Identification and Characterization of Variants of Crithidia luciliae with Altered Morphological and Surface Properties

ABSTRACT. Variants of a cloned laboratory stock of the trypanosomatid parasite Crithidia luciliae have been distinguished from “parental type” organisms. These variants accumulated spontaneously over time as the protozoan was maintained by continuous passage in a chemically defined medium. Cloned lines of these variants have been isolated by plating on nutrient agar and partially characterized on the basis of their growth characteristics in culture, their colony and cellular morphology as well as their surface protein expression. One cloned line consisted of motile, flagellated forms which, unlike “parental type” organisms, did not adhere to the surface of culture flasks. Another cloned line was composed of non‐adherent, nonmotile, amastigote‐like forms which were further distinguished from “parental type” cells by virtue of their constitutive expression, in nutrient‐replete medium, of high levels of a surface membrane associated 3′‐nucleotidase/nuclease (3′‐N'ase) activity. Both the motile, flagellated and amastigote‐like variants, like the “parental type” organisms, exhibited elevated levels of the 3′‐N'ase activity upon exposure to purine starvation conditions. The variants described are of potential importance in elucidating the mechanism of induction of the highly regulated 3′‐N'ase activity as well as for understanding the cytoskeletal systems and the surface properties of these protozoa.