Soil bacteria. Decomposition and putrefaction bacteria
Bacteria are the most important link in the general circulation of substances in nature.
1 cm³ of the surface layer of forest soil contains hundreds of millions of saprotrophic soil bacteria of several species.
Plants create complex organic substances from carbon dioxide, water and mineral salts of the soil. Many bacteria living in the soil, in the process of their vital activity, turn dead plant parts and dead organisms into humus.
They decompose complex substances into simple ones, which are used by plants again.
These are saprotrophic soil bacteria of putrefaction.
By converting organic residues into humus, they play a sanitary and soil-forming role in nature.
Another group of soil bacteria decomposes humus.
These are saprotrophic bacteria of fermentation.
In the process of their vital activity, humus turns into mineral salts necessary for plant life.
The economic value of bacteria of decay and fermentation
Many rotting bacteria cause food spoilage. Therefore, perishable foods are stored in refrigerators (at low temperatures, the vital activity of bacteria decreases). Since bacteria cannot live without water and die in salt and sugar solutions, food is dried, salted, pickled, candied, canned, and smoked. When canning, tightly closed jars are heated. In this case, not only bacteria die, but also their spores. Therefore, canned food is stored for a long time. Bacteria will spoil hay in haystacks if it is not dry enough. There are bacteria that spoil fishing nets, the rarest manuscripts and books in book depositories. To protect books from damage, they are fumigated with sulfur dioxide.
The souring of milk, fruit and berry juices is associated with the activity of fermentation bacteria. In this case, milk turns into sour milk, and juices – into a liquid with a high content of vinegar.
Milk is boiled for preservation, sterilized (destroy bacteria), stored in the refrigerator, and juices for long-term storage, as a rule, are canned in hermetically sealed jars or special packages.
During fermentation, lactic acid bacteria convert sugar into lactic acid, which inhibits the vital activity of putrefactive bacteria. A person uses this property of fermentation bacteria when pickling cabbage, pickling cucumbers, obtaining various lactic acid products from milk (sour cream, cottage cheese, cheese, etc.); the formation of silage from corn and other succulent plants. Some fermentation bacteria live in the intestines of humans and animals and aid in the digestion of food. These bacteria include, for example, E. coli.
Nitrogen-fixing nodule bacteria
Some soil bacteria are capable of absorbing nitrogen from the air, using it in life processes. These nitrogen-fixing bacteria live independently or live in the roots of legumes. Having penetrated the roots of legumes, these bacteria cause the growth of root cells and the formation of nodules on them. Such bacteria are called root nodules. These bacteria release nitrogen compounds that plants use. Bacteria receive carbohydrates and mineral salts from plants. Thus, there is a close relationship between the legume plant and the nodule bacteria, which is beneficial for both one and the other organism. This phenomenon is called symbiosis (from the Greek word symbiosis – “living together”).
Thanks to their symbiosis with nodule bacteria, legumes enrich the soil with nitrogen, thereby increasing the yield.