Slime, the wall-less variant of Neurospora crassa: The loss of cell-wall assembly is not due to the loss of cell-wall primer or template

Abstract

The cell wall-less variant of Neurospora crassa, slime, when initially recovered from a mycelial heterokaryon, grows as a mixed population of protoplasts and cells which contain a partial or incomplete wall (hyphlet cells). After prolonged, daily growth and filtration through glass wool, cultures consist exclusively of protoplasts which lack cell surface-bound, wall-like material; these cells are not capable of forming sexual and asexual fusions with mycelial strains, slime protoplasts and protoplasts from a temperature-sensitive osmotic-1 strain were fused using polyethylene glycol and the resulting heterokaryons were allowed to regenerate a mycelium. slime homokaryons were re-isolated from several mycelial heterokaryons and were not able to form sexual and asexual fusions; populations of cells were comprised exclusively of protoplasts. Thus, the loss of a slime culture's ability to form a partial cell wall is not likely to be due to an epigenetic phenonemon but may be due to selection of cells that bear additional mutations.