Mutants of Paracoccidioides brasiliensis strain IVIC Pb9 affected in dimorphism.

Morphological mutants were isolated after nitrosoguanidine treatment of Paracoccidioides brasiliensis strain IVIC Pb9. Two of these mutants, Pb257 and Pb258, developed a typical mycelia at 23 degrees C, however, the yeast cells which developed at 37 degrees C were indistinguishable from those of the parental strain. A third mutant, strain Pb267, was thermosensitive, grew as yeast-like cells at 23 degrees C, but was unable to survive at 37 degrees C. Morphological observations as well as serological and segregation tests confirmed that the mutant strains originated from P. brasiliensis. Cell wall chemical analyses of the mutant strains grown at 23 degrees C indicated the presence of alkali-soluble, acid-insoluble polysaccharides absent in the parental wild-type strain Pb9 grown under the same conditions. The phenotypes shown by the mutant strains may be related to deficiencies in the proper synthesis of cell wall components of the mycelial phase of this fungus.