RESUMEN
Cyanobacteria are adaptable and dominant organisms that exist in many harsh and extreme environments due to their great ecological tolerance. They produce various secondary metabolites, including cyanotoxins. While cyanobacteria are well studied in surface waters and some aerial habitats, numerous other habitats and niches remain underexplored. We collected 61 samples of: (i) biofilms from springs, (ii) aerial microbial mats from buildings and subaerial mats from caves, and (iii) water from borehole wells, caves, alkaline, saline, sulphidic, thermal, and iron springs, rivers, seas, and melted cave ice from five countries (Croatia, Georgia, Italy, Serbia, and Slovenia). We used (q)PCR to detect cyanobacteria (phycocyanin intergenic spacer-PC-IGS and cyanobacteria-specific 16S rRNA gene) and cyanotoxin genes (microcystins-mcyE, saxitoxins-sxtA, cylindrospermopsins-cyrJ), as well as amplicon sequencing and morphological observations for taxonomic identification. Cyanobacteria were detected in samples from caves, a saline spring, and an alkaline spring. While mcyE or sxtA genes were not observed in any sample, cyrJ results showed the presence of a potential cylindrospermopsin producer in a biofilm from a sulphidic spring in Slovenia. This study contributes to our understanding of cyanobacteria occurrence in diverse habitats, including rare and extreme ones, and provides relevant methodological considerations for future research in such environments.
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Cianobacterias , Ecosistema , Cianobacterias/genética , Cianobacterias/aislamiento & purificación , Toxinas Bacterianas/genética , ARN Ribosómico 16S/genética , Eslovenia , Biopelículas , Cuevas/microbiología , Toxinas de Cianobacterias , Microbiología del Agua , Monitoreo del Ambiente , Italia , Microcistinas/análisis , Microcistinas/genética , Serbia , CroaciaRESUMEN
The Winter Wonderland ice cave, located at an elevation of 3140 m above sea level in the Uinta Mountains of northern Utah, USA, maintains a constant sub-zero temperature. Seasonal snowmelt and rain enter the cave, freeze on the surface of the existing ice, and contribute to a 3-m-thick layered ice mass. This ice mass contains organic matter and cryogenic cave carbonates (CCCs) that date back centuries. In this study, samples of ice, liquid water, and exposed CCCs were collected to examine the bacterial communities within the cave and to determine if these communities vary spatially and between sample types. Flow cytometry showed that cell counts are an order of magnitude higher in liquid water samples than in ice. Epifluorescence microscopy and scanning electron microscopy imaging revealed potential coccoid and bacillus microbial morphologies in water samples and putative cells or calcite spherules in the CCCs. The diversity of bacteria associated with soil, identified through sequence-based analysis, supports the hypothesis that water enters the cave by filtering through soil and bedrock. A differential abundance of bacterial taxa was observed between sample types, with the greatest diversity found in CCCs. This supports a geomicrobiological framework where microbes aggregate in the water, sink into a concentrated layer, and precipitate out of the ice with the CCCs, thereby reducing the cell counts in the ice. These CCCs may provide essential nutrients for the bacteria or could themselves be products of biomineralization.
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Bacterias , Cuevas , Hielo , Utah , Bacterias/clasificación , Bacterias/genética , Bacterias/aislamiento & purificación , Cuevas/microbiología , Microbiología del Suelo , Biodiversidad , Microscopía Electrónica de Rastreo , Estaciones del Año , Microbiología del AguaRESUMEN
Quartzite caves located on table-top mountains (tepuis) in the Guyana Shield, are ancient, remote, and pristine subterranean environments where microbes have evolved peculiar metabolic strategies to thrive in silica-rich, slightly acidic and oligotrophic conditions. In this study, we explored the culturable fraction of the microbiota inhabiting the (ortho)quartzite cave systems in Venezuelan tepui (remote table-top mountains) and we investigated their metabolic and enzymatic activities in relation with silica solubilization and extracellular hydrolytic activities as well as the capacity to produce antimicrobial compounds. Eighty microbial strains were isolated with a range of different enzymatic capabilities. More than half of the isolated strains performed at least three enzymatic activities and four bacterial strains displayed antimicrobial activities. The antimicrobial producers Paraburkholderia bryophila CMB_CA002 and Sphingomonas sp. MEM_CA187, were further analyzed by conducting chemotaxonomy, phylogenomics, and phenomics. While the isolate MEM_CA187 represents a novel species of the genus Sphingomonas, for which the name Sphingomonas imawarii sp. nov. is proposed, P. bryophila CMB_CA002 is affiliated with a few strains of the same species that are antimicrobial producers. Chemical analyses demonstrated that CMB_CA002 produces ditropolonyl sulfide that has a broad range of activity and a possibly novel siderophore. Although the antimicrobial compounds produced by MEM_CA187 could not be identified through HPLC-MS analysis due to the absence of reference compounds, it represents the first soil-associated Sphingomonas strain with the capacity to produce antimicrobials. This work provides first insights into the metabolic potential present in quartzite cave systems pointing out that these environments are a novel and still understudied source of microbial strains with biotechnological potential.
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Bacterias , Cuevas , Filogenia , ARN Ribosómico 16S , Cuevas/microbiología , ARN Ribosómico 16S/genética , Bacterias/clasificación , Bacterias/metabolismo , Bacterias/aislamiento & purificación , Bacterias/genética , Dióxido de Silicio/química , Microbiota , Venezuela , Sphingomonas/metabolismo , Sphingomonas/aislamiento & purificación , Sphingomonas/clasificación , Sphingomonas/genética , Biotecnología/métodos , Antiinfecciosos/metabolismo , Antiinfecciosos/farmacología , Microbiología del Suelo , ADN Bacteriano/genéticaRESUMEN
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.
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Artrópodos , Biopelículas , Sulfato de Calcio , Cuevas , Quirópteros , Hongos , Cuevas/microbiología , Quirópteros/microbiología , Quirópteros/fisiología , Animales , Hongos/clasificación , Hongos/fisiología , Hongos/genética , Hongos/aislamiento & purificación , Artrópodos/microbiología , España , Biodiversidad , Micobioma , Microbiología del SueloRESUMEN
Lehman Caves is an extensively decorated high desert cave that represents one of the main tourist attractions in Great Basin National Park, Nevada. Although traditionally considered a water table cave, recent studies identified abundant speleogenetic features consistent with a hypogenic and, potentially, sulfuric acid origin. Here, we characterized white mineral deposits in the Gypsum Annex (GA) passage to determine whether these secondary deposits represent biogenic minerals formed during sulfuric acid corrosion and explored microbial communities associated with these and other mineral deposits throughout the cave. Powder X-ray diffraction (pXRD), scanning electron microscopy with electron dispersive spectroscopy (SEM-EDS), and electron microprobe analyses (EPMA) showed that, while most white mineral deposits from the GA contain gypsum, they also contain abundant calcite, silica, and other phases. Gypsum and carbonate-associated sulfate isotopic values of these deposits are variable, with δ34SV-CDT between +9.7 and +26.1, and do not reflect depleted values typically associated with replacement gypsum formed during sulfuric acid speleogenesis. Petrographic observations show that the sulfates likely co-precipitated with carbonate and SiO2 phases. Taken together, these data suggest that the deposits resulted from later-stage meteoric events and not during an initial episode of sulfuric acid speleogenesis. Most sedimentary and mineral deposits in Lehman Caves have very low microbial biomass, with the exception of select areas along the main tour route that have been impacted by tourist traffic. High-throughput 16S rRNA gene amplicon sequencing showed that microbial communities in GA sediments are distinct from those in other parts of the cave. The microbial communities that inhabit these oligotrophic secondary mineral deposits include OTUs related to known ammonia-oxidizing Nitrosococcales and Thaumarchaeota, as well as common soil taxa such as Acidobacteriota and Proteobacteria. This study reveals microbial and mineralogical diversity in a previously understudied cave and expands our understanding of the geomicrobiology of desert hypogene cave systems.
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Bacterias , Cuevas , Minerales , Cuevas/microbiología , Minerales/análisis , Bacterias/clasificación , Bacterias/metabolismo , Nevada , Archaea/metabolismo , Sedimentos Geológicos/microbiología , Sedimentos Geológicos/química , Parques Recreativos , ARN Ribosómico 16S/genética , Ácidos Sulfúricos , Filogenia , Microbiota , Sulfato de Calcio/química , Microscopía Electrónica de RastreoRESUMEN
Tidally-influenced subterranean settings represent natural geomicrobiological laboratories, relatively unexplored, that facilitate the investigation of new biomineralization processes. The unusual water chemistry of Zinzulùsa Cave and its oligotrophic and aphotic conditions have allowed the development of a unique ecosystem in which complex bacterial activities induce rare biomineralization processes. A diversified microbial community develops on centimeter-thick crusts that form in the submerged part of the cave. The crusts are formed of Ca-phosphate minerals, mostly carbonate-fluoroapatite (francolite), covered by a black crust, few microns in thickness, composed of ferromanganiferous oxides (hematite and vernadite). Diffuse coccoidal and filamentous bacteria and amorphous organic matter are mixed with the minerals. The micromorphologies and comparative 16S rRNA gene-based metabarcoding analyses identify a "core microbiota" also common to other natural environments characterized by FeMn and Ca-phosphate mineralization. The microbiota is characterized by nitrifying, sulfide/sulfur/thiosulfate-oxidizing and sulfate/thiosulfate/sulfur-reducing bacteria. In addition, manganese-oxidizing bacteria include the recently described "Ca. Manganitrophus noduliformans" and an abundance of bacteria belonging to the Planctomycetes-Verrucomicrobia-Chlamydiae (PVC) superphylum, as well as Haliangiales (fruiting body-forming bacteria) and Hyphomicrobiales (stalked and budding bacteria) that are known to produce extracellular polymers that trap iron and manganese oxides. 16S rRNA gene metabarcoding analysis showed the presence of bacteria able to utilize many organic P substrates, including Ramlibacter, and SEM images revealed traces of fossilized microorganisms resembling "cable bacteria", which may play a role in Ca-phosphate biomineralization. Overall, the data indicate biomineralization processes induced by microbial metabolic activities for both ferromanganiferous oxide and francolite components of these crusts.
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Biomineralización , Cuevas , Consorcios Microbianos , Italia , Cuevas/microbiología , Bacterias/metabolismo , Bacterias/clasificación , ARN Ribosómico 16S , MicrobiotaRESUMEN
BACKGROUND: Karst caves serve as natural laboratories, providing organisms with extreme and constant conditions that promote isolation, resulting in a genetic relationship and living environment that is significantly different from those outside the cave. However, research on cave creatures, especially Opiliones, remains scarce, with most studies focused on water, soil, and cave sediments. RESULTS: The structure of symbiotic bacteria in different caves were compared, revealing significant differences. Based on the alpha and beta diversity, symbiotic bacteria abundance and diversity in the cave were similar, but the structure of symbiotic bacteria differed inside and outside the cave. Microorganisms in the cave play an important role in material cycling and energy flow, particularly in the nitrogen cycle. Although microbial diversity varies inside and outside the cave, Opiliones in Beijing caves and Hainan Island exhibited a strong similarity, indicating that the two environments share commonalities. CONCLUSIONS: The karst cave environment possesses high microbial diversity and there are noticeable differences among different caves. Different habitats lead to significant differences in the symbiotic bacteria in Opiliones inside and outside the cave, and cave microorganisms have made efforts to adapt to extreme environments. The similarity in symbiotic bacteria community structure suggests a potential similarity in host environments, providing an explanation for the appearance of Sinonychia martensi in caves in the north.
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Bacterias , Cuevas , Ecosistema , Simbiosis , Cuevas/microbiología , Bacterias/genética , Bacterias/aislamiento & purificación , Bacterias/clasificación , China , Microbiota/fisiología , BiodiversidadRESUMEN
Cueva del Viento, located in the Canary Islands, Spain, is the Earth's sixth-longest lava tube, spanning 18,500 m, and was formed approximately 27,000 years ago. This complex volcanic cave system is characterized by a unique geomorphology, featuring an intricate network of galleries. Despite its geological significance, the geomicrobiology of Cueva del Viento remains largely unexplored. This study employed a combination of culture-dependent techniques and metabarcoding data analysis to gain a comprehensive understanding of the cave's microbial diversity. The 16S rRNA gene metabarcoding approach revealed that the coloured microbial mats (yellow, red and white) coating the cave walls are dominated by the phyla Actinomycetota, Pseudomonadota and Acidobacteriota. Of particular interest is the high relative abundance of the genus Crossiella, which is involved in urease-mediated biomineralization processes, along with the presence of genera associated with nitrogen cycling, such as Nitrospira. Culture-dependent techniques provided insights into the morphological characteristics of the isolated species and their potential metabolic activities, particularly for the strains Streptomyces spp., Paenarthrobacter sp. and Pseudomonas spp. Our findings underscore the potential of Cueva del Viento as an ideal environment for studying microbial diversity and for the isolation and characterization of novel bacterial species of biotechnological interest.
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Cuevas , Filogenia , ARN Ribosómico 16S , España , Cuevas/microbiología , ARN Ribosómico 16S/genética , Bacterias/clasificación , Bacterias/genética , Bacterias/aislamiento & purificación , ADN Bacteriano/genética , BiodiversidadRESUMEN
Castañar is a cave with strict visitor control measures since it was open to public visits in 2003. However, in recent years, the cave suffered two fungal outbreaks, the first in 2008 and controlled by cleaning the contaminated sediments and subsequent closure of the cave until 2014. The cave was reopened but limited to a maximum of 450 visitors/year. Despite these restrictions on visit, the cave experienced a second outbreak in 2021, originating from the installation of a steel grating walkway, aiming at protecting the ground sediments from the visitors' footsteps. Here, we conducted an analysis using Next-Generation Sequencing and culture-dependent techniques to investigate the fungal communities related to the second outbreak and compare with those present before the cave suffered the outbreak. The results show that the most abundant fungi involved in the 2021 outbreak were already detected in 2020, and even in 2008 and 2009, although the main species that originating both outbreaks were different, likely due to the different carbon sources introduced into the cave.
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Ecosistema , Hongos , Hongos/genética , España/epidemiología , Cuevas/microbiología , Brotes de EnfermedadesRESUMEN
Caves are unique environments characterized by spatial limitations, partial or total absence of direct light, and scarcity of organic carbon and nutrients. Caves are shelters for a variety of adapted animals and microorganisms such as fungi, many of which are still unknown. Amphichorda is a fungal genus belonging to the family Bionectriaceae, which includes cave-dwelling and entomopathogenic species with biotechnological applications. In this study, a new fungal species was identified using morphological and multi-locus phylogenetic analyses of the ITS, LSU, and TEF loci, in the Gruta Velha Nova limestone cave located in the Southern Espinhaço Range, Monjolos, Minas Gerais, Brazil. During the exposure of potato dextrose agar plates to the cave environment, an insect from the family Rhaphidophoridae passed by and fed on the culture medium, resulting in three fungal isolates. Phylogenetic analyses showed that these isolates formed a clade distinct from all known species, leading us to introduce a new species, Amphichorda monjolensis, which may be associated with this insect. Here, we also proposed two new combinations for species of acremonium-like fungi in the Bionectriaceae: Bulbithecium globosisporum (synonym: Acremonium globosisporum) and Hapsidospora curva (synonym: Acremonium curvum). The discovery of A. monjolensis highlights the potential of caves as shelters for new species with significant biotechnological importance.
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Cuevas , ADN de Hongos , Filogenia , Cuevas/microbiología , Brasil , ADN de Hongos/genética , Animales , Carbonato de Calcio , Acremonium/genética , Acremonium/clasificación , Acremonium/aislamiento & purificaciónRESUMEN
This study investigates the thermotolerant fungal biodiversity in caves and hot springs, focusing on their potential for extracellular enzyme production, specifically proteases. Samples were collected from the Cardonal region in Hidalgo, Mexico, using three different isolation methods. The study characterizes the morphological diversity of the isolated fungi and identifies various genera, including Aspergillus, Penicillium, Trichoderma, Cladosporium, and Fusarium, based on morphology. The isolated fungi were screened for their ability to produce extracellular enzymes on solid media, with a particular emphasis on proteases due to their industrial significance. Among the 35 isolated fungi, 20 exhibited proteolytic activity, and 12 strains were identified as good protease producers based on enzymatic index values. The study also evaluated the formation of fungal pellets by proteolytic fungi and found certain strains to display significant pellet formation. Additionally, protease production was examined by fungal pellets in submerged cultures, with isolate 6 demonstrating the highest protease activity. The findings highlight the diverse thermotolerant fungal biodiversity in extreme environments, and emphasize their potential for enzymatic production. This research contributes to our understanding of fungal ecology and provides insights into the biotechnological applications of these enzymes. The study recommends further molecular investigations to enhance biodiversity studies in such extreme environments.
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Hongos , Manantiales de Aguas Termales , Péptido Hidrolasas , Péptido Hidrolasas/biosíntesis , Péptido Hidrolasas/metabolismo , Hongos/enzimología , Hongos/aislamiento & purificación , Hongos/metabolismo , Manantiales de Aguas Termales/microbiología , Cuevas/microbiología , Biotecnología , Proteínas Fúngicas/metabolismo , Proteínas Fúngicas/biosíntesisRESUMEN
Cave heritage is often threatened by tourism or even scientific activities, which can lead to irreversible deterioration. We present a preventive conservation monitoring protocol to protect caves with rock art, focusing on La Garma Cave (Spain), a World Heritage Site with valuable archaeological materials and Palaeolithic paintings. This study assessed the suitability of the cave for tourist use through continuous microclimate and airborne particles monitoring, biofilm analysis, aerobiological monitoring and experimental visits. Our findings indicate several factors that make it inadvisable to adapt the cave for tourist use. Human presence and transit within the cave cause cumulative effects on the temperature of environmentally very stable and fragile sectors and significant resuspension of particles from the cave sediments. These environmental perturbations represent severe impacts as they affect the natural aerodynamic control of airborne particles and determine bacterial dispersal throughout the cave. This monitoring protocol provides part of the evidence to design strategies for sustainable cave management.
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Cuevas , Pinturas , Humanos , Cuevas/microbiología , España , Microclima , BacteriasRESUMEN
The physical and chemical characteristics of the bedrock, along with the geological and hydrological conditions of karst caves may influence the taxonomic and functional diversity of prokaryotes. Most studies so far have focused on microbial communities of caves including only a few samples and have ignored the chemical heterogeneity of different habitat types such as sampling sites, dripping water, carbonate precipitates, cave walls, cave sediment and surface soils connected to the caves. The aim of the present study was to compare the morphology, the composition and physiology of the microbiota in caves with similar environmental parameters (temperature, host rock, elemental and mineral composition of speleothems) but located in different epigenic karst systems. Csodabogyós Cave and Baradla Cave (Hungary) were selected for the analysis of bacterial and archaeal communities using electron microscopy, amplicon sequencing, X-ray diffraction, and mass spectroscopic techniques. The microbial communities belonged to the phyla Pseudomonadota, Acidobacteriota, Nitrospirota and Nitrososphaerota, and they showed site-specific variation in composition and diversity. The results indicate that morphological and physiological adaptations provide survival for microorganisms according to the environment. In epigenic karst caves, prokaryotes are prone to increase their adsorption surface, cooperate in biofilms, and implement chemolithoautotrophic growth with different electron-donors and acceptors available in the microhabitats.
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Cuevas , Microbiota , Cuevas/microbiología , Hungría , Bacterias/genética , Archaea/genética , Microbiota/genéticaRESUMEN
The Borra caves, the second largest subterranean karst cave ecosystem in the Indian sub-continent, are located at the Ananthagiri hills of Araku Valley in the Alluri district of Andhra Pradesh, India. The present investigation applied a shotgun metagenomic approach to gain insights into the microbial community structure, metabolic potential, and biosynthetic gene cluster (BGC) diversity of the microbes colonizing the surface of the speleothems from the aphotic zone of Borra caves. The taxonomic analysis of the metagenome data illustrated that the speleothem-colonizing core microbial community was dominated mainly by Alpha-, Beta-, and Gamma-Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes. The key energy metabolic pathways analysis provides strong evidence of chemolithoautotrophic and chemoheterotrophic modes of nutrition in the speleothem-colonizing microbial community. Metagenome data suggests that sulfur reducers and sulfur-disproportionating microbes might play a vital role in energy generation in this ecosystem. Our metagenome data also suggest that the dissimilatory nitrifiers and nitrifying denitrifiers might play an essential role in conserving nitrogen pools in the ecosystem. Furthermore, metagenome-wide BGCs mining retrieved 451 putative BGCs; NRPS was the most abundant (24%). Phylogenetic analysis of the C domain of NRPS showed that sequences were distributed across all six function categories of the known C domain, including several novel subclades. For example, a novel subclade had been recovered within the LCL domain clade as a sister subclade of immunosuppressant cyclosporin encoding C domain sequences. Our result suggested that subterranean cave microbiomes might be a potential reservoir of novel microbial metabolites.
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Bacterias , Metagenoma , Microbiota , Cuevas/microbiología , Microbiota/genética , Filogenia , Azufre , Bacterias/química , Bacterias/clasificación , Bacterias/aislamiento & purificaciónRESUMEN
Moonmilk is a cave deposit that was used for medical and cosmetic purposes and has lately raised interest for its antimicrobial potential. We studied five moonmilk samples from four caves with different microclimatic conditions, two temperate in north-western and northern Romania (Ferice, FaÈa Apei, and Izvorul TauÈoarelor caves) and one tropical in Minas Gerais, Brazil (Nestor Cave). The physicochemical and mineralogical analyses confirmed the presence of calcite and dolomite as the main phase in the moonmilk. A 16S rRNA gene-based metabarcoding approach showed the most abundant bacteria phyla Proteobacteria, GAL15, Actinobacteriota, and Acidobacteriota. The investigated caves differed in the dominant orders of bacteria, with the highest distance between the Romanian and Nestor Cave samples. Climate and, implicitly, the soil microbiome can be responsible for some differences we found between all the samples. However, other factors can be involved in shaping the moonmilk microbiome, as differences were found between samples in the same cave (Ferice). In our five moonmilk samples, 1 phylum, 70 orders (~ 36%), and 252 genera (~ 47%) were unclassified, which hints at the great potential of cave microorganisms for future uses.
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Cuevas , Microbiota , Cuevas/microbiología , ARN Ribosómico 16S/genética , Bacterias/genética , Proteobacteria/genéticaRESUMEN
In the absence of sunlight, caves harbor a great diversity of microbial colonies to extensive biofilms with different sizes and colors visible to the naked eye. One of the most widespread and visible types of biofilm are those with yellow hues that can constitute a serious problem for the conservation of cultural heritage in many caves, such as Pindal Cave (Asturias, Spain). This cave, declared a World Heritage Site by UNESCO for its Paleolithic parietal art, shows a high degree of development of yellow biofilms that represents a real threat to the conservation of painted and engraved figures. This study aims to: 1) identify the microbial structures and the most characteristic taxa composing the yellow biofilms, 2) seek the linked microbiome reservoir primarily contributing to their growth; 3) seed light on the driving vectors that contribute to their formation and determine the subsequent proliferation and spatial distribution. To achieve this goal, we used amplicon-based massive sequencing, in combination with other techniques such as microscopy, in situ hybridization and environmental monitoring, to compare the microbial communities of yellow biofilms with those of drip waters, cave sediments and exterior soil. The results revealed microbial structures related to the phylum Actinomycetota and the most characteristic bacteria in yellow biofilms, represented by the genera wb1-P19, Crossiella, Nitrospira, and Arenimonas. Our findings suggest that sediments serve as potential reservoirs and colonization sites for these bacteria that can develop into biofilms under favorable environmental and substrate conditions, with a particular affinity for speleothems and rugged-surfaced rocks found in condensation-prone areas. This study presents an exhaustive study of microbial communities of yellow biofilms in a cave, which could be used as a procedure for the identification of similar biofilms in other caves and to design effective conservation strategies in caves with valuable cultural heritage.
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Bacterias , Cuevas , Cuevas/microbiología , España , Ecología , BiopelículasRESUMEN
Karst caves are potential sinks of atmospheric methane due to microbial consumption. However, knowledge gaps on methanogens (methane producing microorganisms) and their interaction with methane-oxidizing bacteria (MOB) hinder our further understanding about methane dynamics in karst caves. Here we reported methanogenic community composition and their interaction with MOBs in the Heshang Cave to comprehensively understand methane cycling in subsurface biosphere. MOBs in karst cave were dominated by high-affinity MOB, upland soil cluster (USC), with USCγ pmoA gene abundance within the range of 1.34 × 104 to 1.8 × 107 copies·g-1 DW. In contrast, methanogens were dominated by Methanoregula and cluster ZC-I. The mcrA numbers were 7.21 × 103 to 8.31 × 104 copies·g-1 DW, 1-3 orders of magnitude lower than those of MOB. The inter-domain network analysis indicated that MOBs and methanogens cooperated more in the interior of the cave. Despite of the higher number of methanogenic nodes in the network, MOB dominated the keystone taxa, suggesting a leading functional role of MOB. MOB in caves showed a comparable with or higher potential methane oxidizing rate (PMOR, 0.63 ng CH4·g-1 DW·h-1 in sediment versus 11.02 ng CH4·g-1 DW·h-1 in weathered rock) than those in soils, whereas methane produced by methanogens was undetected. Collectively, high absolute abundances of MOB, high PMORs, the dominance of methanotrophic keystone taxa in the inter-domain network confirmed the superiority of MOBs over methanogens in the oligotrophic karst cave, mounting new evidence on caves as an important methane sink in terms of the interaction between methanogens and MOBs.
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Metano , Methylococcaceae , Cuevas/microbiología , Microbiología del Suelo , SueloRESUMEN
Fungi can colonize organic matter present in subterranean sites and have a significant role as dwellers in different microniches of cave habitats. In order to analyze the content of airborne fungal propagules in different parts of "Stopica Cave," a touristic site in Serbia, air sampling was carried out in three seasons during 2020, prior to and during the onset of COVID-19 pandemic. Culturable mycobiota was identified using both microscopic techniques and ITS region/BenA gene barcoding, while multivariate analyses were employed to establish the link between fungal taxa and different environmental factors. The maximal measured fungal propagule concentrations were recorded during spring sampling which were based on fungal propagule concentration categories; the cave environment matches the category V. A total of 29 fungal isolates were identified, while Aspergillus, Cladosporium, Fusarium, Lecanicillium, Mucor, and Penicillium were the most diverse genera. According to the trophic mode, most of the isolated fungal species were pathotrophs (75.86%), but when regarding ecological guilds, the most dominant were undefined saprobes and animal pathogens (41.38% for each). Show caves are especially vulnerable to human impacts, and the fungal propagules' concentration within the caves could be good indices for the level of ecological disturbance.
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COVID-19 , Hongos , Animales , Humanos , Cuevas/microbiología , Serbia , Pandemias , Estaciones del Año , Microbiología del Aire , Monitoreo del Ambiente/métodosRESUMEN
Anthropogenic disturbance on natural ecosystems is growing in frequency and magnitude affecting all ecosystems components. Understanding the response of different types of biocoenosis to human disturbance is urgently needed and it can be achieved by adopting a metacommunity framework. With the aid of advanced molecular techniques, we investigated sediment communities of Fungi, Bacteria and Archaea in four Italian show caves, aiming to disentangle the effects induced by tourism on their diversity and to highlight changes in the driving forces that shape their community composition. We modelled diversity measures against proxies of tourism pressure. With this approach we demonstrate that the cave tourism has a direct effect on the community of Bacteria and an indirect influence on Fungi and Archaea. By analysing the main driving forces influencing the community composition of the three microbial groups, we highlighted that stochastic factors override dispersal-related processes and environmental selection in show caves compared to undisturbed areas. Thanks to this approach, we provide new perspectives on the dynamics of microbial communities under human disturbance suggesting that a proper understanding of the underlying selective mechanisms requires a comprehensive and multi-taxonomic approach.
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Microbiota , Turismo , Humanos , Cuevas/microbiología , Bacterias , Archaea , HongosRESUMEN
While microbial communities in limestone caves across the world are relatively understood, knowledge of the microbial composition in lava tubes is lagging behind. These caves are found in volcanic regions worldwide and are typically lined with multicolored microbial mats on their walls and ceilings. The Mount Etna (Sicily, S-Italy) represents one of the most active volcanos in the world. Due to its outstanding biodiversity and geological features, it was declared Natural Heritage of Humanity by the UNESCO in 2013. Despite the presence of more than 200 basaltic lava tubes, the microbial diversity of these hypogean systems has never been investigated so far. Here, we investigated bacterial communities in four lava tubes of Mount Etna volcano. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features. We documented an abundant presence of microbial cells with different morphotypes including rod-shaped, filamentous, and coccoidal cells with surface appendages, resembling actinobacteria reported in other lava tubes across the world. Based on 16S rRNA gene analysis, the colored microbial mats collected were mostly composed of bacteria belonging to the phyla Actinomycetota, Pseudomonadota, Acidobacteriota, Chloroflexota, and Cyanobacteria. At the genus level, the analysis revealed a dominance of the genus Crossiella, which is actively involved in biomineralization processes, followed by Pseudomonas, Bacillus, Chujaibacter, and Sphingomonas. The presence of these taxa is associated with the carbon, nitrogen, and ammonia cycles, and some are possibly related to the anthropic disturbance of these caves. This study provides the first insight into the microbial diversity of the Etna volcano lava tubes, and expands on previous research on microbiology of volcanic caves across the world.