Bio- and geodiversity of vermiculations from Pertosa-Auletta Cave (southern Italy)

Caves are largely unknown environments, hosting in their peculiar ecological niches a wide diversity of extremophile microorganisms, highly specialized and adapted to the prohibitive conditions of caves (1). The role of cave biota in the formation of enigmatic structures occurring in underground environments, like vermiculations, is still largely unexplored (2). Vermiculations are thin, irregular and discontinuous deposits of incoherent particles, commonly found on the walls and ceilings of natural or artificial caves, worldwide (3). They show several kinds of morphology (dots, dendritic, hieroglyphic…), color (red, brown, grey, white) and size (4), and are considered “life hotspots”, representing a valuable focus for scientists and researchers in the field of cave microbiology. The aim of this study, funded by MIdA Foundation (Italy), was to investigate the microbiological and physico- chemical properties of vermiculations from Pertosa-Auletta Cave (Campania, southern Italy), in order to clarify the mechanisms involved in their formation and to define the factors affecting their diversification. Indeed, the understanding of biodiversity and genesis of vermiculations is a key step toward the protection and conservation of these peculiar biosignatures. Vermiculations from Pertosa-Auletta Cave, abundant in all the galleries, showed a considerable variety of morphologies. Overall, X-ray diffraction analysis indicated calcite and quartz as the dominant minerals of the 15 vermiculations studied, whereas clay minerals were almost absent. Elemental analysis showed wide variations in C, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, N, Na, Ni, P, S, Ti, V, and Zn concentrations among vermiculations. Applying the most innovative techniques in molecular biology, only Prokaryotes were observed. In particular, 16S rRNA gene-specific next generation sequencing analysis showed that Proteobacteria (48.0%) was the most abundant phylum in the Bacteria domain, followed by Acidobacteria (11.6%), Actinobacteria (7.1%), Nitrospirae (5.8%), Firmicutes (4.3%), Planctomycetes (3.2%), Chloroflexi (1.9%), and Gemmatimonadetes (1.1%). Archaea (0.1%) and a significant percentage of unclassified microorganisms (13.1%) were also observed. Clustering analysis suggested that microbial communities dwelling in the deposits partially influence their morphologies, likely mainly dependent on physico-chemical factors. Confocal laser scanning and field emission scanning electron microscopy confirmed the presence of active microbial mats, suggesting they may have an important role in the formation of vermiculations, throughout a number of processes, like production of organic matter, precipitation of secondary minerals (e.g. biogenic calcite), enhancement of sediment trapping and binding, etching or pitting of the host rock. 1) K. Tomczyk-Żak, U. Zielenkiewicz (2016) Geomicrobiology J., 33, 1-20 2) A. Bini, M. Cavalli Gori, S. Gori (1978) Int. J. Speleology, 10, 11-33 3) C.A. Hill, P. Forti (1997) Cave Minerals of the World. National Speleological Society, Ed. 2, 463 pp. 4) P. Parenzan (1961) Memoria Rassegna Speleologica Italiana, 5(2), 120-12