Effects of cell wall deficiency in 'slime'strains of Neurospora crassa: a study on mycelial and wall-less phenotypic derivatives of a single fz; sg; os-1 ('slime'-like) segregant

Some morphological, physiological, enzymic and genetic characteristics of mycelial and plasmodioid phenotypes of Neurospora crassa, obtained by vegetative selection of a single fz; sg; os-1 (‘slime’-like) segregant of a cross ‘slime’ × wild-type, were studied. The mycelial phenotype of the segregant, albeit altered in morphology, was otherwise fully normal for export and regulation of invertase and β-glucosidase. In contrast, both enzymes were oversecreted and were resistant to catabolic regulation in the stable ‘slime’ phenotype, derived from the same isolate. These results suggested that the enzymic defects of ‘slime’ appeared gradually, concomitantly with the loss of ability to construct a cell wall, as a consequence of the process of vegetative selection required to produce stable ‘slime’ from mycelium-forming ‘slime’-like segregants. This idea was reinforced by the isolation of an intermediate phenotype, which exhibited mycelial/spheroplast dimorphism conditioned by the osmolarity of the culture medium. Crosses of the two extreme phenotypes of the fz; sg; os-1 segregant (the mycelial and the stable ‘slime’) failed to demonstrate any significant genetic difference between them.