The sulfur cycle

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 when decaying animals and plant debris. When decomposing proteins containing amino acids, including sulfur (cysteine, cystine, methionine), and decomposition of plant essential oils, hydrogen sulphide and mercaptan are formed. Hydrogen sulfide is released during the reduction of salts of sulfurous, sulfuric and sulfuric acids with the participation of sulfate-reducing bacteria and is also involved in the sulfur cycle.

In fact, hydrogen sulphide is not assimilated by plants, and accordingly, animals. Hydrogen sulphide oxidizes special sulfur bacteria, resulting in the formation of sulphate salts, which are very easily absorbed by plants. The sulfur-containing compounds synthesized by plants are also included in the sulfur cycle in nature. Ammonifying and sulfate-reducing bacteria release hydrogen sulphide from them. The sulfur cycle occurs, on the other hand, due to sulfur bacteria, oxidizing hydrogen sulphide.

Groups of sulfur bacteria

Serobacteria are divided into two groups: colorless and purple colored.

Colorless forms represent:

1) all kinds of Beggiatoa are long free-floating threads. Among them, the largest of all bacteria are observed;

2) some Thiothrix species are long immovable threads that attach to underwater objects;

3) several species of unicellular bacteria - Thiophysa.

All bacteria are autotrophs. The circulation of sulfur contributes to its accumulation inside the cell. In natural conditions, sulfur bacteria are found only in those places where hydrogen sulphide is formed constantly and where there is a free supply of oxygen. The movement of bacteria occurs in the bacterial plate. The sulfur cycle in the biosphere pushes the bacteria up behind the oxygen and down behind the hydrogen sulphide. The layer of bacteria in the Black Sea is located at a depth of about 200 m.

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 spare energy material.

If there is not enough hydrogen sulphide in the medium, the stored sulfur gradually oxidizes to sulfuric acid. It is neutralized by cellular bicarbonates and is released to the outside in the form of sulfuric acid salt.

The sulfur cycle can not do without the participation of purple sulfur bacteria, enriched with pigment bacteriopurpurin, giving them different shades of red, and photosynthetic pigment bacteriochlorophyll.

Serobacteria in nature are widespread. They live in sulfur springs, stagnant waters, mud, soil. Serobacteria are autotrophs, assimilate carbon dioxide, using the energy that is formed during the oxidation of the reduced sulfur compounds.

To 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 found in saline and fresh water bodies, in the soil.

The sulfur cycle is accompanied by regenerative processes caused by sulfur bacteria, which sometimes in nature reach huge sizes. In the Black Sea at a depth of more than 200 m contains so much hydrogen sulphide that life there completely ceases. With the accumulation of hydrogen sulphide in the soil, flooded with water, the life of plants and animals can stop on it.

Sulfate-reducing microbes form the healing sulfur mud of many lakes around Pyatigorsk, estuaries near Odessa and Evpatoria. These bacteria, when hydrogen sulphide is released, turn into a black mass of colloidal sulfur dioxide hydrate, which impregnates the silt of the reservoir. Corrosion of iron also occurs through their fault, which causes damage to the sewage and irrigation pipes.

Serobacteria are involved in biological wastewater treatment and are indicators of the strong soil and water contamination in human settlements.