Cultivation and properties of Echinamoeba thermarum n. sp., an extremely thermophilic amoeba thriving in hot springs.

Here we describe a new, extremely thermophilic amoeba growing between 33 degrees C and 57 degrees C ( Topt.=50 degrees C). Isolates had been obtained from hot springs at Agnano Terme (Italy), Yellowstone National Park (USA), Kamchatka (Russia), and the Arenal Volcano (Costa Rica). They could be cultured monoxenically on a thermophilic alpha-proteobacterium. The morphology of the amoeba was studied using a microscope situated under a heatable polyacrylate hood. At 50 degrees C, the cells appeared flat with an irregular triangular or elongate shape, sometimes exhibiting fine spine-like subpseudopodia. On average, they were 22 microm long and 11 microm wide and had one nucleus with a central nucleolus. Based on morphology and on SSU rRNA comparisons, the amoeba belonged to the genus Echinamoeba, where it represents a new species. Referring to its extremely thermophilic lifestyle and its hydrothermal habitat, we name it E. thermarum.