurine, which gives them different shades of red, and photosynthetic pigment bacteriochlorophyll.
Serobacteria in nature are widespread. They live in sulfur springs, stagnant waters, silts, soil. Serobacteria are autotrophs, assimilate carbon dioxide, using the energy that is generated during the oxidation of reduced sulfur compounds.
Colorless sulfur bacteria include thionic bacteria, such as Thiobacillus thioparus, Thiobacillus thiooxidans and others. In addition to hydrogen sulfide and sulfur, they also oxidize thio compounds, are autotrophs, are in salt and fresh water bodies, in the soil.
The sulfur cycle is accompanied by recovery processes caused by sulfur bacteria, which sometimes in nature reach enormous proportions. In the Black Sea, at a depth of more than 200 m, such a large amount of hydrogen sulfide is contained that life there completely ceases. With the accumulation of hydrogen sulfide in the soil flooded with water, the life of plants and animals can stop on it.
Sulfate-reducing microbes form the healing sulfuric mud of many lakes near Pyatigorsk, estuaries near Odessa and Yevpatoria. These bacteria, when hydrogen sulfide is released, turn into a black mass of colloidal sulfide iron hydrate, impregnating the sludge of a reservoir. Corrosion of iron also occurs through their fault, due to which sewer and irrigation pipes are damaged.
Serobacteria are involved in biological wastewater treatment and are indicators of severe soil and water pollution in settlements.