Gypsum Cave Biofilm Communities are Strongly Influenced by Bat- And Arthropod-Related Fungi.

The Gypsum Karst of Sorbas, Almeria, southeast Spain, includes a few caves whose entrances are open and allow the entry and roosting of numerous bats. Caves are characterized by their diversity of gypsum speleothems, such as stalactites, coralloids, gypsum crusts, etc. Colored biofilms can be observed on the walls of most caves, among which the Covadura and C3 caves were studied. The objective was to determine the influence that bat mycobiomes may have on the fungal communities of biofilms. The results indicate that the fungi retrieved from white and yellow biofilms in Covadura Cave (Ascomycota, Mortierellomycota, Basidiomycota) showed a wide diversity, depending on their location, and were highly influenced by the bat population, the guano and the arthropods that thrive in the guano, while C3 Cave was more strongly influenced by soil- and arthropod-related fungi (Ascomycota, Mortierellomycota), due to the absence of roosting bats.

Bacterial communities forming yellow biofilms in different cave types share a common core.

The walls of different types of caves under diverse geological settings (limestone, gypsum and volcanic) are colonized by biofilms of different colors: white, yellow, pink, grey, green to dark brown, but only a few colored biofilms such as the white, yellow and grey ones have been extensively studied. However, an assessment among the microbial communities originating these biofilms in different lithologies is lacking. Here we compare the yellow biofilms from two caves, Covadura and C3, in the Gypsum Karst of Sorbas in Spain, with those from two Spanish limestone caves (Pindal and Santian), and four volcanic caves in Spain and Italy (Viento, Honda del Bejenado, Grotta del Santo, Grotta di Monte Corruccio). The structure of yellow biofilms in gypsum caves closely resembles that found in other Spanish and European limestone caves. However, volcanic cave biofilms exhibit greater variability in their microbial community structure and morphologies. Biofilms from gypsum, limestone and volcanic caves were characterized by the abundance of the genera Crossiella and the gammaproteobacterial wb1-P19. The uncultured Euzebyaceae were abundant in gypsum and Spanish volcanic caves, while in the limestone and Italian volcanic caves, they were rare or absent. Nitrospira was also abundant in limestone and volcanic caves, but not in gypsum caves. Due to the abundances of Crossiella, gammaproteobacterial wb1-P19, and uncultured Euzebyaceae, in many different ecosystems, not only in caves, as recently reported, understanding the functional diversity in which these lineages are involved seems critical. Although we have studied a limited number of yellow biofilms from caves in Spain and Italy, data from other caves in USA and Russia also point out the existence of a similarity among the most abundant members composing the structure of yellow biofilms, suggesting that they share a common core.

Author Correction: The potential of gypsum speleothems for paleoclimatology: application to the Iberian Roman Humid Period.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The potential of gypsum speleothems for paleoclimatology: application to the Iberian Roman Human Period.

Carbonate cave deposits (speleothems) have been used widely for paleoclimate reconstructions; however, few studies have examined the utility of other speleothem-forming minerals for this purpose. Here we demonstrate for the first time that stable isotopes (δ17O, δ18O and δD) of structurally-bound gypsum (CaSO4·2H2O) hydration water (GHW) can be used to infer paleoclimate. Specifically, we used a 63 cm-long gypsum stalactite from Sima Blanca Cave to reconstruct the climate history of SE Spain from ~ 800 BCE to ~ 800 CE. The gypsum stalactite indicates wet conditions in the cave and humid climate from ~ 200 BCE to 100 CE, at the time of the Roman Empire apogee in Hispania. From ~ 100 CE to ~ 600 CE, evaporation in the cave increased in response to regional aridification that peaked at ~ 500-600 CE, roughly coinciding with the transition between the Iberian Roman Humid Period and the Migration Period. Our record agrees with most Mediterranean and Iberian paleoclimate archives, demonstrating that stable isotopes of GHW in subaerial gypsum speleothems are a useful tool for paleoclimate reconstructions.