Temperature tolerance of pathogenic and nonpathogenic free-living amoebas

Within tested strains of the genera Naegleria and Acanthamoeba the ability to grow at high temperatures seems directly related to virulence, with nonvirulent strains unable to grow at normal or elevated body temperatures. Outside these genera, nonvirulent Hartmannella and Tetramitus do grow at elevated temperatures, which suggests a barrier to pathogenicity other than temperature sensitivity. The high optimal temperature of pathogenic Naegleria apparently explains previous difficulty in obtaining isolates from the aquatic environment.

Development of cellular dependence on infective organisms: micrurgical studies in amoebas

Nuclei and cytoplasm were transferred between a normal strain anda variant strain of Amoeba discoides heavily infected with bacteria. After 5 years of infection, the infective bacteria that were initially harmful to the host cells became harmless, and the nucleus of the host cell became dependent on the infective organisms for its normal functions.

[Enrichment and characterization of a bacteriolytic amoebic enzyme]

Extracts of cultures of a small free-living amoeba, which feeds mainly on gram-negative bacteria, are capable of lysing heat-killed gram-negative bacteria. The lytic activity was enriched 36-fold by means of precipitation with (NH4)2SO4 and of chromatography on Sephadex G-75, followed by ultrafiltration. The activity is less resistant to heat than is lysozyme, and is optimal at 45°C. The pH-optimum is at 6.5. The molecular weight corresponds to that of lysozyme from chicken eggwhite; the isoelecric point is at 10.0. The effect of the amoebic activity on cells of A. metalcaligenes and M. lysodeikticus is different from that of eggwhite lysozyme on the same cells. We conclude that the lytic activity of the amoeba is due to a lysozyme with a special mode of action.

Alternative developmental pathways determined by environmental conditions in the cellular slime mold Dictyostelium discoideum

The cellular slime mold Dictyostelium discoideum grows in the soil as a population of independent, uninucleate amoebae. Upon entrance to the stationary phase, the amoebae collect in multicellular aggregates to form organized fruiting bodies composed of spores and stalk cells. Depending upon environmental conditions, the developing aggregate either constructs the fruiting body at the site of aggregation or transforms into a structure that can migrate to a more favorable location. Environmental conditions that favor migration are (i) the accumulation of metabolite(s) produced by the aggregate and (ii) a low ionic strength in the substratum. Conditions that prevent migration or that stop a migrating slug are (i) the presence of buffer and (ii) illumination by overhead light.