Morphology of slime variants of Neurospora crassa growing on a glass surface in liquid medium

Abstract

Two Neurospora crassa strains designated slime, FGSC no. 1118 and 326, were observed during their growth on glass surfaces in liquid medium by phase contrast microscopy, and following fixation, dehydration and critical point drying, by scanning electron microscopy. Both strains were found to grow by several processes:

• 1. Production of microhyphae with terminal bulbs which often contained nuclei and could change into spheroplasts once the subapical microhyphal stalk was severed.

• 2. Amoeboid movement of large flattened spheroplasts extended on the glass surface like a pancake, followed by pinching off of beaded spheroplasts from extended flattened spheroplasts. A number of different drugs caused rapid bead formation from flattened spheroplasts. These included inhibitors known to cause disaggreation of cytoplasmic microfilaments such as cytochalasins A and B, inhibitors of respiration and oxidative phosphorylation such as azide, cyanide, dinitrophenol, phenazinemethosulfate, antimycin A, and arsenate, and ion carriers and ions such as carbonyl cyanide m-chlorophenylhydrazone, potassium chloride (0.15 M), ethylenediaminetetraacetate, and sodium pyrophosphate. Similar effects were observed after application of reagents affecting cyclic nucleotides such as dibutyryl cyclic adenosine-3:5-monophosphate and caffeine, and sulfhydryl reagents such as N-ethylmaleimide, iodoacetate, p-chloromercuribenzoate.Cyanide treatment resulted in a biphasic response: initially bead formation, followed by retraction of protoplasm of peripheral beads into a central large spheroplast. The second phase may require energy from glycolysis since it was inhibited by fluoride. The pretreatment of spheroplasts by concanavalin A prevented this change in every case, probably because of a cross-linking of membrane components.

  The rapid contraction and movement of these cells is consistent with the presence of contractile proteins similar to actin and myosin in Slime and suggests a search for such proteins in Neurospora. During growth of slime 1118, wall-like material accumulated in the medium. Such material was isolated and found to contain protein (51.5%); polysaccharides appearedto be the major form-giving component. This dried powdered wall-like material also contained 11–15 μg of lipid phosphorus per mg. A 10 min 3/4 inch television cassette offering time lapse photographic sequences of the processes described is available from the authors.