A NEW CLASS OF ARGININE-REQUIRING MUTANTS IN CHLAMYDOMONAS REINHARDI

Forward mutations to auxotrophy have been induced in Chlamydomonas reinhardi after treatment of wild-type cells with ethyl methanesulfonate (EMS) and plating on a selective medium supplemented with yeast extract but deprived of ammonium chloride. Among the 41 stable mutants isolated, 6 were arginine-requiring. Reconstruction experiments show that the growth of all these arginine auxotrophs is inhibited on media containing high concentrations of NH4+ions. It is concluded that the isolation of this new class of mutants was made possible because of the low ammonium concentration of the plating medium. It appears therefore that in Chlamydomonas, as in other microorganisms, the specificity of mutations may be imposed by the selective medium. © 1969 Springer-Verlag.