Concerning Pattern Formation by Free-Swimming Microorganisms

The action of several agents and conditions upon the pattern formation observed in cultures of motile microorganisms has been studied using protozoa, viz., Tetrabymena pyriformis. A general description of the macroscopic and microscopic characteristics of the pattern and of its formation and organization was given. It was shown to be dependent upon both concentration of ciliates and the depth of the suspension. Hydrogen-ion concentration, per se, had no influence. Anything which decreases motility, e.g., low temperature, high osmotic pressure, anaerobic conditions, ultraviolet radiation, Parathion, methyl cellulose and advanced age, directly decreases the rate of pattern formation, and the sharpness of its facets once formed. Once the number of motile cells in a culture falls below the critical concentration, it will no longer form a pattern.