The Culture and Division Rate of Dileptus gigas

Abstract

Although pedigree isolation cultures of protozoa have been carried on during the last 50 years, relatively few investigators have experimented with carnivorous forms. Woodruff and Spencer 1 and Woodruff and Moore 2 kept Spathidium spathula alive for long periods without degeneration, conjugation or endomixis on a diet of Colpidium colpoda. Beers, 3 feeding Didinium nasutum on Para-mecium caudatum succeeded in attaining 1384 generations in about a year's time, without any degeneration or internal reorganization of any kind. With these results in mind it was decided to attempt to find a suitable diet for the carnivorous ciliate, Dileptus gigas, and to ascertain its division rate on such diet in isolation pedigree cultures.

In 1936 a number of individuals of Dileptus gigas were isolated from some of the writer's stock cultures. These cultures were originally collected from Van Cortlandt Park Pond, New York. By preliminary feeding experiments it was soon ascertained that the large, blue Stentor coeruleus made an excellent food basis for Dileptus and this readily cultured organism 4 was therefore selected as the standard food supply for the experiment. Visscher 5 has described the interesting and unusual manner in which Dileptus manages to attack, paralyze, and cytolyze by means of the powerful trichocysts (toxicysts), stentors much larger than itself and feast upon its prey. It is interesting to add that Stentor, itself predominantly carnivorous, was grown on Belepharisma undulans, 4 the latter being supplied with a mixed diet.

On Nov. 21, 1936, two series, consisting of 4 pure lines each, were established. All of these 8 lines were the progeny of a single Dileptus isolated from stock culture on Nov. 18. The organisms were kept in Maximow culture dishes in a moist chamber and were isolated daily (occasionally every other day) by capillary pipette under a binocular dissecting microscope.