Development of Resistance to Pyrithiamine in Yeast and Some Observations on Its Nature.

Summary

A strain of Endomyces vernalis was obtained by growing the yeast in media containing pyrithiamine. This strain was not affected in growth by concentrations of pyrithiamine 25 times greater than that required to inhibit the growth of the parent strain halfmaximally. The new strain still required thiamine or its pyrimidine portion as a growth factor. In the absence of thiamine, pyrithiamine was 50% as active as the vitamin for growth of the variant. When grown in small concentrations of pyrithiamine and in the absence of thiamine, the new strain converted half of the pyrithiamine to the pyrimidine portion of thiamine.