Comparative Metagenomic Analysis of Two Hot Springs From Ourense (Northwestern Spain) and Others Worldwide

With their circumneutral pH and their moderate temperature (66 and 68°C, respectively), As Burgas and Muiño da Veiga are two important human-use hot springs, previously studied with traditional culture methods, but never explored with a metagenomic approach. In the present study, we have performed metagenomic sequence-based analyses to compare the taxonomic composition and functional potential of these hot springs. Proteobacteria, Deinococcus-Thermus, Firmicutes, Nitrospirae, and Aquificae are the dominant phyla in both geothermal springs, but there is a significant difference in the abundance of these phyla between As Burgas and Muiño da Veiga. Phylum Proteobacteria dominates As Burgas ecosystem while Aquificae is the most abundant phylum in Muiño da Veiga. Taxonomic and functional analyses reveal that the variability in water geochemistry might be shaping the differences in the microbial communities inhabiting these geothermal springs. The content in organic compounds of As Burgas water promotes the presence of heterotrophic populations of the genera Acidovorax and Thermus, whereas the sulfate-rich water of Muiño da Veiga favors the co-dominance of genera Sulfurihydrogenibium and Thermodesulfovibrio. Differences in ammonia concentration exert a selective pressure toward the growth of nitrogen-fixing bacteria such as Thermodesulfovibrio in Muiño da Veiga. Temperature and pH are two important factors shaping hot springs microbial communities as was determined by comparative analysis with other thermal springs.

Microbial Diversity of Terrestrial Geothermal Springs in Armenia and Nagorno-Karabakh: A Review

The microbial diversity of high-altitude geothermal springs has been recently assessed to explore their biotechnological potential. However, little is known regarding the microbiota of similar ecosystems located on the Armenian Highland. This review summarizes the known information on the microbiota of nine high-altitude mineralized geothermal springs (temperature range 25.8–70 °C and pH range 6.0–7.5) in Armenia and Nagorno-Karabakh. All these geothermal springs are at altitudes ranging from 960–2090 m above sea level and are located on the Alpide (Alpine–Himalayan) orogenic belt, a seismically active region. A mixed-cation mixed-anion composition, with total mineralization of 0.5 mg/L, has been identified for these thermal springs. The taxonomic diversity of hot spring microbiomes has been examined using culture-independent approaches, including denaturing gradient gel electrophoresis (DGGE), 16S rRNA gene library construction, 454 pyrosequencing, and Illumina HiSeq. The bacterial phyla Proteobacteria, Bacteroidetes, Cyanobacteria, and Firmicutes are the predominant life forms in the studied springs. Archaea mainly include the phyla Euryarchaeota, Crenarchaeota, and Thaumarchaeota, and comprise less than 1% of the prokaryotic community. Comparison of microbial diversity in springs from Karvachar with that described for other terrestrial hot springs revealed that Proteobacteria, Bacteroidetes, Actinobacteria, and Deinococcus–Thermus are the common bacterial groups in terrestrial hot springs. Contemporaneously, specific bacterial and archaeal taxa were observed in different springs. Evaluation of the carbon, sulfur, and nitrogen metabolism in these hot spring communities has revealed diversity in terms of metabolic activity. Temperature seems to be an important factor in shaping the microbial communities of these springs. Overall, the diversity and richness of the microbiota are negatively affected by increasing temperature. Other abiotic factors, including pH, mineralization, and geological history, also impact the structure and function of the microbial community. More than 130 bacterial and archaeal strains (Bacillus, Geobacillus, Parageobacillus, Anoxybacillus, Paenibacillus, Brevibacillus Aeribacillus, Ureibacillus, Thermoactinomyces, Sporosarcina, Thermus, Rhodobacter, Thiospirillum, Thiocapsa, Rhodopseudomonas, Methylocaldum, Desulfomicrobium, Desulfovibrio, Treponema, Arcobacter, Nitropspira, and Methanoculleus) have been reported, some of which may be representative of novel species (sharing 91–97% sequence identity with their closest matches in GenBank) and producers of thermozymes and biomolecules with potential biotechnological applications. Whole-genome shotgun sequencing of T. scotoductus K1, as well as of the potentially new Treponema sp. J25 and Anoxybacillus sp. K1, were performed. Most of the phyla identified by 16S rRNA were also identified using metagenomic approaches. Detailed characterization of thermophilic isolates indicate the potential of the studied springs as a source of biotechnologically valuable microbes and biomolecules.

Regional structures influencing the groundwater geochemistry around geothermal springs: A case study from Padiyathalawa, Sri Lanka

<p>Hydro-geochemistry of groundwater plays an important role in understanding the characteristics of a geothermal system. Mixing zones of geothermal deep waters and shallow groundwater can be identified through chemical distribution maps and help identify geothermal flow paths. The flow paths can be used to calculate the chemical values of the geothermal water leading to a characterization of the heat source. In combination with knowledge about regional structures, the geochemical distribution can further reveal unknown geothermal zones.</p><p>In the present study, the geochemical distribution of the groundwater is studied from samples collected from shallow and deep wells, with special reference to the regional structures present in the terrain. The study area was selected as a 20 • 20 km area centered around the Padiyathalawa hot spring field in Sri Lanka. From the results, two main geochemical anomalous zones are identified, especially with the increased values of electrical conductivity (EC), total dissolved solids (TDS), and Sulphate distribution maps. Those two zones include the hot spring itself as well as an area in ~10 km distance in the NE direction from the hot spring. Both zones are characterized by crosscutting structures of dolerite dykes and shear zones. Due to the shear zones, there are deep-seated fractures facilitating water flow from deeper layers towards the surface. This uprising water mixes with the shallow groundwater, affecting the general geochemical values of the shallow groundwater system.</p><p>Common minerals in Dolerite in Sri Lanka are Pyroxenes, Feldspar, Ilmenite, Magnetite, and Pyrite with minor amounts of other minerals. The increased EC values in both before mentioned zones relate with higher amounts of iron due to dissolution and mixing processes in regions with fractured Dolerite. Similarly, the increased concentration of Sulphates in the groundwater can be related to Pyrite from the fractured Dolerite, as microbial oxidization of Pyrite leads to origin of Sulphates. The increase of TDS can be interpreted as shallow water mixing with deep geothermal water, which contains a higher amount of minerals from the fractured dolerites.</p><p>The similar geochemical anomalies in those two zones can be associated with cross-cutting Dolerite dikes and existing faults in the shear zones at greater depth, subsequently mixing uprising deep geothermal water with shallow groundwater. A similar geochemistry and tectonic setting suggest similar flow paths from the underground and therefore also similar geothermal conditions at both spots. However, due to the rural and remote region, only one of the two before mentioned areas is known as a hot spring field. Thermal signatures dissipate much more quickly in the shallow groundwater than the mineral composition and might not be significant for measurement. Geochemical signatures of groundwater can therefore be a substantial help to locate geothermal springs, identify source mechanisms and characterize fluid flow paths.</p>