RESUMO
A novel acidophilic fungal strain isolated from snottites in the active sulfuric acid speleogenesis (SAS) Sheki-Heh Cave (North Caucasus, Chechen Republic) was identified and characterized. The Sheki-Heh Cave is one of three cavities of the joint SAS speleosystem; to date, it remains the only of such cave explored in Russia. Highly acidic biofilms termed snottites are found sporadically on the cave roof in sulfurous water degassing zones. Only dark-colored micromycete colonies were isolated from these microbial biofilms using direct inoculation onto Czapek agar. The dominant fungal isolate was selected for further characterization. This work aimed to identify the micromycete strain isolated from cave snottites and explore its growth characteristics. Based on the phylogenetic analysis of the rDNA ITS region (540 bp), the novel fungal strain was identified as Acidomyces acidophilum with a similarity level of 99.26%. The physiological properties of the strain were examined; the optimal pH and temperature for its growth were pH 3 and 20-28 °C, respectively. Strain IB-G85 is able to grow under NaCl concentrations up to 3%. Although IB-G85 was isolated from an oligotrophic environment and was growing under nutrient deficiency, it could utilize some sugars and proteins as well as recalcitrant substrates, such as chitin and tannin. Compared to base Czapek-Dox Agar, lactic acid and colloidal chitin as the sole carbon sources enhanced fungal growth by 100 and 59%, respectively. The occurrence of A. acidophilum and closely related fungal species within acidophilic microbial communities inhabiting sulfur-containing ecosystems is discussed in view of their contribution to snottite structure formation in SAS caves.
