Different types of microorganisms develop not in isolation, but form complex communities – biocenoses, which are organized systems with various types of relationships between representatives of individual species (Symposium, 2005). Microorganisms interact in the environment foremost because these symbiotic relationships bring mutual benefit to microorganisms involved in this process. The joint growth of such organisms proceeds better, if compared to these organisms developing separately. An example of a symbiotic relationship is the symbiosis of green algae and infusoria. Algae, settling inside the body of the ciliates, uses the energy of light to convert CO2 into organic substances, thereby releasing oxygen (Symposium, 2005). The infusoria, in its turn, consumes oxygen to oxidize organic substances in the process of breathing, forming CO2 as a result.

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A widespread type of relationship that brings mutual benefits to the microorganism that interact is metabiosis, in which the life activity of certain microorganisms creates conditions for the development of others. Metabolic interrelations cause the sequence of transformations of some substances into others and underlie the cycle of substances in nature. An example of such relationships is the community of facultative and obligate anaerobes performing the process of fermenting sewage sludge in methane tanks, as well as nitrifying bacteria of the genera Nitrosomonas and Nitrobacter.

Finally, microorganisms often engage in the antagonistic relationship, which might be a crucial step for their survival. The antagonistic relationship between microorganisms is very diverse. This is predation (devouring of bacteria by the simplest microorganisms), and parasitism (the destruction of bacteria by bacteriophages), and the release into the environment of metabolic products that reduce the vital activity of other organisms or kill them (Cloud-Hansen et al, 2006). For example, the final product of the exchange of lactic acid bacteria – lactic acid – prevents the development of putrefactive bacteria. Some species of fungi and actinomycetes release into the environment biologically active substances – antibiotics, which have bactericidal action (Cloud & Hansen, 2006). Antagonism in the environment is one of the most important factors determining the composition of biocenoses.

It is also important to note that the composition and nature of biocenoses largely depends on the environmental conditions with which the life of microorganisms is inextricably linked. On one hand, the activity of microbes leads to significant changes in the environment as a result of the removal of nutrients from it and the release of metabolic products. On the other hand, the intensity of metabolic processes inside the cell largely depends on environmental conditions (factors). The environmental factors affecting the activity of microorganisms are divided into physical and chemical factors.

Physical factors. The most important physical factors that determine the activity of microorganisms include humidity, temperature, and light. For the active growth and development of microorganisms it is necessary to have water in the environemtn. Available form for them is water in a drip-liquid state. That is why the temperature range in which microorganisms can survive is limited to -2 ° C (or lower in media with high osmotic pressure) to + 100 ° C (Dworkin & Falkow, 2006).

Chemical factors. The concentration of hydrogen ions has a significant effect on the development of microorganisms. The majority of bacteria prefer a medium with a pH close to neutral (6.5-7.5) (Dworkin & Falkow, 2006). However, there are some types of bacteria that grow well in an alkaline or more acidic environment. A favorable environment for the development of fungi is a medium with a pH of 4-6, and actinomycetes grow better in an alkaline environment (Dworkin & Falkow, 2006).

In conclusion, interaction in various forms, including symbiosis and antagonistic relationship, is a crucial part of the survival and development of microorganisms.