Geomicrobiology of a seawater-influenced active sulfuric acid cave.

Fetida Cave is an active sulfuric acid cave influenced by seawater, showing abundant microbial communities that organize themselves under three main different morphologies: water filaments, vermiculations and moonmilk deposits. These biofilms/deposits have different cave distribution, pH, macro- and microelement and mineralogical composition, carbon and nitrogen content. In particular, water filaments and vermiculations had circumneutral and slightly acidic pH, respectively, both had abundant organic carbon and high microbial diversity. They were rich in macro- and microelements, deriving from mineral dissolution, and, in the case of water filaments, from seawater composition. Vermiculations had different color, partly associated with their mineralogy, and unusual minerals probably due to trapping capacities. Moonmilk was composed of gypsum, poor in organic matter, had an extremely low pH (0\u20131) and low microbial diversity. Based on 16S rRNA gene analysis, the microbial composition of the biofilms/deposits included autotrophic taxa associated with sulfur and nitrogen cycles and biomineralization processes. In particular, water filaments communities were characterized by bacterial taxa involved in sulfur oxidation and reduction in aquatic, aphotic, microaerophilic/anoxic environments (Campylobacterales, Thiotrichales, Arenicellales, Desulfobacterales, Desulforomonadales) and in chemolithotrophy in marine habitats (Oceanospirillales, Chromatiales). Their biodiversity was linked to the morphology of the water filaments and their collection site. Microbial communities within vermiculations were partly related to their color and showed high abundance of unclassified Betaproteobacteria and sulfur-oxidizing Hydrogenophilales (including Sulfuriferula), and Acidiferrobacterales (including Sulfurifustis), sulfur-reducing Desulfurellales, and ammonia-oxidizing Planctomycetes and Nitrospirae. The microbial community associated with gypsum moonmilk showed the strong dominance (>60%) of the archaeal genus Thermoplasma and lower abundance of chemolithotrophic Acidithiobacillus, metal-oxidizing Metallibacterium, Sulfobacillus, and Acidibacillus. This study describes the geomicrobiology of water filaments, vermiculations and gypsum moonmilk from Fetida Cave, providing insights into the microbial taxa that characterize each morphology and contribute to biogeochemical cycles and speleogenesis of this peculiar seawater-influenced sulfuric acid cave

Morphology and evolution of sulphuric acid caves in South Italy

Sulphuric acid speleogenesis (SAS) related to the upwelling of acid water enriched in H2S and CO2 represents an unusual way of cave development. Since meteoric infiltration waters are not necessarily involved in speleogenesis, caves can form without the typical associated karst expressions (i.e. dolines) at the surface. The main mechanism of sulphuric acid dissolution is the oxidation of H2S (Jones et al., 2015) which can be amplified by bacterial mediation (Engel et al., 2004). In these conditions, carbonate dissolution associated with gypsum replacement, is generally believed to be faster than the normal epigenic one (De Waele et al., 2016). In Italy several SAS caves have been identified, but only few systems have been studied in detail: Frasassi and Acquasanta Terme (Marche)(Galdenzi et al., 2010), Monte Cucco (Umbria) (Galdenzi & Menichetti, 1995), and Montecchio (Tuscany) (Piccini et al., 2015). Other preliminary studies have been carried out in Calabria (Galdenzi, 2007) and Sicily (De Waele et al., 2016). Several less studied SAS cave systems located in South Italy, and in particular in Apulia (Santa Cesarea Terme), Sicily (Acqua Fitusa, Acqua Mintina) and Calabria (Mt. Sellaro and Cassano allo Ionio) have been selected in the framework of a PhD thesis on SAS caves and their speleogenesis. Using both limestone tablet weight loss (Galdenzi et al., 2012) and micro erosion meter (MEM) (Furlani et al., 2010) methods the dissolution rate above and under water in the caves will be quantified. Geomorphological observations, landscape analysis using GIS tools, and the analysis of gypsum and other secondary minerals (alunite and jarosite) (stable isotopes and dating) will help to reconstruct the speleogenetic stages of cave formation. Preliminary microbiological analysis will determine the microbial diversity and ecology in the biofilms

Secondary Minerals From Italian Sulfuric Acid Caves

Italy is a country hosting a large number of hypogenic sulfuric acid (SAS) speleogenesis caves, mostly located along the Apennine chain, but also in Campania (along the coastline of Capo Palinuro), Apulia (along the coastline of Santa Cesarea Terme) and Sicily. Besides the typical morphologies related to their special geochemical origin (cupolas, replacement pockets, bubble trails, etc), these caves often host abundant secondary mineral deposits, mainly gypsum, being the result of the interaction between the sulfuric acid and the carbonate host rock. Native sulfur deposits are also well visible on the ceiling and roof, and peculiar sulfuric acid minerals such as jarosite, alunite, and other sulfates like copiapite, pickeringite, tschermigite, tamarugite (probably related to the weathering of native clay minerals) have been found in those caves. The presence of typical SAS minerals, together with the morphologies, testifies the influence of rising acidic waters, that likely interact with the deep-seated Triassic evaporite deposits (along the Apennine chain), with volcanic sources or hydrothermal springs in the Tyrrhenian sea (in Campania) and with marine waters that infiltrate on the sea bottom and rise through deep faults (in Apulia). This paper describes the secondary minerals discovered in several caves, and discusses their origin and possible use in reconstructing the evolution of these cave systems

Vermiculations from karst caves: The case of Pertosa-Auletta system (Italy)

Unlike the spectacular speleothems that can often be found in numerous caves, vermiculations are rather unassuming formations, whose origin and evolution still subject of several heated debates. In order to provide a quantitative basis for the understanding of the nature and evolution of vermiculations in karst environments, the geochemical properties of one of the most important karst systems of southern Italy, the Pertosa-Auletta Cave, were studied through a comprehensive approach which included elemental, mineralogical and microscopy analyses. The chemical element abundances, mineral composition and microstructure of the vermiculations covering the entire range of morphologies and colours observed in the case-study cave were investigated, thus providing the first quantitative record of these traits. The vermiculations presented exceptional diversity in their morphology, colour, chemical and mineral composition, with it being due to exogenous determinants such as the deposition of stream sediments or organic matter as well as the development of photoautotrophic communities. They were invariably composed of calcite, associated to quartz as well as clays and other secondary minerals, the formation of which may be biologically mediated. This occurrence, and the evidences of microbial activity observed through dissolution traces, support the possible involvement of biogenic processes in vermiculation development

Flank Margin Caves In Telogenetic Limestones In Italy

Almost 20% of Italy is characterized by the outcropping of carbonate massifs ranging in age from Cambrian to Quaternary. Coastal karst is present in many Italian regions: from North-East to South and West: the Gulf of Trieste, the Conero (South of Ancona, Marche), the Adriatic coast of Apulia including Gargano, Murge and Salento, Maratea in Basilicata, Cilento in Campania, Circeo and Gaeta in Latium, Argentario and Giannutri Island in Tuscany, the southernmost part of the Ligurian Alps, Palermo Mts., San Vito Lo Capo, Syracuse coast and Marettimo Island in Sicily, and, especially, in Sardinia, which has carbonate rocks touching the sea along the coast of Balai near Porto Torres, Capo Caccia-Punta Giglio (Alghero), Sinis and Buggerru along the western litoral, Capo Teulada and Capo Sant\u2019Elia at Cagliari, Capo Figari, Tavolara Island and the Gulf of Orosei along the eastern mountainside. Recent researches have revealed several coastal cave systems that have a clear origin by mixing corrosion, in which the aggressive solution derives from the mixing between saline and fresh water at the watertable interface (the so-called flank margin caves). Glacioeustasy and tectonic movements can control the position of sea level with respect to coastal carbonate outcrops. For this reason these coastal caves represent useful records of sea-level stillstands. These caves are normally organized in sub-horizontal levels, and are characterized by the lack of high flow velocity markers (scallops) and alluvial sediments. Instead, they show rounded cave passage morphologies, often with horizontal wall notches, a characteristic swiss-cheese or sponge morphology, and passages that narrow going away from the coastline (due to the decreasing of sea water influence and mixing-corrosion effect). This paper describes some flank margin cave systems found in Apulia, Sicily, and Sardinia. In particular, five cave systems are illustrated: Sant\u2019Angelo caves (Apulia), Pellegrino and Rumena caves (Sicily), and Giuanniccu Mene cave and Fico cave (Sardinia), explaining their relationship with past sea levels and local uplift rate

Microbial mediation of complex subterranean mineral structures

Helictites\u2014an enigmatic type of mineral structure occurring in some caves\u2014differ from classical speleothems as they develop with orientations that defy gravity. While theories for helictite formation have been forwarded, their genesis remains equivocal. Here, we show that a remarkable suite of helictites occurring in Asperge Cave (France) are formed by biologically-mediated processes, rather than abiotic processes as had hitherto been proposed. Morphological and petro-physical properties are inconsistent with mineral precipitation under purely physico-chemical control. Instead, microanalysis and molecular-biological investigation reveals the presence of a prokaryotic biofilm intimately associated with the mineral structures. We propose that microbially-influenced mineralization proceeds within a gliding biofilm which serves as a nucleation site for CaCO3, and where chemotaxis influences the trajectory of mineral growth, determining the macroscopic morphology of the speleothems. The influence of biofilms may explain the occurrence of similar speleothems in other caves worldwide, and sheds light on novel biomineralization processes