Microbial Communities in Natural Mineral Waters of Bulgaria: Diversity and Biotechnological Potential

Mineral waters represent unique limnological ecosystems with stable physicochemical conditions and specialised microbial communities adapted to extreme environments. Bulgarian mineral waters remain comparatively underexplored despite their considerable ecological and biotechnological significance. This review analyses current knowledge on the diversity, ecological functions, and biotechnological potential of microbial communities from Bulgarian mineral springs. A comprehensive literature survey covers studies published between 1990 and 2026. The study integrates hydrogeological, limnological, microbiological, and biotechnological data and encompasses both culture-dependent methods and molecular approaches. The available evidence demonstrates that microbial communities in Bulgarian mineral waters include diverse bacteria, archaea, cyanobacteria, microalgae that adapt to broad thermal and geochemical gradients. These microorganisms actively participate in element cycles, form complex biofilms, and show numerous physiological adaptations to oligotrophic and extreme conditions. Many taxa produce thermostable enzymes, antimicrobial compounds, exopolysaccharides with potential applications in medicine, industrial biotechnology, environmental remediation, and cosmeceutical technologies. The review identifies significant research gaps and emphasises the importance of integrated multi-omics approaches for future exploration of Bulgarian mineral water ecosystems.