Several growth conditions were found to allow abundant arthrospore formation in T. mentagrophytes. These included growth at 32--37 degrees C on Sabouraud's medium (1% neopeptone, 4% glucose) and growth at temperatures below 32 degrees C solely on neopeptone or other complex peptide sources without the addition of glucose, a supplementary carbon source. Sabouraud's medium did not allow arthropsore formation at 30 degrees C under normal atmospheric conditions. However, if oxygen tension were reduced by partial replacement of air with either N2 or CO2 arthrosporulation did occur on Sabouraud's medium at 30 degrees C. The rate of germ tube elongation was lower under those conditions which supported arthrospore formation, suggesting a correlation between decreased rate of hyphal extension and arthrospore formation. Stimulation of arthrospore formation by sublethal concentrations of several antifungal agents tends to support this hypothesis.

The effect of intracellular trehalose and glycogen on the survival of spores of Dictyostelium discoideum ATCC 25697 after exposure to supraoptimal temperatures was examined. Cells metabolically perturbed by incubation in glucose and inorganic phosphate have intracellular trehalose and glycogen concentrations fivefold and twofold higher, respectively, than those of the controls. These cells were more resistant to the lethal effects of wet heat (45 degrees to 55 degrees C) than were control cells. The presence of 40 mM trehalose in the buffer during heat stress increased the survival of nonperturbed cells to approximately the level of the perturbed cells. No protection was observed when cells were heated in the presence of exogenous glycogen. Glucose or disaccharides other than trehalose when present during heat stress, had no effect on heat resistance. Nonperturbed cells preincubated in 40 mM trehalose and washed before heat stress were more resistant to killing than were controls. Cells perturbed with inorganic phosphate, which has been shown to increase trehalose concentrations but decrease glycogen concentrations, were also more resistant to the lethal effects of wet heat than were controls. The data suggest that trehalose has an effect on the wet-heat resistance of D. discoideum. Some possible mechanisms are suggested.

The formation of arthroconidia, especially the ontogeny of the arthroconidial wall in the dermatophyte Trichophyton mentagrophytes, was investigated by light and electron microscopy. Time-lapse photomicroscopy revealed that the new septa were inserted regularly along the length of the hypha. Each new septum divided a preexisting hyphal segment into approximately equal halves. The initial sign of arthroconidium formation detected by electron microscopy was the deposition of a conidium-specific wall layer on the inner surface of the preexisting hyphal wall. The invaginating septal material was continuous with the newly deposited inner wall layer of the sporulating hyphae. When septation was completed, the septum and septal furrow were continuous across the wall to the inner edge of the outer wall layer. After septation, the inner wall continued to thicken until it attained the thickness of a mature arthroconidial wall (0.3 – 0.5 μm). Simultaneously, immature arthroconidia continued to swell and eventually assumed a barrel shape. When disarticulated, arthroconidia were surrounded by the newly formed conidial wall at the poles, and the sides of the conidia were additionally bounded by the residual hyphal wall. As the arthroconidia matured, the remnants of the hyphal wall tended to be detached from the spore surface. From these observations we conclude that T. mentagrophytes formed arthroconidia by the enteroarthric mode rather than the holoarthric process as previously described.

Examination of immune complexes between cells of Streptococcus mutans and homologous antiserum by the techniques of thin-sectioning and freeze-etching revealed that the cells were embedded within and extensive matrix 80-90 nm thick with defined boundaries.

Malate dehydrogenase (MDH; EC 1.1.1.37) from Dictyostelium discoideum was purified and characterized MDH activity from whole cells was purified 275-fold. The mitochondrial and cytoplasmic MDH present co-purified through three ion exchange and affinity chromatography steps. The isoenzymes were barely separable by either disc gel electrophoresis or isoelectric focusing. The purified preparation containing both isoenzymes had a single pH optimum (9.3-9.5) and an apparent molecular weight of 70000. It exhibited linear kinetics and responded to known inhibitors of MDH, i.e. thyroxine and hydroxymalonate. Michaelis and dissociation constants obtained with this preparation were similar to those obtained with a 10-fold purified mitochondrial MDH.