Microbial Distribution in Nature
Microbes are ubiquitous in nature, being distributed everywhere. They are found in the soil, water, air, in plants, animals, foodstuffs, various utensils, within human body and upon human skin or mucosal membranes.
Microbial ecology (Gk oikos – home, logos – science) studies substantial complex relationships that connect microbial populations with their environment.
All of microorganisms inhabiting a certain area or body compartment are regarded as microbial community.
Biotope means the place of habitation of the certain microbial population.
Microbial community, biotope and their multiple specific interrelationships form ecosystem.
The role that an organism plays in its particular ecosystem as well as the physical space it occupies is termed as microbial ecological niche.
Ecovariant is the isolate of a certain microorganism adapted for the habitation within definite ecological system. Among various microbial isolates hospital ecovariants (or hospital strains) are of great medical importance. Their ecological niche is formed in hospitals and clinics, so these strains are extremely resistant to many antibiotics and other antimicrobial drugs. They cannot be eliminated readily.
The study of microbial ecology creates the proper basis, which allows to get insights into the mechanisms of microbial parasitism as well as to elaborate the measures for the control of various infectious diseases.
There are certain common types of relationships among the microbes maintained within their microbial communities.
Long-term cooperative interactions established between microbial species are called symbiotic, competitive – antagonistic.
Symbiosis includes the diverse microbial interrelationships.
Neutralism means the mode of relations, where the bacteria don’t influence each other within microbial community.
Commensalism is the kind of symbiosis, where one species exploits another without harmful effect. Commensal bacteria are normal inhabitants of human body.
Mutualism is the beneficial co-existence of two or more species. For instance, nitrogen-fixing root nodule bacteria from Rhizobium genus live together with some leguminous species.
Synergism means intensifying of functions of bacteria during mutual cultivation or dwelling. In such a situation the cooperation of non-pathogenic and pathogenic bacterial species may lead to the emergence of infectious process. As an example, acute necrotizing gingivitis arises from the complex polymicrobial infection of oral cavity, which major causative agents are oral spirochetes and gram-negative anaerobic Prevotella intermedia species.
Satellitism is observed, when the by-products of one bacterial species activate the propagation of another microbial species (microbial cross-feeding). For instance, vitamins and growth factors produced by the yeasts stimulate the growth of Bordetella pertussis.
Parasitism is the complex of microbial interplays, where one organism exploits another with the harmful effect for the latter. Typical parasites are bacteriophages – the viruses, affecting bacterial cells.
Similarly, competitive antagonistic relationships are also observed in any kind of complex microbial coexistence. As the result of their practical use, in biotechnology antagonistic bacteria are thoroughly selected and used for synthesis of antibiotics.
There are three main forms of antagonism: overt, forced and violent.
In case of overt antagonism the microbe-antagonist produces antibiotics independently on rival presence.
In situation of forced antagonism antibiotic production by some microbial population is triggered only if the rival appears within the biotope.
And violent antagonism is characterized by the fact that both competitors don’t produce antibiotics, but in conditions of poor cultivation one species uses another as the source of nutrition.
Mechanisms of antagonism include antibiotic synthesis, production of bacteriocins, exhaustion of nutrient media, acceleration of the rate of metabolism, pH and pO2 changes, etc.