Sulfidic Springs Research Articles

Effects of plasticity and genetic divergence in phenotypic trait expression of sulfide spring fishes

Effects of plasticity and genetic divergence in phenotypic trait expression of sulfide spring fishes

Evolutionary Rate Shifts in Coding and Regulatory Regions Underpin Repeated Adaptation to Sulfidic Streams in Poeciliid Fishes.

Adaptation to extreme environments often involves the evolution of dramatic physiological changes. To better understand how organisms evolve these complex phenotypic changes, the repeatability and predictability of evolution, and possible constraints on adapting to an extreme environment, it is important to understand how adaptive variation has evolved. Poeciliid fishes represent a particularly fruitful study system for investigations of adaptation to extreme environments due to their repeated colonization of toxic hydrogen sulfide-rich springs across multiple species within the clade. Previous investigations have highlighted changes in the physiology and gene expression in specific species that are thought to facilitate adaptation to hydrogen sulfide-rich springs. However, the presence of adaptive nucleotide variation in coding and regulatory regions and the degree to which convergent evolution has shaped the genomic regions underpinning sulfide tolerance across taxa are unknown. By sampling across seven independent lineages in which nonsulfidic lineages have colonized and adapted to sulfide springs, we reveal signatures of shared evolutionary rate shifts across the genome. We found evidence of genes, promoters, and putative enhancer regions associated with both increased and decreased convergent evolutionary rate shifts in hydrogen sulfide-adapted lineages. Our analysis highlights convergent evolutionary rate shifts in sulfidic lineages associated with the modulation of endogenous hydrogen sulfide production and hydrogen sulfide detoxification. We also found that regions with shifted evolutionary rates in sulfide spring fishes more often exhibited convergent shifts in either the coding region or the regulatory sequence of a given gene, rather than both.

Biodiversity Survey of Hydrogen Sulfide Thermal Springs in Dagestan Using 16S Metabarcoding

The Greater Caucasus region is rich in thermal hydrogen sulfide springs, but their microbiological composition is poorly studied. In this study, using high-throughput profiling of the V4 region of the 16S rRNA gene, we analyzed the microbial communities of such springs in the Republic of Dagestan, assessed their biodiversity, and investigated correlations between abiotic factors and microbial community composition. Results show that the alpha diversity of microbial communities is negatively correlated with temperature and pH, with community composition being significantly influenced by the presence of hydrocarbons, redox potential, and dissolved organic matter content. The springs near the village of Kayakent were distinguished by unique physicochemical parameters, and their microbial communities were characterized by high taxonomic novelty, dominated by uncultivated representatives of the families Arcobacteraceae and Hydrogenophilaceae.

TilS and rpoB: New Molecular Markers for Phylogenetic and Biodiversity Studies of the Genus Thiothrix.

Currently, the phylogeny of the genus Thiothrix is based on comparative whole genome analysis because of the high homology of the 16S ribosomal RNA gene sequences within the genus. We analyzed the possibility of using various conservative genes as phylogenetic markers for the genus Thiothrix. We found that the levels of similarity of the nucleotide sequences of the tRNA(Ile)-lysidine synthase (tilS) and the β subunit of RNA polymerase (rpoB) genes are in good agreement with the average nucleotide identity (ANI) values between the genomes of various representatives of the genus Thiothrix. The genomes of Thiothrix strains MK1, WS, DNT52, DNT53, and H33 were sequenced. Taxonomic analysis using both whole genomes and the tilS gene consistently showed that MK1 and WS belong to Thiothrix lacustris, while DNT52, DNT53, and H33 belong to Thiothrix subterranea. The tilS gene fragments were subjected to high-throughput sequencing to profile the Thiothrix mat of a sulfidic spring, which revealed the presence of known species of Thiothrix and new species-level phylotypes. Thus, the use of tilS and rpoB as phylogenetic markers will allow for rapid analyses of pure cultures and natural communities for the purpose of phylogenetic identification of representatives of the genus Thiothrix.

Bacterial Communities in a Gradient of Abiotic Factors Near a Sulfide Thermal Spring in Northern Baikal

The structure and diversity of microbial communities developing in the combined gradient of temperature (44–19 °C), as well as concentration of oxygen (0–10 mg/L) and hydrogen sulfide (33–0.7 mg/L), were studied in the thermal sulfide spring on the coast of Northern Lake Baikal. The predominance of bacteria participating in sulfur and nitrogen cycles and significant changes in the composition of microbial communities were noted at changing physicochemical conditions. Thiovirga sp. (sulfur-oxidizing bacteria, up to 37%) and Azonexus sp. (nitrogen-fixing bacteria, up to 43%) were dominant at high temperatures and concentrations of hydrogen sulfide in two hydrotherms. In addition, a significant contribution of the Rhodocyclaceae family (up to 51%) which is involved in the denitrification processes, and Acetoanaerobium sp. (up to 20%) fixing carbon oxide were found in the spring water. In the stream, mainly oxygenic cyanobacteria (up to 56%) developed at a temperature of 33 °C, in the presence of hydrogen sulfide and oxygen. In addition, sulfur bacteria of the genus Thiothrix (up to 48%) found in epibiotic communities of benthic animals of Lake Baikal were present here. Thiothrix sp. formed massive fouling in the zone of mixing lake and thermal waters with a significant contribution of hydrogen-oxidizing bacteria of the genus Hydrogenophaga (up to 22.5%). As well as chemolitho- and phototrophic bacteria, chemoorganotrophs (phyla Firmicutes, Chloroflexi, Desulfobacterota, Nitrospirota, Fibrobacterota, etc.) have been identified in all communities. The chemical parameters of water in spring and coastal zones indicate a significant change in the composition of thermal waters occurring with the participation of diverse microbial communities that contribute to the assimilation of inorganic components of mineral thermal waters.

Unique Populations of Sulfur-Oxidizing Bacteria in Natural Cold Sulfur Springs in Slovakia

Currently, there are over 200 officially registered sulfur springs in Slovakia, most of which are cold hydrogen sulfide springs with a characteristic strong odor of rotten eggs. Their typical inhabitants are filamentous sulfur-oxidizing bacteria. The aim of this study was to identify the major bacterial populations inhabiting sulfur springs in Slovakia using a combination of non-cultivation and cultivation approaches. Non-cultivation analyses revealed high variability of sulfur-oxidizing bacteria in Slovak springs. Sulfur mats were usually dominated by chemolithotrophic sulfur-oxidizers from the phylum Proteobacteria (more than 87%), followed by photoautotrophic sulfur-oxidizers of the phylum Chlorobi. The group of nonsulfur-oxidizers was composed of typical freshwater species and bacteria with genetic potential for sulfur oxidation. The low similarity in the 16S rRNA gene sequence of the sequenced DGGE bands indicates that about half of the sulfur-oxidizing bacteria identified represent new species/genera of sulfur-oxidizing bacteria. In attempts to cultivate potential new species of sulfur-oxidizing bacteria, a very low overlap was observed between non-cultivation and cultivation analyses, and a new species of the Thiofaba genus was cultivated. Our results expand knowledge on the diversity of sulfur bacteria in cold sulfur springs in Slovakia and indicate that the diversity of sulfur-oxidizing bacteria is significantly underestimated and that sulfur springs could be inhabited by unique bacterial populations.

Study of dilution processes of sulfidic aquifer hosted by the Fiume-Vento karstic complex, Frasassi (Central Italy)

Sulfuric acid caves are widespread worldwide. In Central Italy, the Fiume-Vento karstic complex represents the most important active hypogenic cave system hosting several interconnected lakes where groundwater moves towards sulfidic springs emerging along the Sentino Stream. Stratification and dilution phenomena between freshwater and sulfidic water occur in many underground lakes, even if they remain still open if these processes are driven by stream-aquifer interaction or dripping water. The speleological knowledge coupled with geochemical surveys can help study groundwater circulation in the karst system’s inner and outer portions. The geochemical analyses on water samples taken along the Sentino Stream, inside the caves (dripping and lakes water) and in sulfidic springs allow establishing the origin of the dilution water in the dripping water. However, stream-aquifer interactions cannot be excluded during flood events. Using the tracer masse balance method (chloride and sodium ions), the discharge of the sulfidic springs ranges between 65 and 11 L/s. The results presented in this study may help understand groundwater circulation and dilution phenomena in other karst systems characterised by sulfuric acid speleogenesis type.

Earthworms (Oligochaeta, Lumdricidae) in the Komi Republic

The article presents information about 11 species in 8 genera of earthworms (Oligochaeta, Lumbricidae) in the Komi Republic. They belong to three morpho-ecological groups inhabiting different soil horizons (litter, litter/soil, soil). The species distribution maps have been compiled. The density of each species and their habitat affiliations in different flatland subzones and altitudinal zones of the Ural Mountains are shown. The number of species tends to decline in a regular manner from southern taiga to shrub tundra, from the Northern to Polar Urals. Boreal zone soils are inhabited by members of the genera Aporrectodea, Dendrobaena, Bimastos, Eisenia, Eiseniella, Lumbricus, Octolasion. Four species: Aporrectodea caliginosa, A. rosea, Eisenia fetida, and Octolasion lacteum, prefer meadows and farmlands. The species Bimastos rubidus and Eiseniella tetraedra inhabit meadows, willow carrs and forests in southern and middle taiga; they are absent in the extremely northern taiga and forest tundra; their habitats in the tundra zone are hydrogen sulfide springs. Three species (Dendrobaena octaedra, Eisenia nordenskioldi, Lumbricus rubellus) have been found in all natural zones and subzones. They compose the Lumbricidae fauna in the tundra zone. Northern Urals harbored the same earthworm species as the boreal zone. Two more species, Rhiphaeodrilus diplotetrathecus and Eisenia atlavinyteae, are representatives of the montane Urals Lumbricidae complex. Five species: R. diplotetrathecus, D. octaedra, E. nordenskioldi, L. rubellus, and O. lacteum, are known for the Subpolar Urals. The species D. octaedra, E. nordenskioldi, L. rubellus have been detected in the Polar Urals as in the tundra zone. The altitudinal distribution of earthworms in the Urals is characterized by the presence of ‘soil’ species in the montane forest zone and a decline in the species diversity in the subalpine and alpine tundra zones, mostly at the expense of the litter/soil group

Two New Species of Filamentous Sulfur Bacteria of the Genus Thiothrix, Thiothrix winogradskyi sp. nov. and 'Candidatus Thiothrix sulfatifontis' sp. nov.

The metagenome of foulings from sulfidic spring “Serovodorodny” (Tatarstan, Russia), where members of the genus Thiothrix was observed, was sequenced. Representatives of the phyla Gammaproteobacteria, Cyanobacteria and Campilobacteriota dominated in the microbial community. The complete genome of Thiothrix sp. KT was assembled from the metagenome. It displayed 93.93–99.72% 16S rRNA gene sequence identity to other Thiothrix species. The average nucleotide identity (ANI) и digital DNA-DNA hybridization (dDDH) showed that the genome designated KT represents a new species within the genus Thiothrix, ‘Candidatus Thiothrix sulfatifontis’ sp. nov. KT. The taxonomic status has been determined of the strain Thiothrix sp. CT3, isolated about 30 years ago and not assigned to any of Thiothrix species due to high 16S rRNA gene sequence identity with related species (i.e., 98.8–99.4%). The complete genome sequence of strain CT3 was determined. The ANI between CT3 and other Thiothrix species was below 82%, and the dDDH values were less than 40%, indicating that strain CT3 belongs to a novel species, Thiothrix winogradskyi sp. nov. A genome analysis showed that both strains are chemo-organoheterotrophs, chemolithotrophs (in the presence of hydrogen sulfide and thiosulfate) and chemoautotrophs. For the first time, representatives of Thiothrix showed anaerobic growth in the presence of thiosulfate.

Emerging Ecotone and Microbial Community of a Sulfidic Spring in the Reka River near Škocjanske Jame, Slovenia

During long periods with no precipitation, a sulfidic spring (Smrdljivec) appears in the dry bed of the Reka River before sinking into the karst underground. The study characterizes the area’s geological setting, development of microbial communities and an ecotone, and impact on the vulnerable karst ecosystem. Geological mapping of the area, stable isotopic analyses, field measurements, and physico-chemical and toxicity analyses were applied to elucidate the environmental conditions. The spring’s microbial diversity was assessed using cultivation methods, microscopy, and metagenomics. Sulfur compounds in the spring probably originate from coal layers in the vicinity. Metagenomic analyses revealed 175 distinct operational taxonomic units in spring water and biofilms. Proteobacteria predominated in developed biofilms, and a “core” microbiome was represented by methylotrophs, including Methylobacter, Methylomonas, and Methylotenera. Diatoms represented an important component of biofilm biomass. A combination of environmental factors and climatic conditions allows the formation and accessibility of emerging biodiversity hotspots and ecotones. Details of their dynamic nature, global impact, and distribution should be highlighted further and given more protection.

Comparative Genome Analysis of the Genus Thiothrix Involving Three Novel Species, Thiothrix subterranea sp. nov. Ku-5, Thiothrix litoralis sp. nov. AS and "Candidatus Thiothrix anitrata" sp. nov. A52, Revealed the Conservation of the Pathways of Dissimilatory Sulfur Metabolism and Variations in the Genetic Inventory for Nitrogen Metabolism and Autotrophic Carbon Fixation.

Two strains of filamentous, colorless sulfur bacteria were isolated from bacterial fouling in the outflow of hydrogen sulfide-containing waters from a coal mine (Thiothrix sp. Ku-5) and on the seashore of the White Sea (Thiothrix sp. AS). Metagenome-assembled genome (MAG) A52 was obtained from a sulfidic spring in the Volgograd region, Russia. Phylogenetic analysis based on the 16S rRNA gene sequences showed that all genomes represented the genus Thiothrix. Based on their average nucleotide identity and digital DNA-DNA hybridization data these new isolates and the MAG represent three species within the genus Thiothrix with the proposed names Thiothrix subterranea sp. nov. Ku-5T, Thiothrix litoralis sp. nov. AST, and “Candidatus Thiothrix anitrata” sp. nov. A52. The complete genome sequences of Thiothrix fructosivorans QT and Thiothrix unzii A1T were determined. Complete genomes of seven Thiothrix isolates, as well as two MAGs, were used for pangenome analysis. The Thiothrix core genome consisted of 1,355 genes, including ones for the glycolysis, the tricarboxylic acid cycle, the aerobic respiratory chain, and the Calvin cycle of carbon fixation. Genes for dissimilatory oxidation of reduced sulfur compounds, namely the branched SOX system (SoxAXBYZ), direct (soeABC) and indirect (aprAB, sat) pathways of sulfite oxidation, sulfur oxidation complex Dsr (dsrABEFHCEMKLJONR), sulfide oxidation systems SQR (sqrA, sqrF), and FCSD (fccAB) were found in the core genome. Genomes differ in the set of genes for dissimilatory reduction of nitrogen compounds, nitrogen fixation, and the presence of various types of RuBisCO.

Dominance of Arcobacter in the white filaments from the thermal sulfidic spring of Fetida Cave (Apulia, southern Italy)

The thermal spring of Fetida Cave, a still active sulfuric acid cave opening at sea level and located in Santa Cesarea Terme, southeastern Salento (Apulia region, Southern Italy) hosts abundant floating white filaments. The white filaments were mainly composed of sulfur crystals surrounded by microbial mass of the phyla Epsilonbacteraeota, Proteobacteria, Bacteroidetes, and Patescibacteria. The most abundant genus in the white filaments collected from the waters in the innermost part of the cave dominated by sulfidic exhalations was Arcobacter. This abundance can be related to the higher concentration of sulfide dissolved in water, and low oxygen and pH values. Conversely, lower Arcobacter abundances were obtained in the filaments collected in the entrance and middle part of the cave, where sulfidic water mixes with seawater, as the cave is subjected to tides and the mixing of fresh (continental) with marine water. The geochemical analysis of water and atmospheric gases confirmed these environmental constraints. In fact, the highest concentrations of H2S in the air and water were recorded closest to the spring upwelling in the innermost part of the cave, and the lowest ones near the cave entrance. The metabolic versatility of Arcobacter might provide a competitive advantage in the colonization of water bodies characterized by high sulfide, low oxygen, and dynamic fluid movement.

Acoustic and visual stimuli combined promote stronger responses to aerial predation in fish.

Bird predation poses a strong selection pressure on fish. Since birds must enter the water to catch fish, a combination of visual and mechano-acoustic cues (multimodal) characterize an immediate attack, while single cues (unimodal) may represent less dangerous disturbances. We investigated whether fish could use this information to distinguish between non-threatening and dangerous events and adjust their antipredator response to the perceived level of risk. To do so, we investigated the antipredator behavior of the sulphur molly (Poecilia sulphuraria), a small freshwater fish which is almost exclusively preyed on by piscivorous birds in its endemic sulfide spring habitat. In a field survey, we confirmed that these fish frequently have to distinguish between disturbances stemming from attacking birds (multimodal) and those which pose no (immediate) threat such as bird overflights (unimodal). In a laboratory experiment, we then exposed fish to artificial visual and/or acoustic stimuli presented separately or combined. Sensitivity was high regardless of stimulus type and number (more than 96% of fish initiated diving), but fish dove deeper, faster, and for longer when both stimuli were available simultaneously. Based on the system’s high rates of bird activity, we argue that such an unselective dive initiation with subsequent fine-tuning of diving parameters in accordance to cue modality represents an optimal strategy for these fish to save energy necessary to respond to future attacks. Ultimately, our study shows that fish anticipate the imminent risk posed by disturbances linked to bird predation through integrating information from both visual and acoustic cues.

Ubiquity of Euglena mutabilis Population in Three Ecologically Distinct Acidic Habitats in Southwestern Japan

Three strains of Euglena mutabilis were isolated from sediments in acidic inland water systems (pH = 3.4–4.7), in Southwestern Japan—acid mine drainage in Sensui (Fukuoka), cold sulfidic spring in Bougatsuru (Oita), and a temporal pool in the Ebinokogen volcanic area (Miyazaki). All strains grew well in acidic media at pH 3.07. Phylogenetic analysis among these three strains showed high similarities to plastid SSU and nuclear SSU rRNA gene sequences (99.86% and 99.76%, respectively). They were closely related to the cultured isolates from other highly acidic habitats (pH = 2.0–5.9). Concentration of sulfate, aluminum, calcium, and iron had 7–70 fold of differences among the three studied habitats. Our results imply that the rRNA genes of E. mutabilis have compensated for their low genetic diversity by adapting to a wide pH range, as well as various water chemistry of habitats.

Diurnal Changes in Hypoxia Shape Predator-Prey Interaction in a Bird-Fish System

Animals often face changing environments, and behavioral flexibility allows them to rapidly and adaptively respond to abiotic factors that vary more or less regularly. However, abiotic factors that affect prey species do not necessarily affect their predators. Still, the prey’s response might affect the predator indirectly, yet evidence from the wild for such a classical bottom-up effect of abiotic factors shaping several trophic levels remains sparse. In many aquatic environments, daily changes in oxygen concentrations occur frequently. When oxygen levels drop to hypoxic levels, many fishes respond with aquatic surface respiration (ASR), during which they obtain oxygen by skimming the upper, oxygenated surface layer. By increasing time at the surface, fish become more vulnerable to fish-eating birds. We explored these cascading effects in a sulfidic spring system that harbors the endemic sulphur molly (Poecilia sulphuraria) as prey species and several fish-eating bird species. Sulfide-rich springs pose harsh conditions as hydrogen sulfide (H2S) is lethal to most metazoans and reduces dissolved oxygen (DO). Field sampling during three daytimes indicated that water temperatures rose from morning to (after)noon, resulting in the already low DO levels to decrease further, while H2S levels showed no diurnal changes. The drop in DO levels was associated with a decrease in time spent diving in sulphur mollies, which corresponded with an increase in ASR. Interestingly, the laboratory-estimated threshold at which the majority of sulphur mollies initiate ASR (ASR50: <1.7 mg/L DO) was independent of temperature and this value was exceeded daily when hypoxic stress became more severe toward noon. As fish performed ASR, large aggregations built up at the water surface over the course of the day. As a possible consequence of fish spending more time at the surface, we found high activity levels of fish-eating birds at noon and in the afternoon. Our study reveals that daily fluctuations in water’s oxygen levels have the potential to alter predator-prey interactions profoundly and thus highlights the joined actions of abiotic and biotic factors shaping the evolution of a prey species.

Communities of Soil Invertebrates near Iska-Shor Hydrogen Sulfide Springs in the Adak Nature Reserve (Komi Republic)

The results are presented of studies on soil invertebrate communities (nematodes, springtails, and large invertebrates) in shore ecosystems near hydrogen sulfide springs in the valley of the Iska-Shor stream in the Adak reserve and along river valleys at the northern boundary of the taiga zone of the Komi Republic. The taxonomic richness of the studied invertebrate groups does not change between the sampling plots. The total abundance and the abundance of individual trophic groups of springtails and large soil invertebrates decrease in plant communities near the outlet of sulfide waters, but the structure of these groups remains similar between the plots. On the contrary, the structure of nematode complexes differs between the ecosystems of the river valleys and near the hydrogen sulfide springs, where the abundance of mycotrophs increases.

Hypogenic speleogenesis, late stage epigenic overprinting and condensation-corrosion in a complex cave system in relation to landscape evolution (Toirano, Liguria, Italy)

The Toirano karst system is located in the Ligurian Alps (north Italy), around 4.5 km inland from the coastline and carved in Middle Triassic dolostone. It comprises five cave levels over a 154 m altitudinal range, specifically Ulivo (340 m a.s.l.), Colombo (247 m a.s.l.), Upper Santa Lucia (215 m a.s.l.), Lower Santa Lucia (201 m a.s.l.) and Bàsura (186 m a.s.l.) caves. The system is active at lower altitudes, as testified by the thermal spring currently located at 70 m a.s.l. along the Varatella valley. Speleogenesis was attributed to the action of epigenic processes by other authors. However, the extraordinary geodiversity of the underground morphologies and deposits are at odds with this interpretation. Accordingly, this work investigates the genesis of the Toirano karst system, in relation to the landscape evolution of the surrounding area. A detailed morphological and mineralogical investigation of cave geoforms and deposits, together with the presence of the active low thermal sulphide spring on the Varatella valley and only ~100 m below the Bàsura Cave, sustain the hypothesis of a hypogene origin of the caves. This work shows that most of the caves formed close to the former water table (base) level, in turn determined by the mean sea level. Geochronological analyses, including U/Th (n = 13) and cosmogenic burial (n = 1) dating, together with an estimated incision rate of the Varatella valley of around 0.1 mm y−1, have allowed to assess the age of the highest cave (Ulivo) at around 2.7 Ma, Colombo at ~1.8 Ma, Upper Santa Lucia at ~1.5 Ma, Lower Santa Lucia ~1.3 Ma and Bàsura at ~1.2 Ma. Estimated palaeotemperature attained through isotope analyses and fluid inclusions on speleothems suggest that the temperature of rising waters was lower than 50 °C and possibly ranging between ~12 and ~20 °C, indicating that hydrothermal fluids were not the main driver of speleogenesis, at least in the late speleogenic phases. Additionally, sulphuric acid speleogenesis by-products were not identified. Accordingly, hypogenic speleogenesis occurred because of the action of low temperature CO2-rich rising fluids. A late stage of epigenic speleogenesis has been detected because of the clear evidences of condensation-corrosion morphologies, taking place since ~150 ka (possibly earlier) when caves were finally connected to the surface because of valley enlargement. Besides uncovering the genesis of the Toirano karst system, this study demonstrates that the combination of local geology, surface vs underground geomorphological observations, climate change vs landscape evolution evaluation and geochemical data is of key importance for interpreting subsurface land-shaping processes.

Versatile cyanobacteria control the timing and extent of sulfide production in a Proterozoic analog microbial mat

Cyanobacterial mats were hotspots of biogeochemical cycling during the Precambrian. However, mechanisms that controlled O2 release by these ecosystems are poorly understood. In an analog to Proterozoic coastal ecosystems, the Frasassi sulfidic springs mats, we studied the regulation of oxygenic and sulfide-driven anoxygenic photosynthesis (OP and AP) in versatile cyanobacteria, and interactions with sulfur reducing bacteria (SRB). Using microsensors and stable isotope probing we found that dissolved organic carbon (DOC) released by OP fuels sulfide production, likely by a specialized SRB population. Increased sulfide fluxes were only stimulated after the cyanobacteria switched from AP to OP. O2 production triggered migration of large sulfur-oxidizing bacteria from the surface to underneath the cyanobacterial layer. The resultant sulfide shield tempered AP and allowed OP to occur for a longer duration over a diel cycle. The lack of cyanobacterial DOC supply to SRB during AP therefore maximized O2 export. This mechanism is unique to benthic ecosystems because transitions between metabolisms occur on the same time scale as solute transport to functionally distinct layers, with the rearrangement of the system by migration of microorganisms exaggerating the effect. Overall, cyanobacterial versatility disrupts the synergistic relationship between sulfide production and AP, and thus enhances diel O2 production.

Convergent evolution of conserved mitochondrial pathways underlies repeated adaptation to extreme environments

Extreme environments test the limits of life; yet, some organisms thrive in harsh conditions. Extremophile lineages inspire questions about how organisms can tolerate physiochemical stressors and whether the repeated colonization of extreme environments is facilitated by predictable and repeatable evolutionary innovations. We identified the mechanistic basis underlying convergent evolution of tolerance to hydrogen sulfide (H2S)-a toxicant that impairs mitochondrial function-across evolutionarily independent lineages of a fish (Poecilia mexicana, Poeciliidae) from H2S-rich springs. Using comparative biochemical and physiological analyses, we found that mitochondrial function is maintained in the presence of H2S in sulfide spring P. mexicana but not ancestral lineages from nonsulfidic habitats due to convergent adaptations in the primary toxicity target and a major detoxification enzyme. Genome-wide local ancestry analyses indicated that convergent evolution of increased H2S tolerance in different populations is likely caused by a combination of selection on standing genetic variation and de novo mutations. On a macroevolutionary scale, H2S tolerance in 10 independent lineages of sulfide spring fishes across multiple genera of Poeciliidae is correlated with the convergent modification and expression changes in genes associated with H2S toxicity and detoxification. Our results demonstrate that the modification of highly conserved physiological pathways associated with essential mitochondrial processes mediates tolerance to physiochemical stress. In addition, the same pathways, genes, and-in some instances-codons are implicated in H2S adaptation in lineages that span 40 million years of evolution.

The application of selected hydrochemical indicators in the interpretation of hydrogeochemical data – A case study from Busko-Zdrój and Solec-Zdrój (Poland)

Abstract The processes affecting the formation of the chemical composition of the waters take place in specific hydrochemical zones. The knowledge of such phenomena allows to draw conclusions regarding the origin and conditions prevailing in the regions of their occurrence, e.g. indicate a zone of active water exchange, i.e. an inflow of infiltration waters, or a zone of isolated geological structures, where diagenesis processes take place. The aim of the study was to assess the hydrochemical conditions which affect the formation of chemical composition and genesis of origin of sulfide waters from the Busko-Zdroj and Solec-Zdroj region (Poland) using selected hydrochemical indices (rNa+/rCl−, rNa+/rK+, rNa+/(rNa++rCl−), rSO42− × 100/rCl−, rCl−/rBr−, rHCO3−/rCl− and the weight index: Cl−/Br−). A detailed analysis was carried out for sulfide waters from fifteen intakes and five springs. Several aquifer systems are found in the study area. Investigated intakes and springs differ in terms of stratigraphy and lithology. The analysis of changes in the values of selected hydrochemical indices confirms that waters of the Busko-Zdroj and Solec-Zdroj region belong to two systems of circulation — “shallow” and “deep”. The formation of the chemical composition of analysed waters occurs mainly in the aquifer. The values of rNa+/rCl−, rCl−/rBr−, rNa+/(rNa++rCl−), and Cl−/Br− indices suggest that the salinity of sulfide waters may result from leaching of salt interburdens and inclusions. In the area of occurrence of sulfide springs, tectonic cracking zones enable the inflow of highly mineralized waters and thus contribute to the mixing of waters of different aquifers. High content of Cl− and Na+ ions as well as mineralization higher than in sea waters indicate the formation of waters from the upper Cretaceous level together with deposits in a sedimentary basin.