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

Abstract

Here we describe a new, extremely thermophilic amoeba growing between 33 °C and 57 °C (T _opt. = 50 °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 °C, the cells appeared flat with an irregular triangular or elongate shape, sometimes exhibiting fine spine-like subpseudopodia. On average, they were 22 μm long and 11 μm 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.