Bat urea-derived minerals in arid environment. First identification of allantoin, C4H6N4O3, in Kahf Kharrat Najem Cave, United Arab Emirates

Kahf Kharrat Najem Cave is a small cave in United Arab Emirates (UAE) that hosts a bat colony which is the source of guano deposits and peculiar centimeter-long yellowish stalactites. The mineralogy and geochemistry of these deposits were analyzed using powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopic microanalysis (EDX), scanning electron microscope (SEM), and stable isotope composition (δ13C and δ15N). Urea CO(NH2)2 was found to be the main compound of these stalactites, while allantoin C4H6N4O3 was found to be an accessory urea byproduct. This paper is the first to mention allantoin in a cave environment. We also identified rare sulfate minerals (aphthitalite, alunite) and phosphates that probably correspond to the archerite-biphosphammite series. The occurrence of these rare bat-related minerals is due to the extremely dry conditions in the cave, which accounts for the extraordinary preservation of the guano deposits and allows for the crystallization of these very soluble minerals.Publisher PDFPeer reviewe

Bat urea-derived minerals in arid environment. First identification of allantoin, C\u3csub\u3e4\u3c/sub\u3eH\u3csub\u3e6\u3c/sub\u3eN\u3csub\u3e4\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e, in Kahf Kharrat Najem Cave, United Arab Emirates

Kahf Kharrat Najem Cave is a small cave in United Arab Emirates (UAE) that hosts a bat colony which is the source of guano deposits and peculiar centimeter-long yellowish stalactites. The mineralogy and geochemistry of these deposits were analyzed using powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopic microanalysis (EDX), scanning electron microscope (SEM), and stable isotope composition (δ13C and δ15N). Urea CO(NH2)2 was found to be the main compound of these stalactites, while allantoin C4H6N4O3 was found to be an accessory urea byproduct. This paper is the first to mention allantoin in a cave environment. We also identified rare sulfate minerals (aphthitalite, alunite) and phosphates that probably correspond to the archerite-biphosphammite series. The occurrence of these rare bat-related minerals is due to the extremely dry conditions in the cave, which accounts for the extraordinary preservation of the guano deposits and allows for the crystallization of these very soluble minerals

An Unusual Inverted Saline Microbial Mat Community in an Interdune Sabkha in the Rub' al Khali (the Empty Quarter), United Arab Emirates.

Salt flats (sabkha) are a recognized habitat for microbial life in desert environments and as analogs of habitats for possible life on Mars. Here we report on the physical setting and microbiology of interdune sabkhas among the large dunes in the Rub' al Khali (the Empty Quarter) in Liwa Oasis, United Arab Emirates. The salt flats, composed of gypsum and halite, are moistened by relatively fresh ground water. The result is a salinity gradient that is inverted compared to most salt flat communities with the hypersaline layer at the top and freshwater layers below. We describe and characterize a rich photosynthetically-based microbial ecosystem that is protected from the arid outside environment by a translucent salt crust. Gases collected from sediments under shallow ponds in the sabkha contain methane in concentrations as high as 3400 ppm. The salt crust could preserve biomarkers and other evidence for life in the salt after it dries out. Chloride-filled depressions have been identified on Mars and although surface flow of water is unlikely on Mars today, ground water is possible. Such a near surface system with modern groundwater flowing under ancient salt deposits could be present on Mars and could be accessed by surface rovers

Abundance and distribution of <i>Salinibacter</i> OTUs.

<p>Abundance and distribution of <i>Salinibacter</i> OTUs.</p

Select identities of closest cultured matches based on longest sequences for the phyla identified in each layer, using the NCBI BLASTN program.

<p>Proteobacteria representatives are additionally identified as belonging to the class <i>Alphaproteobacteria</i> (A), <i>Deltaproteobacteria</i> (D), or <i>Gammaproteobacteria</i> (G). The sequence similarity is indicated by ID% with similarities of 99% marked with bold type.</p

Schematic of the aquifer contained within the dunes of the Liwa Oasis.

<p>The base of the dunes is a relatively impermeable layer of carbonate close to sea level (striped layer). The solid line represents the dune profile, the dotted line the aquifer. Flow lines are shown as solid arrows and evaporation is indicated as wavy arrows. Discharge occurs at the lower elevations of the dune where the water table comes close to or intersects the surface. Evaporation occurs leaving behind salt. In the flat interdune spaces salt flats (sabkha) are formed. Figure adapted from Fig 2 of Wood and Imes [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0150342#pone.0150342.ref051" target="_blank">51</a>].</p

Salinity and pH of water samples, and gas composition of released bubbles from the sabkha subsurface.

<p>Salinity and pH of water samples, and gas composition of released bubbles from the sabkha subsurface.</p

Close up of an endoevaporite mat.

<p>The uppermost white layer, about 5 mm thick, is the salt crust. Below that is a layer, almost 5 mm thick of pink halophilic bacteria and below that a layer of green photosynthetic organisms. Below the green layer the material is darker in color. Gas samples were acquired from sediments beneath this mat. The mat pictured above was sectioned from top to bottom as follows–top layer (T) composed of white and pink layer; middle layer (M) composed of green layer; bottom layer (B) composed of darker brown layer; sediment layer (S) mostly composed of fine sand attached to the bottom of the dark brown layer.</p