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A few members of the bacterial genus Thermus have been shown to be incomplete denitrifiers, terminating with nitrite (NO2−) or nitrous oxide (N2O). However, the denitrification abilities of the genus as a whole remain poorly characterized. Here, we describe diverse denitrification phenotypes and genotypes of a collection of 24 strains representing ten species, all isolated from a variety of geothermal systems in China. Confirmed terminal products of nitrate reduction were nitrite or N2O, while nitric oxide (NO) was inferred as the terminal product in some strains. Most strains produced N2O; complete denitrification was not observed. Denitrification phenotypes were largely consistent with the presence of denitrification genes, and strains of the same species often had the same denitrification phenotypes and largely syntenous denitrification gene clusters. Genes for nirS and nirK coexisted in three Thermus brockianus and three Thermus oshimai genomes, which is a unique hallmark of some denitrifying Thermus strains and may be ecologically important. These results show that incomplete denitrification phenotypes are prominent, but variable, within and between Thermus species. The incomplete denitrification phenotypes described here suggest Thermus species may play important roles in consortial denitrification in high-temperature terrestrial biotopes where sufficient supply of oxidized inorganic nitrogen exists.

In recent years, scientists have increasingly focused on the microbial diversity of high-altitude hot springs to explore the biotechnological applications of extremophiles. In this regard, a total of 107 thermophilic bacilli were isolated from 9 high-altitude mineralized geothermal springs (of temperatures ranging from 27.5 to 70 °C) located within the territory of Armenia and Nagorno-Karabakh. The isolated bacilli were phylogenetically profiled and studied for their potential to produce extracellular hydrolytic enzymes (protease, amylase, and lipase). The identification of isolates based on 16S rRNA gene sequences revealed their relationship to members of more than 22 distinct species, of 8 different genera, namely Aeribacillus, Anoxybacillus, Bacillus, Brevibacillus, Geobacillus, Parageobacillus, Paenibacillus and Ureibacillus. Bacillus licheniformis, Parageobacillus toebii and Anoxybacillus flavithermus were found to be the most abundant species in the springs that were studied. Some of the isolated bacilli shared less than 91–97% sequence identity with their closest match in GenBank, indicating that Armenian geothermal springs harbor novel bacilli, at least at the species level. 71% of the isolates actively produced at least one or more extracellular proteases, amylases, or lipases. In total, 22 strains (28.6%) were efficient producers of all three types of thermostable enzymes.

Geothermal springs are some of the most obvious indicators of the existence of high-temperature geothermal resources in the subsurface. However, geothermal springs can also occur in areas of low average subsurface temperatures, which makes it difficult to assess exploitable zones. To address this problem, this study quantitatively analyzes the conditions associated with the formation of geothermal springs in fault zones, and numerically investigates the implications that outflow temperature and discharge rate from geothermal springs have on the geothermal background in the subsurface. It is concluded that the temperature of geothermal springs in fault zones is mainly controlled by the recharge rate from the country rock and the hydraulic conductivity in the fault damage zone. Importantly, the topography of the fault trace on the land surface plays an important role in determining the thermal temperature. In fault zones with a permeability higher than 1 mD and a lateral recharge rate from the country rock higher than 1 m3/day, convection plays a dominant role in the heat transport rather than thermal conduction. The geothermal springs do not necessarily occur in the place having an abnormal geothermal background (with the temperature at certain depth exceeding the temperature inferred by the global average continental geothermal gradient of 30 °C/km). Assuming a constant temperature (90 °C here, to represent a normal geothermal background in the subsurface at a depth of 3,000 m), the conditions required for the occurrence of geothermal springs were quantitatively determined.

The growing demand for efficient sustainable biocatalysts for industrial applications has driven the exploration of extremozymes from extremophiles, particularly those thriving in geothermal environments. This study aimed to isolate and characterize extracellular amylase-producing thermophilic bacteria from the Nelumwewa geothermal spring in Sri Lanka, an underexplored ecosystem. Among the isolated thermophilic bacterial strains, NW2 isolates exhibited a prominent extracellular amylase activity. Molecular characterization by 16S rRNA gene sequencing confirmed the close phylogenetic relationship between NW2 and Thermaerobacillus caldiproteolyticus, which is well-known for thermostable proteases. Biochemical assays revealed optimal amylase activity of NW2 isolate at 60 °C and pH 8.0, with a crude enzyme activity of 0.85 U/mL. The enzyme demonstrated efficient hydrolysis of raw cassava starch, highlighting its potential for industrial applications in food, biofuel, and detergent industries. This study reports the first T. caldiproteolyticus-like strain from Sri Lanka with significant extracellular amylase activity, emphasizing the biotechnological potential of geothermal springs as sources of novel extremozymes. These findings contribute to the growing repository of thermostable enzymes, highlighting the need for further exploration of Sri Lanka’s geothermal microbial diversity for industrial biocatalysts.

Geothermal waters are extensively useful for various purposes such as societal benefits, irrigation, industrial and domestic consumptions. However, its physicochemical characterization is very important before using it for any rationale. The main objective of this paper is to identify the hydrochemistry of geothermal water which is placed in the southern part of Gujarat such as Unai hot springs and Saputara geothermal springs, and West Coast Geothermal Province (WCGP) like the Tural-Rajwadi group of hot springs. The standard methods were used to carry out the analysis of geothermal water. Piper, Stiff, Gibbs, Ternary, Schoeller, Extended Durov, Wilcox, and Spatial distribution diagrams were plotted to categorize water samples in facies. The geochemistry of groundwater is influenced by the presence of most important ions such as Na + , Ca 2+ , Mg 2+ , K + , Cl − , HCO 3 − , and SO 4 2− . Weathering of some rocks leads to the deposition of these ions in water. The geothermal spring of Unai contains a high TDS concentration of around 1000 mg/l thus it cannot be used for drinking purposes, but it can be utilized for domestic, balneology, and industrial purposes. However, after desalination, this water can be utilized for drinking purposes. In Tural-Rajwadi hot springs, TDS concentration was > 900 mg/l and pH varies from 7 to 8, hence it can be used for domestic and industrial purposes. The temperature range of the Tural-Rajwadi geothermal hot spring is 55–65 °C which is very useful for milk pasteurization, industrial operations, balneology facilities like greenhouses and aquaculture ponds, and domestic purposes.

Hydrogen peroxide (H2O2), superoxide (O2•-), and hydroxyl radicals (OH•) are produced in natural waters via ultraviolet (UV) light-induced reactions between dissolved oxygen (O2) and organic carbon, and further reaction of H2O2 and Fe(II) (i.e., Fenton chemistry). The temporal and spatial dynamics of H2O2 and other dissolved compounds (Fe(II), Fe(III), H2S, O2) were measured during a diel cycle (dark/light) in surface waters of three acidic geothermal springs (Beowulf Spring, One Hundred Springs Plain, and Echinus Geyser Spring; pH = 3-3.5, T = 68-80 °C) in Norris Geyser Basin, Yellowstone National Park. In situ analyses showed that H2O2 concentrations were lowest (ca. 1 μM) in geothermal source waters containing high dissolved sulfide (and where oxygen was below detection) and increased by two-fold (ca. 2-3 μM) in oxygenated waters corresponding to Fe(III)-oxide mat formation down the water channel. Small increases in dissolved oxygen and H2O2 were observed during peak photon flux, but not consistently across all springs sampled. Iron-oxide microbial mats were sampled for molecular analysis of ROS gene expression in two primary autotrophs of acidic Fe(III)-oxide mat ecosystems: Metallosphaera yellowstonensis (Archaea) and Hydrogenobaculum sp. (Bacteria). Expression (RT-qPCR) assays of specific stress-response genes (e.g., superoxide dismutase, peroxidases) of the primary autotrophs were used to evaluate possible changes in transcription across temporal, spatial and/or seasonal samples. Data presented here documented the presence of H2O2 and general correlation with dissolved oxygen. Moreover, two dominant microbial populations expressed ROS response genes throughout the day, but showed less expression of key genes during peak sunlight. Oxidative stress response genes (especially external peroxidases) were highly-expressed in microorganisms within Fe(III)-oxide mat communities, suggesting a significant role for these proteins during survival and growth in situ.

Geothermal resources, as a renewable and clean source of energy, are attracting widespread attention globally. In China, most medium to high enthalpy geothermal resources are developed in the Tibetan Plateau, especially in the rift zone of Southern Tibet. To further investigate the genesis mechanisms of geothermal resources, this study collected geothermal spring samples from the Cuona-Woka rift zone in Southern Tibet. Hydrochemical and isotopic characteristics were analyzed to reveal the origin, evolution, reservoir temperature, and circulation mechanisms of the geothermal waters. The exposed temperature of the geothermal spring ranges from 34 to 67 °C. Compared with HCO 3 -Ca·Na and HCO 3 -Na type samples, HCO 3 ·Cl-Na and HCO 3 ·SO 4 -Na type samples have higher concentrations of Cl − and trace elements. The geothermal springs are recharged by a mixture of meteoric water, snow-melt water, and magmatic water. The recharge areas had an elevation range from 5091 to 6087 m, with temperatures from −5 to −10 °C. The hydrochemical processes are dominated by silicate and carbonate dissolution, and positive cation exchange, with local gypsum dissolution. Solute geothermometers, silica-enthalpy mixing models, and geothermal conceptual model indicate that there exist shallow geothermal reservoirs (temperature = 137–162 °C) mixed by surficial cold groundwater and initial deep geothermal reservoirs (temperature = 196–212 °C), respectively. Finally, two genesis models of geothermal waters are proposed: the deep melt mixing and heating model (Type A) and the high-temperature steam heating model (Type B). The achievements of this study would provide valuable insight into geothermal research and exploitation in the Tibetan Plateau.

During the ongoing uplift and expansion of the southeastern margin of the Tibetan Plateau, the front edge of the Sichuan‐Yunnan rhombic block (SYB) has experienced intense tectonic activity and frequent seismicity. In this study, the fluid geochemistry in the primary active faults at the front edge of the SYB was investigated, with the aim of understanding the tectonic activity and intersection relationship between the Xiaojiang fault (XJF) and the Red River fault (RRF). Thermal spring water and gases exhibit a coupled spatial distribution relationship; relatively high ion concentrations and 3He/4He ratios (Rc/Ra ratios of 0.21 to 0.62Ra) are observed along the RRF, Qujiang fault (QJF), and Shiping‐Jianshui fault (SJF). Multidisciplinary research results have indicated that mantle‐derived intrusion has been detected in the crust beneath the QJF and SJF. The current tectonic activity in the front edge of the SYB remains intense, with compressive stresses shifting toward the western side of the XJF and accumulating on the QJF and SJF. This has led to the development of fractures, enhancing the water–rock interaction and deep‐derived gas degassing along the faults. The unmixing characteristics of fluids at the intersection area of these two faults suggest the absence of conduits for fluid migration between the faults. Owing to the lower gas 3He/4He ratios, lower shear strain rates, stable reservoir temperature field, and extremely low historical seismicity in the Indo‐Chinese block, it is speculated that the current movement of the XJF may not cut through the RRF and continue southward. Plain Language Summary Fluids serve as carriers of information regarding deep activities, and are known to migrate along active faults. Additionally, fluid geochemistry is highly sensitive to tectonic activity. Given the intense tectonic activity and frequent seismicity experienced at the front edge of the Sichuan‐Yunnan rhombic block (SYB), our study focuses on investigating the fluid geochemical characteristics of the primary active faults in this region. Significant spatial differences in fluid chemistry are observed, particularly with respect to relatively high ion concentrations and mantle He values along the Red River fault (RRF), Qujiang fault (QJF), and Shiping‐Jianshui fault (SJF). Furthermore, the lack of conduits facilitating fluid migration between the Xiaojiang (XJF) and RRF is evident from the distinct unmixed characteristics of the fluids. Multidisciplinary results indicate the presence of mantle‐derived intrusion into the crust beneath the QJF and SJF. The compressive stresses have shifted toward the western side of the XJF and are accumulated on the QJF and SJF, resulting in the observed spatial variations in fluid geochemistry. Ultimately, these spatial differences can be attributed to the unique intersection relationship between the XJF and RRF. Key Points Mantle‐derived intrusion has been detected in the crust beneath the Qujiang fault (QJF) and Shiping‐Jianshui fault (SJF) Tectonics remains active at the front edge of the Sichuan‐Yunnan block, and stresses accumulate on the QJF and SJF The current movement of the Xiaojiang fault may not cut through the Red River fault and continue southward

Numerical modeling is used to understand the regional scale flow dynamics of the fault‐hosted orogenic geothermal system at the Grimsel Mountain Pass in the Swiss Alps. The model is calibrated against observations from thermal springs discharging in a tunnel some 250 m underneath Grimsel Pass to derive estimates for the bulk permeability of the fault. Simulations confirm that without the fault as a hydraulic conductor the thermal springs would not exist. Regional topography alone drives meteoric water in a single pass through the fault plane where it penetrates to depths exceeding 10 km and acquires temperatures in excess of 250°C. Thermal constraints from the thermal springs at Grimsel Pass suggest bulk fault permeabilities in the range of 2e−15 m2–4.8e−15 m2. Reported residence times of >30,000 and 7 years for the deep geothermal and shallow groundwater components in the thermal spring water, respectively, suggest fault permeabilities of around 2.5e−15 m2. We show that the long residence time of the deep geothermal water is likely a consequence of low recharge rates during the last glaciation event in the Swiss Alps, which started some 30,000 years ago. Deep groundwater discharging at Grimsel Pass today thus infiltrated the Grimsel fault prior to the last glaciation event. The range of permeabilities estimated from observational constraints is fully consistent with a subcritical single‐pass flow system in the fault plane. Plain Language Summary Observations from warm springs discharging through a fault at Grimsel Pass (2,164 m.a.s.l.) in the Swiss Alps are used to constrain a numerical model of the deep water circulation feeding the springs. The springs are known to have been active for at least 3.3 million years and to be due to ascent of meteoric water that penetrated to depths exceeding 10 km, where it acquired temperatures above 250°C. Simulations show that the circulation along the fault connects a meteoric recharge zone at high altitude to the west with a sub‐vertical permeable discharge zone at Grimsel Pass. A key unknown is the permeability of the fault. Temperature, discharge rate and chemical composition of the spring water depend on flow conditions at depth and can be used to estimate the fault's bulk permeability. Our study shows that the range of fault permeabilities can be narrowed down to roughly half an order of magnitude: 1e−15 m2–5e−15 m2. This permeability range is consistent with a currently stable, single‐pass flow pattern. Long water‐residence times inferred from the isotopic composition of the spring water suggest low recharge rates during the last glaciation and the dominance of a multi‐pass flow pattern during that time. Key Points The topography in the Grimsel region drives meteoric water to depths exceeding 10 km, causing discharge of thermal water at Grimsel Pass Based on thermal and chemical constraints from the spring water, the bulk fault permeability is in the range of 2e−15 m2–4.8e−15 m2 Recent periods of glaciation changed the pattern of flow in the fault plane and are likely the reason for fluid residence times >30,000 years