Antagonism in Biology

a phenomenon reflected primarily in the struggle for existence. Antagonistic relations can be traced most clearly between a predator and its prey (predation) and between a parasite and its host (parasitism). Antagonism also applies to competitive relations (competition)—for example, competition for light or mineral nutrition among plants and for the same food among animals.

In physiology, similar relations, called antagonism of physiological functions, also occur in the activity of skeletal muscles; in some functions of the sympathetic and parasympathetic parts of the autonomic nervous system acting in opposition to the pupil, cardiac acitivty, and so on; and in the activity of the nervous system with its two active nerve processes, excitation and inhibition, which constitute a unity of opposites. Antagonism of functions and of regulatory influences is the basis not only of neural reflex regulation but also of humoral, hormonal, and neurohumoral regulation which keep such vital constants as blood pressure and osmotic pressure of blood at a constant level (homeostasis).

Antagonism of ions, drugs, and poisons is manifested by the loss of the particular substance’s toxic or therapeutic (useful) action when injected into the body in combination with another substance—a drug or poison.

Antagonism of microorganisms (also antibiosis), the suppression of some species of microorganisms by others. First observed by L. Pasteur in 1877, it occurs frequently in nature. Under the influence of antagonists, microorganisms cease to grow and reproduce in some cases, their cells lyse or dissolve in other cases, or such biochemical processes within the cells as respiration and synthesis of amino acids become inhibited or cease in still other cases. Antagonism is most pronounced among actinomycetes, bacteria, and fungi. Pseudomonas aeruginosa actively suppresses the plague microorganism. Actinomycetes, which produce nystatin, inhibit the growth of yeasts. Antagonism is also observed among algae and protozoa. The mechanism of antagonism is varied and often obscure. Antagonists more often than not act on their competitors with metabolic products (allelopathy), including antibiotics, or displace the competitors by means of more intensive reproduction or primary utilization of food. Repeated attempts were made as early as the 19th century by V. A. Manassein (1871), A. G. Polotebnov (1872), and others to treat diseases caused by bacteria; however, these attempts were unsuccessful because of the use of unpurified preparations. Microbial antagonists are extensively used in the production of antibiotics. Antagonists greatly influence soil fertility. By developing luxuriantly in the soil, useful microbial antagonists inhibit the growth of many phytopathogenic bacteria and fungi, thereby sanitizing the soil. Antagonists can be used in many branches of the food industry.