Hranice Karst is situated in northeastern part of Moravia, Czech Republic, at the contact between two major geological units of the Bohemian Massif and Western Carpathians. This karst developed in combination of meteoric water and hydrothermal dissolution of deformed and tectonically stacked Devonian and Lower Carboniferous limestones. This karst, therefore, exceeds to considerable depths of several hundreds metres. In the 1977, unusually massive organic coatings high in microbial extracellular polymers, occurring together with biofilm structures, were discovered in the vertical caves of low hydrothermally active ‚Hranická propast (Hranice Abyss)‘, particularly on the cave walls in deep underwater environments. These mucilaginous formations may have been classified among ‚snottites‘, mucous-like coatings and stalactites. The present study provides the first insights into both the microbial diversity and morphological/structural variability of these extremophilic formations.Hranice Karst is situated in northeastern part of Moravia, Czech Republic, at the contact between two major geological units of the Bohemian Massif and Western Carpathians. This karst developed in combination of meteoric water and hydrothermal dissolution of deformed and tectonically stacked Devonian and Lower Carboniferous limestones. This karst, therefore, exceeds to considerable depths of several hundreds metres. In the 1977, unusually massive organic coatings high in microbial extracellular polymers, occurring together with biofilm structures, were discovered in the vertical caves of low hydrothermally active ‚Hranická propast (Hranice Abyss)‘, particularly on the cave walls in deep underwater environments. These mucilaginous formations may have been classified among ‚snottites‘, mucous-like coatings and stalactites. The present study provides the first insights into both the microbial diversity and morphological/structural variability of these extremophilic formations
