Cyanobacterial diversity of five selected thermal springs in Serbia

Thermal springs, with their specific physico-chemical features, represent a unique and dynamic environment and are habitats for diverse and special forms of organisms. These habitats are potential sources of interesting taxa, particularly Cyanobacteria, which are crucial for understanding certain ecological and evolutionary processes, of which some may have potential biotechnological applications. Five thermal springs in central Serbia (Bukovička Spa, Vrujci Spa, Omoljica, Poljane and Ovčanska Spa) were visited in November and December 2023. Selected water parameters were measured on site (temperature, pH, conductivity, oxygen content, total dissolved solids), while chemical analyses were carried out in the laboratory. Phototrophic biofilms were collected at sites of water discharge, sites moistened by thermal water, sediments and mud. Cyanobacteria were examined optically and were cultivated so that they could later be evaluated by means of molecular analyses. Representatives from over 15 genera of Cyanobacteria were identified. In Bukovička and Vrujci Spa, most of the biofilm samples were collected from water-wetted sites at drinking fountains and were characterised by the presence of numerous coccoid representatives (e.g., genera Aphanocapsa, Chroococcidiopsis, Gloeocapsa, Synechococcus). Biofilm samples from other localities were mostly from thermal water overflow sites and were generally dominated by simple trichal cyanobacterial forms, most of which belonged to the genus Phormidium, but also Jaaginema, Leptolyngbya and Oscillatoria. Interesting representatives of simple trichal cyanobacteria were found in Poljane, characterised by unusual morphological features and the presence of yellow and black granules on their surface. Thermal springs in Serbia are still little explored places where potentially rare species can be found, so more attention should be paid to them.