SummaryIn order to investigate the food chain and energy balance of the chemolithoautotrophically-based ecosystem of the sulphur spring in Movile Cave as a model system for extraterrestrial life, a first sampling campaign was done. Microbial diversity and activity were analysed by MPN-enumeration methods and microcalorimetry, respectively. In addition, a speciation of the inorganic sulphur compounds by HPLC and IC techniques was performed. Metabolic activities were predominantly connected with thick microbial mats floating on the water surface of the cave. These mats showed an aerobic heat evolution of about 1200 µW/g and contained about 500 µmol/g elemental sulphur. In contrast, other samples collected from cave water, sediment and rock exhibited only activities of maximal 40 to 60 µW/g and contained only up to 2.5 µmol/g elemental sulphur. As the main primary producers aerobic and facultatively anaerobic sulphur oxidisers were identified at high numbers, occasionally exceeding 10 7 CFU/g. Methylotrophic bacteria were present in all samples at up to 10 6 CFU/g, indicating the important role of C1 metabolism for the cave ecosystem. Although reduced sulphur species were biologically oxidised to sulphuric acid, the pH values of the samples ranged from 6.5 to 8.2 due to the high buffering capacity of the cave walls, which consisted mainly of limestone. Surprisingly, not only neutrophilic but also extremely acidophilic bacteria were detected. Sulphate reducers were present in both aerobic and anaerobic zones. The data presented suggest a close interdependence of sulphur oxidation and reduction as well as carbon dioxide and other C1 compound metabolism in the most biologically active zone of the cave ecosystem, i.e. the floating microbial mats.
Abstract:Sulfur Cave (Puturosu Mountain, Romania) is an extreme environment, unique for displaying life in a gas chemocline. The lower part of the cave is filled with CO 2 , CH 4 , and H 2 S of mofettic origin, while the upper part contains air that floats above the heavier volcanic gasses. S° and H 2 SO 4 (from sulfur-oxidation) cover the cave wall at and below the CO 2 -H 2 S:O 2 gas/gas interface. On the cave wall, near the interface the pH is <1 and unusual microbial biofilms occur on the rock's surface. We provide context information on the geology, mineralogy, chemistry and biology to better understand this unique environment. We have used X-ray diffraction, optical microscopy, scanning electron microscopy with EDAX capabilities, stable isotope analysis and 16S and 18S rDNA amplicon sequencing. The most common taxa in the microbial biofilms are Mycobacteria, Acidithiobacillus and Ferroplasmaceae. Liquid water in this system originates solely from condensation of water vapor onto the cave walls making inflow of organic carbon from outside unlikely. The most likely primary source of energy for this microbial community is sulfur oxidation with H 2 S and S° as main reductants and atmospheric O 2 as the main oxidant. Ferric iron from the rock surface is another potential oxidant. In Sulfur Cave, gaseous CO 2 (from mofettic emission) maintains the stability of the gas chemocline. Sulfur Cave biofilms can help the search for extreme life in the subsurface, near volcanic systems on Earth and Mars. The Sulfur Cave example shows that a habitable environment can be established underground in gas chemoclines near CO 2 -dominated gas discharge zones, where it can have a steady supply of water and energy.
cu: Povezava med jamskimi minerali in termalnimi vodami bogatimi z žveplovodikom v dolini Cerne (JZ Romunija) V dolini Cerne, na jugoza�odu Romunije, je bilo v jurski� in kredni� apnenci� oblikovano več kot 100 jam. Za jame v tej regiji so izstopajoče tri značilnosti: prisotnost veliki� količin izločene sadre, veliko guana in visoka jamska temperatura. Visoko temperaturne anomalije niso značilne za običajno jamsko okolje. V določeni� jama�, v nižji� deli� doline Cerne, ponekod temperatura doseže 40ºC. Ta situacija je posledica prisotnosti termalni� vod, ki tečejo skozi jamo ali se nabirajo v bazeni� ter vroči� par, ki se dvigajo iz globin skozi razpoke. Posledica našteti� posebnosti so izjemni pogoji v jamskem okolju, ki dovoljujejo izločanje niza redki� mineralov. Ta študija predstavlja rezultate preiskav 57 vzorcev z rentgensko difrakcijo, geokemijo, Fourierjevo-transformacijsko infrardečo spektroskopijo in elektronsko mikroskopijo z namenom, da povežemo prisotnost jamski� mineralov z verjetnimi �ipogenimi speleogenetskimi procesi. Tukaj dokumentiramo prisotnost dvaindvajseti� sekundarni� jamski� mineralov, med katerimi je prisotnost apjonita in tamarugita prvič zabeležena v okolju jame razvite v apnenci�. Minerali pripadajo trem različnim združbam: s prevladujočimi sulfati (Diana Cave), s prevladujočimi fosfati (Adam S�aft), in sulfatno-fosfatno-nitratno bogata združba (Great Sălitrari Cave). Dodatna merjenja izotopov (δ34S) izvedena na sulfatni� kapniki�, so prispevala dodatne informacije o izvoru mineralov in jam. Ključne besede: jamski minerali, termalne vode, stabilni izotopi, �ipogena speleogeneza, dolina Cerne, Romunija.
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