GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

21. MICROORGANISMS AND THE ENVIRONMENT

21.3. TYPES OF INTERSPECIFIC INTERACTIONS AMONG ORGANISMS IN NATURE

21.3.2. Antagonistic interactions

Antagonistic interactions manifest as the inhibition of one or more members of a microbial community by others.

Passive (competitive) antagonism refers to interactions in which different microorganisms utilize the same nutrient resources. Passive antagonism is essentially competition in the struggle for nutrients and living space. In this struggle, an advantage is held by microorganisms characterized by high growth rates and undemanding nutritional requirements.

Active antagonism is driven by the secretion of bactericidal substances. These may include non-specific metabolic byproducts (organic acids, alcohols, ammonia, phenols, etc.) that cause the coagulation of cytoplasmic Proteins. For instance, lactic acid Bacteria acidify the medium, thereby suppressing the growth of putrefactive bacteria. Another cause of active antagonism is The production of specific bacteriostatic or bactericidal substances—Antibiotics—which act selectively on other microorganisms. The form of antagonism mediated by antibiotic synthesis is known as antibiosis. In 1928–1929, A. Fleming observed the pronounced inhibition of pathogenic staphylococci by the fungus Penicillium notatum. In 1941–1942, E. Chain and H.W. Florey isolated the antibiotic penicillin from the fungal culture broth. For this discovery, which marked the dawn of a new era in The history of medicine—the antibiotic era—A. Fleming, E. Chain, and H.W. Florey were awarded the Nobel Prize.

The phenomenon of microbial antagonism is widely utilized in medicine and agriculture. Living microorganisms are employed to combat dysbiosis, treat and prevent infectious diseases, prevent the proliferation of toxin-producing Fungi in animal feed, and control phytopathogenic microorganisms.

Antagonistic interactions are most vividly expressed in the forms of parasitism and predation. Drawing a sharp distinction between these forms of interaction is difficult, as both predators and parasites satisfy their nutritional requirements at the expense of a host. The difference lies in the fact that predators kill their prey immediately, whereas parasites derive sustenance from a living Organism that remains alive for an extended period. For example, Bacteriophages (bacterial Viruses) are obligate parasites; they have lost the capacity for a saprophytic lifestyle, as they cannot reproduce outside a host organism. Bacteria of the genus Bdellovibrio are parasites of Gram-negative bacteria. Facultative parasites are capable of developing outside the host organism and can even grow on nutrient media.

Thus, specific relationships are established among microorganisms within natural associations; these relationships are dynamic and lack rigid boundaries. The factors that determine the manifestation of particular forms of interaction depend on specific environmental conditions as well as the unique metabolic CHARACTERISTICS OF THE organisms themselves.