Alkaline Hot Springs Research Articles

Potential for formation of methylated thioarsenates in geothermal environments

Geothermal waters typically have elevated arsenic (As) concentrations. Various As species have been identified, including methylated thioarsenates, which present a high environmental and health risk due to high mobility and toxicity. Upon discharge from hot springs, temperature and geogenic sulfide excess decrease, while redox potential increases. The combined effects of those parameters on activities of sulfate-reducing bacteria and methanogens and thereby on extent of As methylation versus thiolation is currently unknown. Here, we incubated sediments from alkaline hot springs and outflow channels at the Tengchong geothermal region in southwestern China, where inorganic and methylated thioarsenates had been detected, at temperatures between 20 to 90 °C with different initial aqueous As and sulfur species. Results from field samples and incubation experiments showed methylated thioarsenates, but no methylated oxyarsenates, implying quantitative thiolation even at low sulfide concentrations. Enrichment cultures derived from one sediment with quantitative formation of dimethyl-dithioarsenate (DMDTA) at 55 °C, showed a dominance of inorganic trithioarsenate at 35 °C and monomethylated thioarsenates at 55 °C when incubated with two other sediments. The rate-limiting step was microbially mediated As methylation from arsenite, which was not observed at 20 °C or >= 75 °C, in contrast to thiolation of already methylated arsenates. Addition of free sulfide and thiosulfate to incubation experiments promoted formation of inorganic or monomethylated high-thiolated arsenates, while sulfate promoted full methylation and formation of DMDTA, probably due to continuous low supply of microbially produced sulfide. Since DMDTA is more mobile and toxic than inorganic and monomethylated thioarsenates, understanding constraints to its formation is especially important for future risk assessment.

Migration and controlling factors of rare earth elements in geothermal systems on the southern Tibetan Plateau

Rare earth elements (REE) serve as effective tracers of water-rock interactions, a crucial process in the evolution of geothermal systems. However, the geochemical behavior of REE during their migration within geothermal systems, particularly the fractionation mechanism, remains poorly understood. In this study, we focus on the geochemical characteristics of REE in hot springs, host rocks, and sinters from various hot spring systems in the Yadong-Gulu rift (YGR), the largest extensional rift in the southern Tibetan Plateau. The objective is to explore the factors that control REE concentrations in hot springs and elucidate the fractionation of REE during their migration. The concentrations of REE are significantly influenced by pH, Fe oxides (oxyhydroxides), and HCO3− concentrations in central and southern hot springs, whereas high reservoir temperatures contribute to higher ΣREE concentrations in northern hyperthermal springs. REE speciation calculations show that LnO2− and LnO2H are dominant complexes in northern alkaline hot springs, while carbonate complexes (LnCO3+ and Ln(CO3)2−) prevail in central and southern spring samples. Additionally, weakly acidic hot springs exhibit a prevalence of Ln3+, LnF2+, and LnSO4+ species. The chondrite-normalized REE patterns of all hot spring samples display enrichment in MREE, which is significantly distinct from the patterns observed in host rocks and sinters enriched in LREE. The fractionation of REE in the YGR hot spring systems is primarily controlled by the following processes: (1) Temperature, pH, and relative abundance of complexing agents influence the complexation of REE and further regulate their fractionation in hot springs; (2) During water-rock interaction, preferential leaching of HREE and MREE from host rocks can lead to their enrichment in alkaline hot springs. The dissolution of iron-rich sediments plays a significant role in generating the distinctive MREE bulge pattern in acid-neutral hot springs compared to host rocks; (3) The higher stability of MREE and HREE complexes in water, as well as the preferential coprecipitation of unstable LnCO3+ complexes formed by LREE with carbonates, are key factors responsible for LREE enrichment in sinters.

Polyphosphate-kinase-1 dependent polyphosphate hyperaccumulation for acclimation to nutrient loss in the cyanobacterium, Synechocystis sp. PCC 6803.

Polyphosphate is prevalent in living organisms. To obtain insights into polyphosphate synthesis and its physiological significance in cyanobacteria, we characterize sll0290, a homolog of the polyphosphate-kinase-1 gene, in the freshwater cyanobacterium Synechocystis sp. PCC 6803. The Sll0290 protein structure reveals characteristics of Ppk1. A Synechocystis sll0290 disruptant and sll0290-overexpressing Escherichia coli transformant demonstrated loss and gain of polyphosphate synthesis ability, respectively. Accordingly, sll0290 is identified as ppk1. The disruptant (Δppk1) grows normally with aeration of ordinary air (0.04% CO2), consistent with its photosynthesis comparable to the wild type level, which contrasts with a previously reported high-CO2 (5%) requirement for Δppk1 in an alkaline hot spring cyanobacterium, Synechococcus OS-B'. Synechocystis Δppk1 is defective in polyphosphate hyperaccumulation and survival competence at the stationary phase, and also under sulfur-starvation conditions, implying that sulfur limitation is one of the triggers to induce polyphosphate hyperaccumulation in stationary cells. Furthermore, Δppk1 is defective in the enhancement of total phosphorus contents under sulfur-starvation conditions, a phenomenon that is only partially explained by polyphosphate hyperaccumulation. This study therefore demonstrates that in Synechocystis, ppk1 is not essential for low-CO2 acclimation but plays a crucial role in dynamic P-metabolic regulation, including polyP hyperaccumulation, to maintain physiological fitness under sulfur-starvation conditions.

Deciphering the microbial communities of alkaline hot spring in Panamik, Ladakh, India using a high-throughput sequencing approach.

Due to their distinctive physicochemical characteristics, hot springs are extremely important. The whole genome metagenomic sequencing technology can be utilized to analyze the diverse microbial community that thrives in this habitat due to the particular selection pressure that prevails there. The current investigation emphasizes on culture-independent metagenomic study of the Panamik hot spring and its nearby areas from Ladakh, India. Based on different diversity indices, sequence analysis of the soil reservoir showed higher species richness and diversity in comparison to water and sediment samples. The mineral content and various physicochemical pameters like temperature, pH had an impact on the composition of the microbial community of the geothermal springs. The phyla Proteobacteria, Cyanobacteria, Bacteroidetes, Actinobacter, Firmicutes, and Verrucomicrobia in bacterial domain dominate the thermos-alkaline spring at Panamik in different concentrations. Economically significant microbes from the genera Actinobacter, Thermosynechoccus, Candidatus Solibacter, Chthoniobacter, Synechoccus, Pseudomonas and Sphingomonas, were prevalent in hot spring. In the archaeal domain, the most dominant phylum and genera were Euryarchaeota and Thermococcus in all the samples. Further, the most abundant species were Methanosarcina barkeri, Nitrospumilus maritimus and Methanosarcina acetivorans. The present study which only examined one of the several thermal springs present in the Himalayan geothermal area, should be regarded as a preliminary investigation of the microbiota that live in the hot springs on these remote areas. These findings suggest that further investigations should be undertaken to characterize the ecosystems of the Panamik hot spring, which serve as a repository for unidentified microbial lineages.

Draft genome of Chloroflexus sp. MS-CIW-1, of the Chloroflexus sp. MS-G group from Mushroom Spring, Yellowstone National Park.

Chloroflexus sp. MS-CIW-1 was isolated from a phototrophic mat in Mushroom Spring, an alkaline hot spring in Yellowstone National Park, WY, USA. We report the draft genome of 4.8 Mb consisting of 6 contigs with 3755 protein-coding genes and a GC content of 54.45%.

Towards understanding formation of polytungstates in tungsten-bearing hot springs and its environmental implications

Polytungstates have toxicity, mobility, and bioavailability quite different from those of monomeric tungstates, the most common tungsten (W) species. To date, relevant studies of polytungstates have been conducted under laboratory conditions, and there is a lack of studies on such W species in natural waters. In the present study, polytungstates at environmentally relevant concentrations were detected in a number of investigated hot springs. All the hot springs with high polytungstates concentrations (> 10 μg/L) have vent temperatures above 70 °C and pH values above 8, and polytungstates are immeasurable in all the acidic hot springs. Further inspection showed that the detected polytungstates were not isopolytungstates but likely heteropolytungstates forming via incorporation of silicate or borate enriched in the hot springs into tungstates at elevated temperatures. These detectable polytungstates, however, might also be polymeric thiotungstates in view of their close correlation with aqueous sulfide and thiotungstates and their specific retention time during the chromatographic separation. More precise identification of the polytungstates depends on improvement of the used analytical technique to achieve a further chromatographic separation of different kinds of polytungstates. Upon the discharge of the hot springs, the aqueous W was transported to the hot spring sediments due to its adsorption onto the Fe-bearing minerals there. Although the pH values of the hot springs were the critical parameter for the W adsorption, the substantial formation of polytungstates in some neutral to alkaline hot springs could inhibit the adsorption to some degree, thereby contributing somewhat to the enrichment of W in such springs. This is the first study reporting polytungstates and their environmental behavior in natural hot springs. It is possible that polytungstates are widely present in high-temperature, neutral to alkaline hot springs hydrochemically similar to those involved in this study.

An approach combining chlorine isotopes and hydrochemistry for identification of magmatic fluid-affected hydrothermal systems

Identification of hydrothermal systems affected by magmatic fluid input is relevant for geothermal energy development. Thus, an approach for identifying such systems based on chlorine isotope composition and auxiliary hydrochemical indices was proposed. The approach enabled us to distinguish Rehai, a magmatic hydrothermal area in the Tengchong volcanic region of China, from several other typical non-magmatic hydrothermal areas in Tengchong: Menglian, Shiqiang, and Jietou. The hot springs in the non-Rehai areas featured high δ37Cl values, reflecting an exclusive contribution of chlorine from hostrock leaching. By contrast, some hot springs with much lower δ37Cl values occurred in Rehai, all of which were nearly fully equilibrated waters with respect to reservoir hostrocks, rich in chloride and bromide. These springs should have the closest relationship with the fluids released from the underlying magma chamber. Notably, the potential reservoir processes that geothermal waters may undergo after receiving an input of magmatic fluids can further alter their chlorine isotope compositions to various degrees. Therefore, a deep understanding of these processes would help improve the use of the proposed approach based primarily on chlorine isotopes. Regarding Rehai, all the neutral to alkaline hot springs with δ37Cl values ranging from −0.44 ‰ to 0.31 ‰ evolved from a parent geothermal fluid that received an input of magmatic fluids—via adiabatic cooling, conductive cooling, mixing with low-temperature shallow groundwaters, or a combination of some of these processes. By contrast, the acidic Rehai hot springs with the highest δ37Cl values (up to 1.12 ‰) were essentially locally perched groundwaters heated by geothermal steam separated from underlying geothermal fluids upon their adiabatic cooling; thus, they were much less to do with the parent geothermal fluid than the neutral to alkaline springs were. Hence, only the neutral to alkaline Rehai hot springs not strongly affected by the mixing of shallow groundwaters and adiabatic cooling can reflect the chlorine isotope characteristics of intrusive magmatic fluids. Overall, chlorine isotope composition in combination with hydrochemistry has proven to be a robust tool for identifying a magmatic fluid-affected hydrothermal system.

Effects of Mineral on Taxonomic and Functional Structures of Microbial Community in Tengchong Hot Springs via in-situ cultivation

Diverse mineralogical compositions occur in hot spring sediments, but the impact of minerals on the diversity and structure of microbial communities remains poorly elucidated. In this study, different mineral particles with various chemistries (i.e., hematite, biotite, K-feldspar, quartz, muscovite, aragonite, serpentine, olivine, barite, apatite, and pyrite) were incubated for ten days in two Tengchong hot springs, one alkaline (pH ~ 8.34) with a high temperature (~ 82.8 °C) (Gumingquan, short as GMQ) and one acidic (pH ~ 3.63) with a relatively low temperature (~ 43.3 °C) (Wenguangting, short as WGT), to determine the impacts of minerals on the microbial communities taxonomic and functional diversities. Results showed that the mineral-associated bacterial taxa differed from those of the bulk sediment samples in the two hot springs. The relative abundance of Proteobacteria, Euryarchaeota, and Acidobacteria increased in all minerals, indicating that these microorganisms are apt to colonize on solid surfaces. The α-diversity indices of the microbial communities on the mineral surfaces in the WGT were higher than those from the bulk sediment samples (p < 0.05), which may be caused by the stochastically adhering process on the mineral surface during 10-day incubation, different from the microbial community in sediment which has experienced long-term environmental and ecological screening. Chemoheterotrophy increased with minerals incubation, which was high in most cultured minerals (the relative contents were 5.8 − 21.4%). Most notably, the sulfate respiration bacteria (mainly related to Desulfobulbaceae and Syntrophaceae) associated with aragonite in the acidic hot spring significantly differed from other minerals, possibly due to the pH buffering effect of aragonite providing more favorable conditions for their survival and proliferation. By comparison, aragonite cultured in the alkaline hot spring highly enriched denitrifying bacteria and may have promoted the nitrogen cycle within the system. Collectively, we speculated that diverse microbes stochastically adhered on the surface of minerals in the water flows, and the physicochemical properties of minerals drove the enrichment of certain microbial communities and functional groups during the short-term incubation. Taken together, these findings thereby provide novel insights into mechanisms of community assembly and element cycling in the terrestrial hydrothermal system associated with hot springs.

Different sulfide to arsenic ratios driving arsenic speciation and microbial community interactions in two alkaline hot springs

Arsenic (As) is ubiquitous in geothermal fluids, which threatens both water supply safety and local ecology. The co-occurrence of sulfur (S) and As increases the complexity of As migration and transformation in hot springs. Microorganisms play important roles in As–S transformation processes. In the present study, two Tibetan alkaline hot springs (designated Gulu [GL] and Daba [DB]) with different total As concentrations (0.88 mg/L and 12.42 mg/L, respectively) and different sulfide/As ratios (3.97 and 0.008, respectively) were selected for investigating interactions between As–S geochemistry and microbial communities along the outflow channels. The results showed that As–S transformation processes were similar, although concentrations and percentages of As and S species differed between the two hot springs. Thioarsenates were detected at the vents of the hot springs (18% and 0.32%, respectively), and were desulfurized to arsenite along the drainage channel. Arsenite was finally oxidized to arsenate (532 μg/L and 12,700 μg/L, respectively). Monothioarsenate, total As, and sulfate were the key factors shaping the changes in microbial communities with geochemical gradients. The relative abundances of sulfur reduction genes (dsrAB) and arsenate reduction genes (arsC) were higher in upstream portions of GL explaining high thiolation. Arsenite oxidation genes (aoxAB) were relatively abundant in downstream parts of GL and at the vent of DB explaining low thiolation. Sulfur oxidation genes (soxABXYZ) were abundant in GL and DB. Putative sulfate-reducing bacteria (SRB), such as Desulfuromusa and Clostridium, might be involved in forming thioarsenates by producing reduced S for chemical reactions with arsenite. Sulfur-oxidizing bacteria (SOB), such as Elioraea, Pseudoxanthomonas and Pseudomonas, and arsenite-oxidizing bacteria (AsOB) such as Thermus, Sulfurihydrogenibium and Hydrogenophaga, may be responsible for the oxidation of As-bound S, thereby desulfurizing thioarsenates, forming arsenite and, by further abiotic or microbial oxidation, arsenate. This study improves our understanding of As and S biogeochemistry in hot springs.

Microorganisms of Microbial Mats from an Alkaline Hot Spring of Baikal Rift Zone as Bioagents in a Biofuel Cell

The microbial diversity, transformation potential and ability of microorganisms of the microbial mat consortium of the Kucheger thermal spring (Baikal Rift Zone) to generate electricity were studied. High-throughput sequencing showed the predominance of representatives of the Proteobacteria phylum in the microbial mat community (85.5% of the number of classified bacterial sequences). Among Proteobacteria, filamentous sulfur bacteria of the genus Thiothrix are the most numerous (66.1%). In addition, bacteria of the families Rhodocyclaceae (3%) and Comamonadaceae (7.3%) were present in the mat community. The Bacteroidetes phylum was represented by sequences belonging mainly to the Flavobacteriaceae family (6.8%). The sequences of other phyla accounted for no more than 0.5% of the total number of classified sequences. A wide metabolic activity of microorganisms of mat Kucheger-15 was revealed. The high electrogenic ability of microorganisms of the consortium of microbial mats Kucheger-15 in biofuel cells (BFCs) is shown. Mat-based BFCs generated electricity by adding substrates such as peptone, cellulose, starch. Peptone, glucose, tween-80, starch, sodium acetate, and cellulose were used as substrates. Peptone turned out to be the most effective substrate for the production of electricity in BFCs based on Kucheger microbial mat microorganisms. The addition of a mixture of these substrates to the anolyte (the concentration of each of them is 2.5 g/l) made it possible to achieve some increase in energy release (especially the output current) compared to BFC based on each of these substrates separately. The presence of a wide variety of different microorganisms with broad substrate specificity, the ability to function under extreme conditions (high temperature, high pH values), their well-coordinated work and adaptation to each other and to the resulting metabolites, and stability over time allow us to speak of high prospects for the use of hot spring mats in BFC technologies.

Metagenomes and Metagenome-Assembled Genomes from Substrate-Amended Hot Spring Sediment Incubations from Yellowstone National Park.

ABSTRACTHere, we report on eight sediment metagenomes obtained from an alkaline hot spring, with their corresponding metagenome-assembled genomes. Samples had been incubated for 48 h with various substrate amendments in conjunction with the amino acid analog l-homopropargylglycine in a study targeted at identifying anabolicly active uncultured thermophilic archaea and bacteria.

Hot spring bathing accelerates wound healing and enhances heat retention effect in guinea pigs.

This study aimed to demonstrate the effects of hot springs on wound healing and heat retention by performing comparative experiments with tap water. The hot spring water used in this study was from an alkaline hot spring that was rich in sodium and chloride ions and exhibited high reducibility. Guinea pigs were divided into a hot spring bathing group and a tap water bathing group, and a bathing test was conducted for eight consecutive days. A comparison of the plasma amino acid composition between the two groups after the bathing test revealed differences in the concentrations of several amino acids associated with wound healing. Image analysis demonstrated that wounds made on the abdominal skin of guinea pigs were significantly contracted by hot spring bathing compared to that by tap water bathing, and histopathological findings showed that wound healing was accelerated. In the thermography test, changes in body surface temperature after bathing were investigated in both groups. The heat retention effect was not observed in the tap water bathing group after bathing, whereas it was enhanced in the hot spring bathing group until 30 min after bathing. In conclusion, this study demonstrated that hot spring bathing accelerates wound healing and has a more significant heat retention effect than tap water bathing.

Comfortable and dermatological effects of hot spring bathing provide demonstrative insight into improvement in the rough skin of Capybaras

The purpose of this study was to clarify dermatologically the favorable effects of hot spring bathing on the rough skin in Capybaras. Non-volcanic hot springs used in this study showed alkaline quality of water (pH 9.3), containing sodium and chloride ions. The normal skin in Capybaras was characterized by the presence of relatively thick epidermis with mild alkaline state (pH 8.26). The dorsal skin had melanin granules in the basal layer. Their rough skin affected in the Japanese cold winter was improved by daily bathing in an alkaline hot spring. The skin properties returned to the normal skin conditions (moisture, melanin and erythema values) observed in the summer. The facial expression mainly changes in the eyes was scored to evaluate comfortable status. The comfortable status during hot spring bathing significantly increased as compared with that observed before bathing (p < 0.01). The thermography revealed a heat retention effect of body temperature after hot spring bathing for 30 min. In conclusion, this study demonstrates that hot spring had significantly comfortable and dermatological effects on the basis of evaluation for the skin and body conditions in Capybaras.

Taxonomical and functional diversity of microbial communities in two hot springs of the Baikal rift zone

The Baikal Rift Zone hosts many hot springs with a wide range of temperature and physical-chemical conditions, which may harbour different niches for the distribution of microbial communities. We investigated microbial community composition and their functional activity in two alkaline hot springs with a temperature range of 34.4 to 73.6°C. Comparative analysis of the composition of the dominant taxa showed significant differences depending on the collection sites. In the community of high-temperature zones with a water temperature of 55-64°C, a high proportion of thermophilic bacteria Acetothermia (up to 57.9%), Deinococcus-Thermus (up to 50%), and Aquificae (up to 10.8%). Proteobacteria (29-77%) and Firmicutes (15-26%) dominate in the sulphide-free Garga spring (73-75°C). The functional analysis of the microbial community showed that the primary producers are cyanobacteria, anoxygenic phototrophs, and chemolithotrophic bacteria. At the terminal stages of the mineralization of organic matter, sulphate-reducing bacteria are the main destructors in the microbial communities in hot springs. The cyano-bacterial and sulfidogenic microbial communities play an important role in the formation of geochemical barriers and mineral formation.

Competition of equilibrium and kinetic silicon isotope fractionation during silica precipitation from acidic to alkaline pH solutions in geothermal systems

As an important volcanic geothermal region in China, Tengchong belongs to the Mediterranean-Himalayan geothermal belt and is characterized by a wide distribution of geothermal systems. The study area- Rehai- is the sole geothermal area in Tengchong in mainland China that discharges both acidic and alkaline hot springs with pH values ranging from 1.6 to 9.7 at temperatures between 50 and 97 °C. Natural geothermal environments with large variations in pH and temperature are ideal study sites to investigate silicon (Si) isotope fractionation mechanisms which are still insufficiently understood. In this study, we investigated 3 different geothermal systems, which have distinct fluid characteristics: (1) type I fluid from Diretiyan Spring (pH: 1.6–2.5, HSO4 water, saturated with respect to quartz), (2) type II fluid from Zhenzhuquan Spring (pH: 6.4, NaClSO4 water, saturated with respect to quartz), and (3) type III fluid from Dagunguo Spring (pH: 7.8–9.7, NaCl water, oversaturated with respect to amorphous silica: SiO2am). The mechanisms controlling Si isotope fractionation during Si precipitation differ significantly between the three fluid types. In type I fluid, equilibrium fractionation controls Si isotope variability during silica precipitation, causing the highest natural Si isotope equilibrium fractionation (Δ30Si) detected to date, ranging in Δ30Siquartz-fluid from +1.09‰ to +2.78‰. The equilibrium isotope fractionation is essentially caused by balanced precipitation and dissolution rates and high ionic strength of the geothermal fluids. In type II fluid, amorphous silica formed during evaporation and/or cooling of the spring water during capillary rise and a kinetically controlled, uni-directional Si isotope fractionation is observed. In type III fluid, the Δ30SiSiO2am-fluid ranges from −1.57‰ to +0.55‰ at the temperature range of 80–100 °C. The Δ30SiSiO2am-fluid show a shift from kinetic to equilibrium controlled fractionation and demonstrate that isotopic re-equilibration can reset the original kinetic Si isotope values in dependence of the hydrochemical conditions like pH, temperature and ionic strength as well as reaction time. Here we show that isotopic re-equilibration after solid formation can shift the isotopic signatures originally inherited during precipitation, challenging the interpretation of Si isotope values in the ancient rock record.

Comparative Metagenomic Analysis of Two Alkaline Hot Springs of Madhya Pradesh, India and Deciphering the Extremophiles for Industrial Enzymes.

Hot springs are considered to be a unique environment with extremophiles, that are sources of industrially important enzymes, and other biotechnological products. The objective of this study was to undertake, analyze, and characterize the microbiome of two major hot springs located in the state of Madhya Pradesh explicitly, Chhoti Anhoni (Hotspring 1), and Badi Anhoni (Hotspring 2) to find out the inhabitant microbial population, and their functional characteristics. The taxonomic analysis of the microbiome of the hot springs revealed the phylum Proteobacteria was the most abundant taxa in both the hot-springs, however, its abundance in hot-spring 1 (~88%) was more than the hot-spring 2 (~52%). The phylum Bacteroides (~10–22%) was found to be the second most abundant group in the hot-springs followed by Spirocheates (~2–11%), Firmicutes (~6–8%), Chloroflexi (1–5%), etc. The functional analysis of the microbiome revealed different features related to several functions including metabolism of organics and degradation of xenobiotic compounds. The functional analysis showed that most of the attributes of the microbiome was related to metabolism, followed by cellular processes and environmental information processing functions. The functional annotation of the microbiomes at KEGG level 3 annotated the sequences into 279 active features that showed variation in abundance between the hot spring samples, where hot-spring 1 was functionally more diverse. Interestingly, the abundance of functional genes from methanogenic bacteria, was higher in the hot-spring 2, which may be related to the relatively higher pH and temperature than Hotspring 1. The study showed the presence of different unassigned bacterial taxa with high abundance which indicates the potential of novel genera or phylotypes. Culturable isolates (28) were bio-prospected for industrially important enzymes including amylase, protease, lipase, gelatinase, pectinase, cellulase, lecithinase, and xylanase. Seven isolates (25%) had shown positive results for all the enzyme activities whereas 23 isolates (82%) produced Protease, 27 isolates (96%) produced lipase, 27 isolates produced amylase, 26 isolates (92%) produced cellulase, 19 isolates (67%) produced pectinase, 19 isolates (67%) could produce lecithinase, and 13 isolates (46%) produced gelatinase. The seven isolates, positive for all the enzymes were analyzed further for quantitative analysis and identified through molecular characterization.

Hydrogeochemical Constraints Shape Hot Spring Microbial Community Compositions: Evidence From Acidic, Moderate‐Temperature Springs and Alkaline, High‐Temperature Springs, Southwestern Yunnan Geothermal Areas, China

AbstractEnvironmental factors (e.g., temperature and pH) shaping the distribution of microbial communities in hot springs have been extensively studied, whereas how hydrochemical formation mechanisms and hydrological circulation processes affect microbial community composition is not comprehensively elucidated. In the present study, hydrochemical, isotopic, and high‐throughput sequencing methods were employed to investigate hydrochemical characteristics and evolution of springwater as well as their underlying roles in shaping the microbial community in multiple acidic and alkaline hot springs in southwestern Yunnan, China. Distinct hydrochemical (e.g., pH, temperature, sulfate, SiO2, and trace metals) and isotopic (δ2H and δ18O) characteristics revealed the recharge sources and circulation processes of springwater were different in alkaline, high‐temperature and acidic, moderate‐temperature hot springs. Two acidic, moderate‐temperature springs (43°C–55°C), characterized by high sulfate, showed shallow circulation depths and were potentially heated by upwelling hot, high H2S abundance gases, and sulfur oxidation might be one of the main underlying hydrochemical processes. Seven alkaline, high‐temperature springs (&gt;70°C), in contrast, which originated from a different recharge source as indicated by the lighter isotopic compositions (δ2H and δ18O), showed characteristics of deeper circulation. Hydrogenobacter sp. is the most abundant microorganism in alkaline, high‐temperature springs, whereas acidic, moderate‐temperature springs are mainly composed of Chlorobiaceae, Thiomonas sp., Halothiobacillus sp., Sulfurihydrogenibium sp., and Hydrogenobaculum sp. which have been reported to possess the potentials to cycle sulfur. The hydrochemical constraints on shaping microbial communities may help us better understand biogeochemical cycles across a range of temperatures in acidic and alkaline springs.

Genomic Insights of "Candidatus Nitrosocaldaceae" Based on Nine New Metagenome-Assembled Genomes, Including "Candidatus Nitrosothermus" Gen Nov. and Two New Species of "Candidatus Nitrosocaldus".

“Candidatus Nitrosocaldaceae” are globally distributed in neutral or slightly alkaline hot springs and geothermally heated soils. Despite their essential role in the nitrogen cycle in high-temperature ecosystems, they remain poorly understood because they have never been isolated in pure culture, and very few genomes are available. In the present study, a metagenomics approach was employed to obtain “Ca. Nitrosocaldaceae” metagenomic-assembled genomes (MAGs) from hot spring samples collected from India and China. Phylogenomic analysis placed these MAGs within “Ca. Nitrosocaldaceae.” Average nucleotide identity and average amino acid identity analysis suggested the new MAGs represent two novel species of “Candidatus Nitrosocaldus” and a novel genus, herein proposed as “Candidatus Nitrosothermus.” Key genes responsible for chemolithotrophic ammonia oxidation and a thaumarchaeal 3HP/4HB cycle were detected in all MAGs. Furthermore, genes coding for urea degradation were only present in “Ca. Nitrosocaldus,” while biosynthesis of the vitamins, biotin, cobalamin, and riboflavin were detected in almost all MAGs. Comparison of “Ca. Nitrosocaldales/Nitrosocaldaceae” with other AOA revealed 526 specific orthogroups. This included genes related to thermal adaptation (cyclic 2,3-diphosphoglycerate, and S-adenosylmethionine decarboxylase), indicating their importance for life at high temperature. In addition, these MAGs acquired genes from members from archaea (Crenarchaeota) and bacteria (Firmicutes), mainly involved in metabolism and stress responses, which might play a role to allow this group to adapt to thermal habitats.

The role of hydrothermal fluids in sedimentation in saline alkaline lakes: Evidence from Nasikie Engida, Kenya Rift Valley

AbstractSaline alkaline lakes that precipitate sodium carbonate evaporites are most common in volcanic terrains in semi‐arid environments. Processes that lead to trona precipitation are poorly understood compared to those in sulphate‐dominated and chloride‐dominated lake brines. Nasikie Engida (Little Magadi) in the southern Kenya Rift shows the initial stages of soda evaporite formation. This small shallow (&lt;2 m deep; 7 km long) lake is recharged by alkaline hot springs and seasonal runoff but unlike neighbouring Lake Magadi is perennial. This study aims to understand modern sedimentary and geochemical processes in Nasikie Engida and to assess the importance of geothermal fluids in evaporite formation. Perennial hot‐spring inflow waters along the northern shoreline evaporate and become saturated with respect to nahcolite and trona, which precipitate in the southern part of the lake, up to 6 km from the hot springs. Nahcolite (NaHCO3) forms bladed crystals that nucleate on the lake floor. Trona (Na2CO3·NaHCO3·2H2O) precipitates from more concentrated brines as rafts and as bottom‐nucleated shrubs of acicular crystals that coalesce laterally to form bedded trona. Many processes modify the fluid composition as it evolves. Silica is removed as gels and by early diagenetic reactions and diatoms. Sulphate is depleted by bacterial reduction. Potassium and chloride, of moderate concentration, remain conservative in the brine. Clastic sedimentation is relatively minor because of the predominant hydrothermal inflow. Nahcolite precipitates when and where pCO2 is high, notably near sublacustrine spring discharge. Results from Nasikie Engida show that hot spring discharge has maintained the lake for at least 2 kyr, and that the evaporite formation is strongly influenced by local discharge of carbon dioxide. Brine evolution and evaporite deposition at Nasikie Engida help to explain conditions under which ancient sodium carbonate evaporites formed, including those in other East African rift basins, the Eocene Green River Formation (western USA), and elsewhere.

A micrometer-scale snapshot on phototroph spatial distributions: mass spectrometry imaging of microbial mats in Octopus Spring, Yellowstone National Park.

Microbial mats from alkaline hot springs in the Yellowstone National Park are ideal natural laboratories to study photosynthetic life under extreme conditions, as well as the nuanced interactions of oxygenic and anoxygenic phototrophs. They represent distinctive examples of chlorophototroph (i.e., chlorophyll or bacteriochlorophyll-based phototroph) diversity, and several novel phototrophs have been first described in these systems, all confined in space, coexisting and competing for niches defined by parameters such as light, oxygen, or temperature. In a novel approach, we employed mass spectrometry imaging of chloropigments, quinones, and intact polar lipids (IPLs) to describe the spatial distribution of different groups of chlorophototrophs along the~1cm thick microbial mat at 75µm resolution and in the top~1.5mm green part of the mat at 25µm resolution. We observed a fine-tuned sequence of oxygenic and anoxygenic chlorophototrophs with distinctive biomarker signatures populating the microbial mat. The transition of oxic to anoxic conditions is characterized by an accumulation of biomarkers indicative of anoxygenic phototrophy. It is also identified as a clear boundary for different species and ecotypes, which adjust their biomarker inventory, particularly the interplay of quinones and chloropigments, to prevailing conditions. Colocalization of the different biomarker groups led to the identification of characteristic IPL signatures and indicates that glycosidic diether glycerolipids are diagnostic for anoxygenic phototrophs in this mat system. The zoom-in into the upper green part further reveals how oxygenic and anoxygenic phototrophs share this microenvironment and informs on subtle, microscale adjustments in lipid composition of Synechococcus spp.