Abstract
Paradana is one of the biggest ice caves in Slovenia, with an estimated ice volume of 8,000 m3. Reflecting climatological conditions, the cave ice undergoes repeated freeze-thaw cycles and regular yearly deposition of fresh ice. Three distinct ice block samples, collected from the frozen lake in May 2016, were analysed to obtain data on ice physicochemical properties and the composition of associated microbiota. Isotopic composition of the ice samples (18O, 2H) and a local meteoric water line (LMWL) constructed for monthly precipitation at Postojna were used to estimate the isotopic composition of the water that formed the ice, which had high values of deuterium excess and low concentrations of chloride, sulphate and nitrate. The values of total organic carbon (1.93–3.95 mg/l) within the ice blocks fall within the range of those measured in karst streams. Total cell count in the ice was high and the proportion of cell viability increased along the depth gradient and ranged from 4.67 × 104 to 1.52 × 105 cells/ml and from 51.0 to 85.4%, respectively. Proteobacteria represented the core of the cave-ice microbiome (55.9–79.1%), and probably play an essential role in this ecosystem. Actinobacteria was the second most abundant phylum (12.0–31.4%), followed in abundance by Bacteroidetes (2.8–4.3%). Ice phylotypes recorded amounted to 442 genera, but only 43 genera had abundances greater than 0.5%. Most abundant were Pseudomonas, a well-known ice dweller, and Lysobacter, which previously was not reported in this context. Finally, two xanthophytes, Chloridella glacialis and Ellipsoidion perminimum, known from polar environments, were cultured from the ice. This indicates that the abundance and ecological role of phototrophs in such environments might be greater than previously deduced.
Highlights
Cold ecosystems include deep oceans, polar regions, high mountains and subterranean caves with a large variety of aquatic and terrestrial e cosystems[1]
Physicochemical analyses of individual ice blocks were conducted to observe eventual differences that could be attributed to spatially related gradual freezing–melting and fresh ice deposition, and to characterize the habitat that enables long-term survival of ice microbiota
All ice samples contained low concentrations of salts, indicating that they originated from recent clean snow
Summary
Cold ecosystems include deep oceans, polar regions, high mountains and subterranean caves with a large variety of aquatic and terrestrial e cosystems[1]. Even if the study of these habitats is supported strongly by the rapid development of new technologies (which shed more light on the gene presence, functional gene potential, gene expression, in situ identification of active microorganisms and biotechnological potential) more fundamental ecological research is needed urgently In this respect there is a lack of information on the dynamics and functions of microbial communities, their management and predictive models, interactions between micro- and macroorganisms in cold habitats, linkage of biodiversity, climate, and function and an integrated view encompassing micro- and macroorganisms and the physical e nvironment[1]. The detail of cave-ice deposition is largely impacted by snow levels, the presence of external organic debris, the influence of cave percolation water, and the effects of strong air circulation Such extreme environmental conditions could direct the compartmentalization of microbial habitats
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