Cyanobacteria and algae from biofilm at the entrance zone of Petnica Cave

The importance of biofilms in caves, the diversity of microorganisms in them, their mutual relationship and relationship with the substratum are among the advancing research topics in microbial biospeleology. This research is making contribution to the knowledge about biofilms at cave entrances and phototrophic communities in them. In that manner, biofilms from the entrance zone of the Petnica Cave were examined. Light microscopy showed that cyanobacteria were exclusively dominant phototrophs (34 taxa out of 39 total taxa recorded) with coccoid forms prevailing (28 taxa); simple trichal forms were present to a lesser extent, while heterocytous ones were completely absent. Genera Gloeocapsa, Chroococcus,Gloeothece and Leptolyngbya were the most diverse. Four green algal genera characteristic for aerophytic habitats (Apatococcus, Desmococcus, Haematococcus and Trentepohlia) were also recorded, while Bacillariophytawere observed sporadically. Three groups of sampling sites were distinguished based on recorded taxa, their richness and similarity, using non-metric multidimensional scaling (NMDS). Quantitative biofilm characteristics were also assessed - the content of chlorophyll a (Chl a) was determined, as well as the contents of water, organic and inorganic matter. Chl a had a significant positive correlation with the content of organic matter (r=0.904, P=0.013).