Comparative analysis of yellow microbial communities growing on the walls of geographically distinct caves indicates a common core of microorganisms involved in their formation

Morphologically similar microbial communities that often form on the walls of geographically distinct limestone caves have not yet been comparatively studied. Here, we analysed phylotype distribution in yellow microbial community samples obtained from the walls of distinct caves located in S pain, C zech R epublic and S lovenia. To infer the level of similarity in microbial community membership, we analysed inserts of 474 16 S r RNA gene clones and compared those using statistical tools. The results show that the microbial communities under investigation are composed solely of B acteria . The obtained phylotypes formed three distinct groups of operational taxonomic units ( OTU s). About 60% of obtained sequences formed three core OTU s common to all three sampling sites. These were affiliated with actinobacterial P seudonocardinae (30–50% of sequences in individual sampling site libraries), but also with gammaproteobacterial C hromatiales (6–25%) and X anthomonadales (0.5–2.0%). Another 7% of sequences were common to two sampling sites and formed eight OTU s, while the remaining 35% were site specific and corresponded mostly to OTU s containing single sequences. The same pattern was observed when these data were compared with sequence data available from similar studies. This comparison showed that distinct limestone caves support microbial communities composed mostly of phylotypes common to all sampling sites.