Diversity of microbial communities colonizing the walls of a Karstic cave in Slovenia.

Karstic cave systems in Slovenia receive substantial amounts of organic input from adjacent forest and freshwater systems. These caves host microbial communities that consist of distinct small colonies differing in colour and shape. Visible to the naked eye, the colonies cover cave walls and are strewn with light-reflecting water droplets. In this study, the diversity of prokaryotes constituting these unusual microbial communities in Pajsarjeva jama cave was examined. A molecular survey based on small subunit rRNA diversity showed a high diversity within the Bacteria, while members of Archaea were not recovered. A total of eight bacterial phyla were detected. The application of various species richness estimators confirmed the diverse nature of the microbial community sample. Members of Gammaproteobacteria were most abundant in the clone libraries constructed and were followed in abundance by members of Actinobacteria and Nitrospira. In addition, members of Alphaproteobacteria, Betaproteobacteria and Deltaproteobacteria as well as Acidobacteria, Verrucomicrobia, Planctomycetes, Chloroflexi and Gemmatimonadetes were identified in clone libraries. The high number of clones most closely related to environmental 16S rRNA gene clones showed the broad spectrum of unknown and yet to be cultivated microorganisms inhabiting these cave systems.