New data on physiological and morphological characteristics of Acidomyces acidothermus (Teratosphaeriaceae, Ascomycota) based on a study of strains from thermal sites of the Avachinsky Volcano (Kamchatka Territory, Russia)

Three isolates of Acidomyces acidothermus was obtained from volcanic substrates at the Avachinsky Volcano (Kamchatka Territory), where it was the dominant species. Strains (NN-417, NN-433, and NN-436) were identified based on phylogenetic analysis of the ITS1-ITS4 rDNA region; their morphology and physiology were also studied. The species A. acidothermus was previously isolated from extreme acidic and thermal habitats in the Czech Republic, Iceland, Japan, and Vietnam. The representative strain of A. acidothermus NN-433 is an obligate acidophile; under laboratory conditions, it grows in an acidic media but is unable to grow at a pH above 7. The strain is thermotolerant and has a low tolerance for osmotic stress. These limits are narrower than those of the type strain from Japan or the European strains from the Czech Republic and Iceland, which suggests local adaptation. For the first time in the genus Acidomyces, we describe pycnidium-like structures containing dark, spherical, unicellular conidia. These findings reveal a previously unknown reproductive strategy for the genus, as well as significant intraspecific physiological variability in A. acidothermus.