Radioactive Springs and Archaeal Life in Deep Groundwater Systems

This study investigates the archaeal lipid distribution in freshwater springs with a particular focus on lipidomic profiles as ecological indicaters. Cultivation-independent approaches were employed to analyze organisms that had not yet been cultivated in the laboratory. Shotgun lipidomics of 21 springs in western and central part of Slovakia revealed more than 100 characteristic archaeal lipids, from which three biomarker groups were selected: (i) core lipids containing archaeol and glycerol dialkyl glycerol tetraethers (GDGT), including their mono and dihydroxy derivatives; (ii) mono- to tetra-glycosides of archaeol and GDGTs; and (iii) six phosphoarchaeols (archaeol-based phospholipids). Statistical analyses classified springs into three categories: cold (temperature < 20 °C), warm (> 30 °C), and radioactive (a subset of cold springs with ˃100 Bq/L radioactivity). Significant shifts in the ratios of archaeal lipids were correlated with the temperature and radioactivity, demonstrating the sensitivity of lipidomic profiling to environmental parameters. Moreover, tandem mass spectrometry identified a previously undescribed metabolite, archaeol-based dimethylphosphatidylethanolamine. The applied method provides rapid and highly sensitive tools for screening the presence of archaea, detecting as few as several thousand cells per liter, and offers new insights into the ecology of archaeal communities in groundwater environments.