Isolation of sexual strains of Chlamydomonas

SUMMARY: The zygospores of several species of Chlamydomonas present in dry soil are very resistant to dehydrating agents. Based on this resistance a method for the isolation of sexual strains has been developed, and two homothallic and three heterothallic species of Chlamydomonas have been obtained in pure culture. A unicellular green alga which can grow without difficulty in pure culture, and which can be induced to undergo a complete sexual life cycle under experi-mental conditions, would offer possibilities as a suitable organism for an attack on problems in biochemical genetics for which Neurospora and similar heterotrophs are unsuited. Mating strains of a few species of Chlamydomonas have been isolated (Moewus, 1933; Gerloff, 1940; Smith, 1946; Bold, 1949; Lewin, 1949), but for various reasons none has proved altogether satisfactory. Several workers experienced difficulty in obtaining sexual strains when random isolates of Chlamydomonas from soil were paired and examined for mating reactions, Schreiber (1925) reported a lack of success when as many as 70 clones were tested in this way. An easier method was therefore sought an