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Santorini Island (Greece) is an active volcano which has alternated between dormant and active periods over the last 650,000 years with the latest volcanic unrest occurring in 2011–2012. Here we report a geochemical survey of fumarolic gases collected at Nea Kameni islet located in the center of the caldera over the period 2015–2022 in order to study the activity of the volcano and changes in hydrothermal conditions. This period is marked by the absence of significant geochemical anomalies compared to the unrest of 2011–2012, implying that no new magma upwelling has occurred. This is evident from the low CO2/CH4 ratio and H2 concentration of fumaroles. An increase of the atmospheric contribution in gases after the 2011–2012 unrest suggests a decrease of the deep gas flow and the chemical and C-He-isotope compositions are compatible with a model of Rayleigh fractionation in which CO2 dissolves in water at decreasing temperatures over time. These results are consistent with temperature estimates obtained using the H2/N2 geothermometer, seismic and geodetic evidences. This implies a slowing of the degassing of the hydrothermal/volcanic system and a cooling of the magma injected at shallow depth in 2011–2012. All these conclusions support a quiescent state of the Santorini volcano over the period 2015–2022.

Submarine hydrothermal systems along active volcanic ridges and arcs are highly dynamic, responding to both oceanographic (e.g., currents, tides) and deep-seated geological forcing (e.g., magma eruption, seismicity, hydrothermalism, and crustal deformation, etc.). In particular, volcanic and hydrothermal activity may also pose profoundly negative societal impacts (tsunamis, the release of climate-relevant gases and toxic metal(loid)s). These risks are particularly significant in shallow (<1000m) coastal environments, as demonstrated by the January 2022 submarine paroxysmal eruption by the Hunga Tonga-Hunga Ha’apai Volcano that destroyed part of the island, and the October 2011 submarine eruption of El Hierro (Canary Islands) that caused vigorous upwelling, floating lava bombs, and natural seawater acidification. Volcanic hazards may be posed by the Kolumbo submarine volcano, which is part of the subduction-related Hellenic Volcanic Arc at the intersection between the Eurasian and African tectonic plates. There, the Kolumbo submarine volcano, 7 km NE of Santorini and part of Santorini’s volcanic complex, hosts an active hydrothermal vent field (HVF) on its crater floor (~500m b.s.l.), which degasses boiling CO2–dominated fluids at high temperatures (~265°C) with a clear mantle signature. Kolumbo’s HVF hosts actively forming seafloor massive sulfide deposits with high contents of potentially toxic, volatile metal(loid)s (As, Sb, Pb, Ag, Hg, and Tl). The proximity to highly populated/tourist areas at Santorini poses significant risks. However, we have limited knowledge of the potential impacts of this type of magmatic and hydrothermal activity, including those from magmatic gases and seismicity. To better evaluate such risks the activity of the submarine system must be continuously monitored with multidisciplinary and high resolution instrumentation as part of an in-situ observatory supported by discrete sampling and measurements. This paper is a design study that d

Galdieria sulphuraria is a unicellular red alga that lives in hot, acidic, toxic metal-rich, volcanic environments, where few other organisms survive. Its genome harbors up to 5% of genes that were most likely acquired through horizontal gene transfer. These genes probably contributed to G.sulphuraria's adaptation to its extreme habitats, resulting in today's polyextremophilic traits. Here, we applied RNA-sequencing to obtain insights into the acclimation of a thermophilic organism towards temperatures below its growth optimum and to study how horizontally acquired genes contribute to cold acclimation. A decrease in growth temperature from 42C/46C to 28C resulted in an upregulation of ribosome biosynthesis, while excreted proteins, probably components of the cell wall, were downregulated. Photosynthesis was suppressed at cold temperatures, and transcript abundances indicated that C-metabolism switched from gluconeogenesis to glycogen degradation. Folate cycle and S-adenosylmethionine cycle (one-carbon metabolism) were transcriptionally upregulated, probably to drive the biosynthesis of betaine. All these cold-induced changes in gene expression were reversible upon return to optimal growth temperature. Numerous genes acquired by horizontal gene transfer displayed temperature-dependent expression changes, indicating that these genes contributed to adaptive evolution in G.sulphuraria.

Rapid fluctuation of environmental conditions can impose severe stress upon living organisms. Surviving such episodes of stress requires a rapid acclimation response, e.g., by transcriptional and post-transcriptional mechanisms. Persistent change of the environmental context, however, requires longer-term adaptation at the genetic level. Fast-growing unicellular aquatic eukaryotes enable analysis of adaptive responses at the genetic level in a laboratory setting. In this study, we applied continuous cold stress (28 degrees C) to the thermoacidophile red alga G. sulphuraria, which is 14 degrees C below its optimal growth temperature of 42 degrees C. Cold stress was applied for more than 100 generations to identify components that are critical for conferring thermal adaptation. After cold exposure for more than 100 generations, the cold-adapted samples grew similar to 30% faster than the starting population. Whole-genome sequencing revealed 757 variants located on 429 genes (6.1% of the transcriptome) encoding molecular functions involved in cell cycle regulation, gene regulation, signaling, morphogenesis, microtubule nucleation, and transmembrane transport. CpG islands located in the intergenic region accumulated a significant number of variants, which is likely a sign of epigenetic remodeling. We present 20 candidate genes and three putative cis-regulatory elements with various functions most affected by temperature. Our work shows that natural selection toward temperature tolerance is a complex systems biology problem that involves gradual reprogramming of an intricate gene network and deeply nested regulators.

The role and extent of horizontal gene transfer (HGT) in eukaryotes are hotly disputed topics that impact our understanding of the origin of metabolic processes and the role of organelles in cellular evolution. We addressed this issue by analyzing 10 novel Cyanidiales genomes and determined that 1% of their gene inventory is HGT-derived. Numerous HGT candidates share a close phylogenetic relationship with prokaryotes that live in similar habitats as the Cyanidiales and encode functions related to polyextremophily. HGT candidates differ from native genes in GC-content, number of splice sites, and gene expression. HGT candidates are more prone to loss, which may explain the absence of a eukaryotic pan-genome. Therefore, the lack of a pan-genome and cumulative effects fail to provide substantive arguments against our hypothesis of recurring HGT followed by differential loss in eukaryotes. The maintenance of 1% HGTs, even under selection for genome reduction, underlines the importance of non-endosymbiosis related foreign gene acquisition.

Galdieria sulphuraria is a unicellular red alga that lives in hot, acidic, toxic metal-rich, volcanic environments, where few other organisms survive. Its genome harbors up to 5% of genes that were most likely acquired through horizontal gene transfer. These genes probably contributed to G.sulphuraria's adaptation to its extreme habitats, resulting in today's polyextremophilic traits. Here, we applied RNA-sequencing to obtain insights into the acclimation of a thermophilic organism towards temperatures below its growth optimum and to study how horizontally acquired genes contribute to cold acclimation. A decrease in growth temperature from 42C/46C to 28C resulted in an upregulation of ribosome biosynthesis, while excreted proteins, probably components of the cell wall, were downregulated. Photosynthesis was suppressed at cold temperatures, and transcript abundances indicated that C-metabolism switched from gluconeogenesis to glycogen degradation. Folate cycle and S-adenosylmethionine cycle (one-carbon metabolism) were transcriptionally upregulated, probably to drive the biosynthesis of betaine. All these cold-induced changes in gene expression were reversible upon return to optimal growth temperature. Numerous genes acquired by horizontal gene transfer displayed temperature-dependent expression changes, indicating that these genes contributed to adaptive evolution in G.sulphuraria.

The role and extent of horizontal gene transfer (HGT) in eukaryotes are hotly disputed topics that impact our understanding of the origin of metabolic processes and the role of organelles in cellular evolution. We addressed this issue by analyzing 10 novel Cyanidiales genomes and determined that 1% of their gene inventory is HGT-derived. Numerous HGT candidates share a close phylogenetic relationship with prokaryotes that live in similar habitats as the Cyanidiales and encode functions related to polyextremophily. HGT candidates differ from native genes in GC-content, number of splice sites, and gene expression. HGT candidates are more prone to loss, which may explain the absence of a eukaryotic pan-genome. Therefore, the lack of a pan-genome and cumulative effects fail to provide substantive arguments against our hypothesis of recurring HGT followed by differential loss in eukaryotes. The maintenance of 1% HGTs, even under selection for genome reduction, underlines the importance of non-endosymbiosis related foreign gene acquisition.

Rapid fluctuation of environmental conditions can impose severe stress upon living organisms. Surviving such episodes of stress requires a rapid acclimation response, e.g., by transcriptional and post-transcriptional mechanisms. Persistent change of the environmental context, however, requires longer-term adaptation at the genetic level. Fast-growing unicellular aquatic eukaryotes enable analysis of adaptive responses at the genetic level in a laboratory setting. In this study, we applied continuous cold stress (28 degrees C) to the thermoacidophile red alga G. sulphuraria, which is 14 degrees C below its optimal growth temperature of 42 degrees C. Cold stress was applied for more than 100 generations to identify components that are critical for conferring thermal adaptation. After cold exposure for more than 100 generations, the cold-adapted samples grew similar to 30% faster than the starting population. Whole-genome sequencing revealed 757 variants located on 429 genes (6.1% of the transcriptome) encoding molecular functions involved in cell cycle regulation, gene regulation, signaling, morphogenesis, microtubule nucleation, and transmembrane transport. CpG islands located in the intergenic region accumulated a significant number of variants, which is likely a sign of epigenetic remodeling. We present 20 candidate genes and three putative cis-regulatory elements with various functions most affected by temperature. Our work shows that natural selection toward temperature tolerance is a complex systems biology problem that involves gradual reprogramming of an intricate gene network and deeply nested regulators.

In 2011-2012, Santorini was characterized by seismic-geodetic-geochemical unrest, which was unprecedented since the most-recent eruption occurred in 1950 and led to fear an eruption was imminent. This unrest offered a chance for investigating the processes leading to volcanic reactivation and the compositional characteristics of involved magma. We have thus analyzed the He-Ne-Ar-isotope composition of fluid inclusions in olivines and clinopyroxenes from cumulate mafic enclaves hosted in cogenetic dacitic lavas of the 1570-1573 and 1925-1928 eruptions of Nea Kameni. These unique data on Aegean volcanism were compared with those of gases collected in quiescent periods and during the unrest. The 3He/4He ratios (3.1-4.0 Ra) are significantly lower than the typical arc-volcano values (R/Ra ∼ 7-8), suggesting the occurrence of magma contamination in Santorini plumbing system, which would further modify the 3He/4He ratio of parental magmas generated in the local metasomatized mantle. The 3He/4He values of enclaves (3.1-3.6 Ra) are comparable to those measured in gases during quiescent periods, confirming that enclaves reflect the He-isotope signature of magma residing at shallow depths and feeding passive degassing. A significant increase in soil CO2 flux from Nea Kameni and anomalous compositional variations in the fumaroles were identified during the unrest, accordingly with previous studies. Simultaneously, 3He/4He ratios up to 4.0 Ra were also measured, demonstrating that the unrest was due to the intrusion into the shallow plumbing system of a more-primitive 3He-rich magma, which is even volatile richer and less contaminated than mafic magma erupted as enclaves. This new intrusion did not however trigger an eruption.

Background: Genome reduction in intracellular pathogens and endosymbionts is usually compensated by reliance on the host for energy and nutrients. Free-living taxa with reduced genomes must however evolve strategies for generating functional diversity to support their independent lifestyles. An emerging model for the latter case is the Rhodophyta (red algae) that comprises an ecologically widely distributed, species-rich phylum. Red algae have undergone multiple phases of significant genome reduction, including extremophilic unicellular taxa with limited nuclear gene inventories that must cope with hot, highly acidic environments. Results: Using genomic data from eight red algal lineages, we identified 155 spliceosomal machinery (SM)-associated genes that were putatively present in the red algal common ancestor. This core SM gene set is most highly conserved in Galdieria species (150 SM genes) and underwent differing levels of gene loss in other examined red algae (53-145 SM genes). Surprisingly, the high SM conservation in Galdieria sulphuraria coincides with the enrichment of spliceosomal introns in this species (2 introns/gene) in comparison to other red algae (<0.34 introns/gene). Spliceosomal introns in G. sulphuraria undergo alternatively splicing, including many that are differentially spliced upon changes in culture temperature. Conclusions: Our work reveals the unique nature of G. sulphuraria among red algae with respect to the conservation of the spliceosomal machinery and introns. We discuss the possible implications of these findings in the highly streamlined genome of this free-living eukaryote.

Street trees are an important part of urban vegetation due to their provisioning of different types of ecosystem services such as local climate regulation and contribution to aesthetical and recreational values. In order to provide these services, urban trees need to endure many stress factors not present in natural environments, such as the widespread use of impervious surfaces in the vicinity of street trees. However, few studies have evaluated the effect of this potential stress factor on urban tree growth. The aim of this study was therefore to investigate how ground surface permeability affects stem and current-year shoot growth of linden (Tilia europaea) street trees in Gothenburg, Sweden. We found that a small fraction of permeable ground surface in the vertically projected tree crown area caused lower stem growth and strongly suppressed current-year shoot growth. This finding can guide future city planning, demonstrating that the vitality of street trees is compromised when the permeable surface area in the vicinity of the tree is small.

Street trees are an important part of urban vegetation due to their provisioning of different types of ecosystem services such as local climate regulation and contribution to aesthetical and recreational values. In order to provide these services, urban trees need to endure many stress factors not present in natural environments, such as the widespread use of impervious surfaces in the vicinity of street trees. However, few studies have evaluated the effect of this potential stress factor on urban tree growth. The aim of this study was therefore to investigate how ground surface permeability affects stem and current-year shoot growth of linden (Tilia europaea) street trees in Gothenburg, Sweden. We found that a small fraction of permeable ground surface in the vertically projected tree crown area caused lower stem growth and strongly suppressed current-year shoot growth. This finding can guide future city planning, demonstrating that the vitality of street trees is compromised when the permeable surface area in the vicinity of the tree is small.

Background: Genome reduction in intracellular pathogens and endosymbionts is usually compensated by reliance on the host for energy and nutrients. Free-living taxa with reduced genomes must however evolve strategies for generating functional diversity to support their independent lifestyles. An emerging model for the latter case is the Rhodophyta (red algae) that comprises an ecologically widely distributed, species-rich phylum. Red algae have undergone multiple phases of significant genome reduction, including extremophilic unicellular taxa with limited nuclear gene inventories that must cope with hot, highly acidic environments. Results: Using genomic data from eight red algal lineages, we identified 155 spliceosomal machinery (SM)-associated genes that were putatively present in the red algal common ancestor. This core SM gene set is most highly conserved in Galdieria species (150 SM genes) and underwent differing levels of gene loss in other examined red algae (53-145 SM genes). Surprisingly, the high SM conservation in Galdieria sulphuraria coincides with the enrichment of spliceosomal introns in this species (2 introns/gene) in comparison to other red algae (<0.34 introns/gene). Spliceosomal introns in G. sulphuraria undergo alternatively splicing, including many that are differentially spliced upon changes in culture temperature. Conclusions: Our work reveals the unique nature of G. sulphuraria among red algae with respect to the conservation of the spliceosomal machinery and introns. We discuss the possible implications of these findings in the highly streamlined genome of this free-living eukaryote.

The Greek region is characterized by intense geodynamic activity with widespread volcanic, geothermal and seismic activity. Its complex geology is reflected in the large variety of chemical and isotopic composition of its gas manifestations. Basing on their chemical composition the gases can be subdivided in three groups, respectively CO2, CH4 or N2-dominated. On oxygen-free basis these three gases make up more than 97% of the total composition. The only exceptions are fumarolic gases of Nisyros that contain substantial amounts of H2S (up to more than 20%) and one sample of Milos that contains 15% of H2. CO2-dominated gases with clear mantle contribution in their He isotopic composition (R/Ra corrected for air contamination ranging from 0.5 to 5.7) are found along the subduction-related south Aegean active volcanic arc and on the Greek mainland close to recent (upper Miocene to Pleistocene) volcanic centers. These areas are generally characterized by active or recent extensive tectonic activity and high geothermal gradients. On the contrary, gases sampled in the more external nappes of the Hellenide orogen have generally a CH4- or N2-rich compositions and helium isotope composition with a dominant crustal contribution (R/Ra corr < 0.2). The chemical and isotopic characteristics of the emitted gas display therefore a clear relationship with the different geodynamic sectors of the region. Gas geochemistry of the area contributes to a better definition of the crust-mantle setting of the Hellenic region.

Cyanidioschyzon merolae (C. merolae) is an acidophilic red alga growing in a naturally low carbon dioxide (CO2) environment. Although it uses a ribulose 1,5-bisphosphate carboxylase/oxygenase with high affinity for CO2, the survival of C. merolae relies on functional photorespiratory metabolism. In this study, we quantified the transcriptomic response of C. merolae to changes in CO2 conditions. We found distinct changes upon shifts between CO2 conditions, such as a concerted up-regulation of photorespiratory genes and responses to carbon starvation. We used the transcriptome data set to explore a hypothetical CO2 concentrating mechanism in C. merolae, based on the assumption that photorespiratory genes and possible candidate genes involved in a CO2 concentrating mechanism are co-expressed. A putative bicarbonate transport protein and two a-carbonic anhydrases were identified, which showed enhanced transcript levels under reduced CO2 conditions. Genes encoding enzymes of a PEPCK-type C-4 pathway were co-regulated with the photorespiratory gene cluster. We propose a model of a hypothetical low CO2 compensation mechanism in C. merolae integrating these low CO2-inducible components.

Methylglyoxal (MGO) and glyoxal (GO) are toxic reactive carbonyl species generated as by-products of glycolysis. The pre-emption pathway for detoxification of these products, the glyoxalase (GLX) system, involves two consecutive reactions catalyzed by GLXI and GLXII. In Arabidopsis thaliana, the GLX system is encoded by three homologs of GLXI and three homologs of GLXII, from which several predicted GLXI and GLXII isoforms can be derived through alternative splicing. We identified the physiologically relevant splice forms using sequencing data and demonstrated that the resulting isoforms have different subcellular localizations. All three GLXI homologs are functional in vivo, as they complemented a yeast GLXI loss-of-function mutant. Efficient MGO and GO detoxification can be controlled by a switch in metal cofactor usage. MGO formation is closely connected to the flux through glycolysis and through the Calvin Benson cycle; accordingly, expression analysis indicated that GLXI is transcriptionally regulated by endogenous sugar levels. Analyses of Arabidopsis loss-of-function lines revealed that the elimination of toxic reactive carbonyl species during germination and seedling establishment depends on the activity of the cytosolic GLXI; 3 isoform. The Arabidopsis GLX system involves the cytosol, chloroplasts, and mitochondria, which harbor individual components that might be used at specific developmental stages and respond differentially to cellular sugar status.

The study area is close to the boundary of three tectonic plates (Anatolian, Arabian, and African plates) and is characterized by important tectonic lineaments, which consist mainly of the Dead Sea Fault (DSF), the Karasu Fault, and the East Anatolian Fault (EAF) systems. To understand the origin of soil gas emanation and its relationships with the tectonics of the Amik Basin (Hatay), a detailed soil gas sampling was systematically performed. Together with CO2 flux measurements, > 220 soil gas samples were analyzed for Rn and CO2 concentrations. The distribution of soil Rn (kBq/m3), CO2 concentration (ppm), and CO2 flux (g/m2/day) in the area appears as a point source (spot) and/or diffuses (halo) anomalies along the buried faults/fractures due to crustal leaks. The results revealed that Rn and CO2 concentrations in the soil gas show anomalous values at the specific positions in the Amik Basin. The trace of these anomalous values is coincident with the N-S trending DSF. CO2 is believed to act as a carrier for Rn gas. Based on the Rn and CO2 concentrations of soil gases, at least three gas components are required to explain the observed variations. In addition to the atmospheric component, two other gas sources can be recognized. One is the deep crust component, which exhibits high Rn and CO2 concentrations, and is considered the best indicator for the surface location of fault/fracture zones in the region. The other component is a shallower gas source with high Rn concentration and low CO2 concentration. Moreover, He isotopic compositions of representative samples vary from 0.94 to 0.99 Ra, illustrating that most samples have a soil air component and may have mixed with some crustal component, without significant input of the mantle component. Based on the repeated measurements at a few sites, soil gas concentrations at the same site were observed to be higher in 2014 than in 2013, which may be associated with the activity of the DSF in 2013–2014. This suggests that

Cyanidioschyzon merolae (C. merolae) is an acidophilic red alga growing in a naturally low carbon dioxide (CO2) environment. Although it uses a ribulose 1,5-bisphosphate carboxylase/oxygenase with high affinity for CO2, the survival of C. merolae relies on functional photorespiratory metabolism. In this study, we quantified the transcriptomic response of C. merolae to changes in CO2 conditions. We found distinct changes upon shifts between CO2 conditions, such as a concerted up-regulation of photorespiratory genes and responses to carbon starvation. We used the transcriptome data set to explore a hypothetical CO2 concentrating mechanism in C. merolae, based on the assumption that photorespiratory genes and possible candidate genes involved in a CO2 concentrating mechanism are co-expressed. A putative bicarbonate transport protein and two a-carbonic anhydrases were identified, which showed enhanced transcript levels under reduced CO2 conditions. Genes encoding enzymes of a PEPCK-type C-4 pathway were co-regulated with the photorespiratory gene cluster. We propose a model of a hypothetical low CO2 compensation mechanism in C. merolae integrating these low CO2-inducible components.

Methylglyoxal (MGO) and glyoxal (GO) are toxic reactive carbonyl species generated as by-products of glycolysis. The pre-emption pathway for detoxification of these products, the glyoxalase (GLX) system, involves two consecutive reactions catalyzed by GLXI and GLXII. In Arabidopsis thaliana, the GLX system is encoded by three homologs of GLXI and three homologs of GLXII, from which several predicted GLXI and GLXII isoforms can be derived through alternative splicing. We identified the physiologically relevant splice forms using sequencing data and demonstrated that the resulting isoforms have different subcellular localizations. All three GLXI homologs are functional in vivo, as they complemented a yeast GLXI loss-of-function mutant. Efficient MGO and GO detoxification can be controlled by a switch in metal cofactor usage. MGO formation is closely connected to the flux through glycolysis and through the Calvin Benson cycle; accordingly, expression analysis indicated that GLXI is transcriptionally regulated by endogenous sugar levels. Analyses of Arabidopsis loss-of-function lines revealed that the elimination of toxic reactive carbonyl species during germination and seedling establishment depends on the activity of the cytosolic GLXI; 3 isoform. The Arabidopsis GLX system involves the cytosol, chloroplasts, and mitochondria, which harbor individual components that might be used at specific developmental stages and respond differentially to cellular sugar status.

The study area is close to the boundary of three tectonic plates (Anatolian, Arabian, and African plates) and is characterized by important tectonic lineaments, which consist mainly of the Dead Sea Fault (DSF), the Karasu Fault, and the East Anatolian Fault (EAF) systems. To understand the origin of soil gas emanation and its relationships with the tectonics of the Amik Basin (Hatay), a detailed soil gas sampling was systematically performed. Together with CO2 flux measurements, > 220 soil gas samples were analyzed for Rn and CO2 concentrations. The distribution of soil Rn (kBq/m3), CO2 concentration (ppm), and CO2 flux (g/m2/day) in the area appears as a point source (spot) and/or diffuses (halo) anomalies along the buried faults/fractures due to crustal leaks. The results revealed that Rn and CO2 concentrations in the soil gas show anomalous values at the specific positions in the Amik Basin. The trace of these anomalous values is coincident with the N-S trending DSF. CO2 is believed to act as a carrier for Rn gas. Based on the Rn and CO2 concentrations of soil gases, at least three gas components are required to explain the observed variations. In addition to the atmospheric component, two other gas sources can be recognized. One is the deep crust component, which exhibits high Rn and CO2 concentrations, and is considered the best indicator for the surface location of fault/fracture zones in the region. The other component is a shallower gas source with high Rn concentration and low CO2 concentration. Moreover, He isotopic compositions of representative samples vary from 0.94 to 0.99 Ra, illustrating that most samples have a soil air component and may have mixed with some crustal component, without significant input of the mantle component. Based on the repeated measurements at a few sites, soil gas concentrations at the same site were observed to be higher in 2014 than in 2013, which may be associated with the activity of the DSF in 2013–2014. This suggests that

This study is focused on the (micro)biogeochemical features of two close geothermal sites (FAV1 and FAV2), both selected at the main exhalative area of Pantelleria Island, Italy. A previous biogeochemical survey revealed high CH4 consumption and the presence of a diverse community of methanotrophs at FAV2 site, whereas the close site FAV1 was apparently devoid of methanotrophs and recorded no CH4 consumption. Next-Generation Sequencing (NGS) techniques were applied to describe the bacterial and archaeal communities which have been linked to the physicochemical conditions and the geothermal sources of energy available at the two sites. Both sites are dominated by Bacteria and host a negligible component of ammonia-oxidizing Archaea (phylum Thaumarchaeota). The FAV2 bacterial community is characterized by an extraordinary diversity of methanotrophs, with 40% of the sequences assigned to Methylocaldum, Methylobacter (Gammaproteobacteria) and Bejerickia (Alphaproteobacteria); conversely, a community of thermo-acidophilic chemolithotrophs (Acidithiobacillus, Nitrosococcus) or putative chemolithotrophs (Ktedonobacter) dominates the FAV1 community, in the absence of methanotrophs. Since physical andchemical factors of FAV1, such as temperature and pH, cannot be considered limiting for methanotrophy, it is hypothesized that the main limiting factor for methanotrophs could be high NH4(+) concentration. At the same time, abundant availability of NH4(+) and other high energy electron donors and acceptors determined by the hydrothermal flux in this site create more energetically favourable conditions for chemolithotrophs that outcompete methanotrophs in non-nitrogen-limited soils.

The Kizildag and Erzin (Hatay) ophiolite bodies are an extension of the peri-Arabian ophiolite belt that includes the Troodos (Cyprus), Baër- Bassit (Syria) and Semail (Oman) ophiolites in the Eastern Mediterranean Region which genetically and tectonically belong to the Southern Tethys oceanic lithosphere (Sengör and Yilmaz, 1981). This study aims to understand the chemical and isotopic characteristics of bubbling and dissolved gases of the hyperalkaline waters related to the serpentinization process in ultramafic rocks at the Amik Basin (Hatay-Turkey) and compare them with the remnants of the peri-Arabian ophiolite belt. The Amik Basin is seismically very active and many catastrophic earthquakes hit the area at historical times due to the Dead Sea Transform and Karasu Faults which further north join to the East Anatolian Fault (Mahmoud et al., 2013). The basin is very close to the triple junction point with the tectonic lineaments connecting the Anatolian, Arabian and African plates. Around 23 dry seeps, free and dissolved gas samples were taken from the study area and analyzed their chemical and isotopic composition. Three main groups of groundwater have been recognized in the area: i)Low salinity and pH between 6 and 9 (shallow groundwater), ii)High salinity and pH between 7 and 8 (deep groundwater), iii) Low salinity and pH between 10 and 12 (groundwater circulating in the ophiolites).Because of serpentinisation processes, many hyper-alkaline springs(pH> 9 up to 12.2)are found in the area. Hyper-alkaline springs flow through the creeks along the narrow valleys, having low yields and are characterized by snow-like deposits due to the precipitation of brucite and hydrotalcite. The study shows a great variability in the gas composition of the fluids circulating in the Kizildag ophiolite complex. All gases show very low CO2 and O2 concentrations and their composition is dominated either by H2 or CH4 or N2. He isotopic composition reveals a mixing trend between atmos

Highlights • The complex geodynamic structure of the area is reflected in the wide range of compositions of the emitted fluids. • High salinity waters with hydrocarbon gases and a purely crustal He component were collected from deep wells. • Hyperalkaline waters with CH4- and H2-dominated gases are found in the ophiolite complex. • Shallow meteoric groundwaters in the southern part of the basin show a prevailing atmospheric component for dissolved gases. • A significant mantle component (He and C) is found in the dissolved gases of the northeastern sites. Abstract We investigated the geochemical features of the fluids circulating over the Amik Basin (SE Turkey–Syria border), which is crossed by the Northern extension of the DSF (Dead Sea Fault) and represents the boundary area of three tectonic plates (Anatolian, Arabian and African plates). We collected 34 water samples (thermal and cold from natural springs and boreholes) as well as 8 gas samples (bubbling and gas seepage) besides the gases dissolved in the sampled waters. The results show that the dissolved gas phase is a mixture of shallow (atmospheric) and deep components either of mantle and crustal origin. Coherently the sampled waters are variable mixtures of shallow and deep ground waters, the latter being characterised by higher salinity and longer residence times. The deep groundwaters (from boreholes deeper than 1000 m) have a CH4-dominated dissolved gas phase related to the presence of hydrocarbon reservoirs. The very unique tectonic setting of the area includes the presence of an ophiolitic block outcropping in the westernmost area on the African Plate, as well as basalts located to the North and East on the Arabic Plate. The diffuse presence of CO2-enriched gases, although diluted by the huge groundwater circulation, testifies a regional degassing activity. Fluids circulating over the ophiolitic block are marked by H2-dominated gases with abiogenic methane and high-pH waters. The measured 3He/4He isot

Highlights • The complex geodynamic structure of the area is reflected in the wide range of compositions of the emitted fluids. • High salinity waters with hydrocarbon gases and a purely crustal He component were collected from deep wells. • Hyperalkaline waters with CH4- and H2-dominated gases are found in the ophiolite complex. • Shallow meteoric groundwaters in the southern part of the basin show a prevailing atmospheric component for dissolved gases. • A significant mantle component (He and C) is found in the dissolved gases of the northeastern sites. Abstract We investigated the geochemical features of the fluids circulating over the Amik Basin (SE Turkey–Syria border), which is crossed by the Northern extension of the DSF (Dead Sea Fault) and represents the boundary area of three tectonic plates (Anatolian, Arabian and African plates). We collected 34 water samples (thermal and cold from natural springs and boreholes) as well as 8 gas samples (bubbling and gas seepage) besides the gases dissolved in the sampled waters. The results show that the dissolved gas phase is a mixture of shallow (atmospheric) and deep components either of mantle and crustal origin. Coherently the sampled waters are variable mixtures of shallow and deep ground waters, the latter being characterised by higher salinity and longer residence times. The deep groundwaters (from boreholes deeper than 1000 m) have a CH4-dominated dissolved gas phase related to the presence of hydrocarbon reservoirs. The very unique tectonic setting of the area includes the presence of an ophiolitic block outcropping in the westernmost area on the African Plate, as well as basalts located to the North and East on the Arabic Plate. The diffuse presence of CO2-enriched gases, although diluted by the huge groundwater circulation, testifies a regional degassing activity. Fluids circulating over the ophiolitic block are marked by H2-dominated gases with abiogenic methane and high-pH waters. The measured 3He/4He isot