Hot spring sinters: keys to understanding Earth's earliest life forms

The question of what composed the Earth's oldest fossils is the subject of current debate. At present, taphonomical determination of Archean silicified microfossils is largely based on morphological comparisons with extant microorganisms. This method has significant shortcomings because little is known about which types of bacteria silicify, what physical changes are induced on those species during mineralization, and, most importantly, what their preservation potential is. Terrestrial hot springs may help resolve these uncertainties because the silica-supersaturated geothermal fluids mineralize a wide variety of natural microbial communities and thus lead to the formation of numerous distinct biofacies. Some of these biofacies are reminiscent of Archean siliceous stromatolites from which the oldest microfossils were recovered. We suggest that by integrating molecular techniques that characterize the indigenous microbial populations growing in different biofacies with electron microscopy, we may be able to assess better what types of ancient microbes could have become fossilized.

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

Microorganisms ◽

10.3390/microorganisms9071473 ◽

2021 ◽

Vol 9 (7) ◽

pp. 1473

Author(s):

Ani Saghatelyan ◽

Armine Margaryan ◽

Hovik Panosyan ◽

Nils-Kåre Birkeland

Keyword(s):

16S Rrna ◽

Microbial Diversity ◽

High Altitude ◽

Hot Springs ◽

Hot Spring ◽

Abiotic Factors ◽

Rrna Gene ◽

Geothermal Springs ◽

Bacterial Phyla ◽

Terrestrial Hot Springs

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.

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Spatial Metagenomics of Three Geothermal Sites in Pisciarelli Hot Spring Focusing on the Biochemical Resources of the Microbial Consortia

Molecules ◽

10.3390/molecules25174023 ◽

2020 ◽

Vol 25 (17) ◽

pp. 4023

Author(s):

Roberta Iacono ◽

Beatrice Cobucci-Ponzano ◽

Federica De Lise ◽

Nicola Curci ◽

Luisa Maurelli ◽

...

Keyword(s):

Hot Springs ◽

Hot Spring ◽

Microbial Community Composition ◽

Chemical Properties ◽

Microbial Consortia ◽

Comprehensive Information ◽

Geothermal Activity ◽

Terrestrial Hot Springs ◽

Metagenomic Study ◽

Mechanisms Of Adaptation

Terrestrial hot springs are of great interest to the general public and to scientists alike due to their unique and extreme conditions. These have been sought out by geochemists, astrobiologists, and microbiologists around the globe who are interested in their chemical properties, which provide a strong selective pressure on local microorganisms. Drivers of microbial community composition in these springs include temperature, pH, in-situ chemistry, and biogeography. Microbes in these communities have evolved strategies to thrive in these conditions by converting hot spring chemicals and organic matter into cellular energy. Following our previous metagenomic analysis of Pisciarelli hot springs (Naples, Italy), we report here the comparative metagenomic study of three novel sites, formed in Pisciarelli as result of recent geothermal activity. This study adds comprehensive information about phylogenetic diversity within Pisciarelli hot springs by peeking into possible mechanisms of adaptation to biogeochemical cycles, and high applicative potential of the entire set of genes involved in the carbohydrate metabolism in this environment (CAZome). This site is an excellent model for the study of biodiversity on Earth and biosignature identification, and for the study of the origin and limits of life.

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Taxonomic fidelity of silicified filamentous microbes from hot-spring systems in the Taupo Volcanic Zone, North Island, New Zealand

Transactions of the Royal Society of Edinburgh Earth Sciences ◽

10.1017/s0263593300000821 ◽

2003 ◽

Vol 94 (4) ◽

pp. 475-483 ◽

Cited By ~ 16

Author(s):

Brian Jones ◽

Robin W. Renaut ◽

Michael R. Rosen

Keyword(s):

New Zealand ◽

Hot Springs ◽

Hot Spring ◽

Morphological Characteristics ◽

Colony Morphology ◽

Taupo Volcanic Zone ◽

Volcanic Zone ◽

The North ◽

Preservation Potential ◽

Physical Changes

ABSTRACTModern, silica-precipitating hot springs, like those found in the Taupo Volcanic Zone (TVZ) on the North Island of New Zealand, are natural laboratories for assessing microbial silicification. Many of the silicified microbes found in the siliceous sinters of these spring systems seem to be life-like replicas of the original microbes. Such preservation reflects the fact that many of the microbes are replaced and encrusted by opal-A before they are destroyed by desiccation and decay. The taxonomic fidelity of these silicified microbes depends on the preservation potential of those features which are needed to identify them. For example, identification of extant cyanobacteria, relies on as many as 37 different features, most of which are not preserved by silicification.In the hot-spring systems of the TVZ, characterisation of cyanobacteria which have been replaced and encrusted by opal-A is typically restricted to colony morphology, the length, diameter and morphology of the filament, and the presence/absence of septa, branching or a sheath. In many cases, description is limited to a subset of these parameters. Such a limited set of morphological characteristics severely impedes identifications in terms of extant taxa. The physical changes which accompany the stepwise diagenetic progression from opal-A to opal-CT ± opal-C to microcrystalline quartz may lead to further degradation of the silicified microbes and the loss of more taxonomically important features. Clearly, considerable care must be taken when trying to name silicified microorganisms and make palaeoenvironmental inferences.

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Diversity and Distribution of Culturable Thermus Species in Terrestrial Hot Springs of Southwestern Yunnan Province in China

Diversity ◽

10.3390/d13090455 ◽

2021 ◽

Vol 13 (9) ◽

pp. 455

Author(s):

Yongxia Wang ◽

Canhai Xu ◽

Long Han ◽

Chengpeng Li ◽

Wei Xiao ◽

...

Keyword(s):

Principal Component Analysis ◽

Yunnan Province ◽

Hot Springs ◽

Hot Spring ◽

Principal Component ◽

Geothermal Area ◽

Culturable Bacterium ◽

Thermal Environments ◽

Terrestrial Hot Springs ◽

Geothermal Region

The Yunnan geothermal area has many neutral and alkalescent thermal springs. Members of the genus Thermus have been found in thermal environments. In this study, we attempted to cultivate numerically abundant Thermus species using a variety of different strategies. A total of 223 strains of Thermus-like bacteria were isolated from seventeen hot spring samples of four geothermal regions (Baoshan, Dali, Lincang and Dehong). These strains were classified into two genera, Thermus and Meiothermus, based on 16S rDNA. The optimal isolation temperature of the Thermus genus was 63–70 °C. The highest Thermus diversity was found at 63 °C. Thermus brockianus was a universal culturable bacterium in the four geothermal regions. The principal component analysis (PCA) showed that T. oshimai preferred to inhabit the hot springs of the Baoshan (Bs) geothermal region, and T. amyloliquefaciens dominated the Dali (Dl) geothermal region, whereas T. tengchongensis accumulated in the Lincang (Lc) and Dehong (Dh) geothermal regions. The results suggested that Thermus species had habitat-preferable characteristics among the four geothermal regions. The findings may help identify the niche from which Thermus strains can likely be isolated.

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Silica Precipitation in a Wet–Dry Cycling Hot Spring Simulation Chamber

Life ◽

10.3390/life10010003 ◽

2020 ◽

Vol 10 (1) ◽

pp. 3 ◽

Cited By ~ 2

Author(s):

Andrew Gangidine ◽

Jeff R. Havig ◽

Jeffrey S. Hannon ◽

Andrew D. Czaja

Keyword(s):

Hot Springs ◽

Hot Spring ◽

High Surface ◽

Chemical Components ◽

Early Earth ◽

Chemical Complexity ◽

Silica Precipitation ◽

Dry Conditions ◽

Terrestrial Hot Springs ◽

Simulation Chamber

Terrestrial hot springs have emerged as strong contenders for sites that could have facilitated the origin of life. Cycling between wet and dry conditions is a key feature of these systems, which can produce both structural and chemical complexity within protocellular material. Silica precipitation is a common phenomenon in terrestrial hot springs and is closely associated with life in modern systems. Not only does silica preserve evidence of hot spring life, it also can help it survive during life through UV protection, a factor which would be especially relevant on the early Earth. Determining which physical and chemical components of hot springs are the result of life vs. non-life in modern hot spring systems is a difficult task, however, since life is so prevalent in these environments. Using a model hot spring simulation chamber, we demonstrate a simple yet effective way to precipitate silica with or without the presence of life. This system may be valuable in further investigating the plausible role of silica precipitation in ancient terrestrial hot spring environments even before life arose, as well as its potential role in providing protection from the high surface UV conditions which may have been present on early Earth.

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Global Occurrence of Archaeal amoA Genes in Terrestrial Hot Springs

Applied and Environmental Microbiology ◽

10.1128/aem.00843-08 ◽

2008 ◽

Vol 74 (20) ◽

pp. 6417-6426 ◽

Cited By ~ 138

Author(s):

Chuanlun L. Zhang ◽

Qi Ye ◽

Zhiyong Huang ◽

WenJun Li ◽

Jinquan Chen ◽

...

Keyword(s):

Microbial Mats ◽

Hot Springs ◽

Hot Spring ◽

Large Subunit ◽

The United States ◽

Group Method ◽

Soil System ◽

Water Columns ◽

Terrestrial Hot Springs ◽

Cluster A

ABSTRACT Despite the ubiquity of ammonium in geothermal environments and the thermodynamic favorability of aerobic ammonia oxidation, thermophilic ammonia-oxidizing microorganisms belonging to the crenarchaeota kingdom have only recently been described. In this study, we analyzed microbial mats and surface sediments from 21 hot spring samples (pH 3.4 to 9.0; temperature, 41 to 86°C) from the United States, China, and Russia and obtained 846 putative archaeal ammonia monooxygenase large-subunit (amoA) gene and transcript sequences, representing a total of 41 amoA operational taxonomic units (OTUs) at 2% identity. The amoA gene sequences were highly diverse, yet they clustered within two major clades of archaeal amoA sequences known from water columns, sediments, and soils: clusters A and B. Eighty-four percent (711/846) of the sequences belonged to cluster A, which is typically found in water columns and sediments, whereas 16% (135/846) belonged to cluster B, which is typically found in soils and sediments. Although a few amoA OTUs were present in several geothermal regions, most were specific to a single region. In addition, cluster A amoA genes formed geographic groups, while cluster B sequences did not group geographically. With the exception of only one hot spring, principal-component analysis and UPGMA (unweighted-pair group method using average linkages) based on the UniFrac metric derived from cluster A grouped the springs by location, regardless of temperature or bulk water pH, suggesting that geography may play a role in structuring communities of putative ammonia-oxidizing archaea (AOA). The amoA genes were distinct from those of low-temperature environments; in particular, pair-wise comparisons between hot spring amoA genes and those from sympatric soils showed less than 85% sequence identity, underscoring the distinctness of hot spring archaeal communities from those of the surrounding soil system. Reverse transcription-PCR showed that amoA genes were transcribed in situ in one spring and the transcripts were closely related to the amoA genes amplified from the same spring. Our study demonstrates the global occurrence of putative archaeal amoA genes in a wide variety of terrestrial hot springs and suggests that geography may play an important role in selecting different assemblages of AOA.

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Productivity and Community Composition of Low Biomass/High Silica Precipitation Hot Springs: A Possible Window to Earth’s Early Biosphere?

Life ◽

10.3390/life9030064 ◽

2019 ◽

Vol 9 (3) ◽

pp. 64 ◽

Cited By ~ 2

Author(s):

Jeff R. Havig ◽

Trinity L. Hamilton

Keyword(s):

Microbial Communities ◽

Hot Springs ◽

Hot Spring ◽

Physical Parameters ◽

Total Biomass ◽

Martian Surface ◽

Silica Precipitation ◽

Terrestrial Hot Springs ◽

High Silica ◽

Oxygenic Phototrophs

Terrestrial hot springs have provided a niche space for microbial communities throughout much of Earth’s history, and evidence for hydrothermal deposits on the Martian surface suggest this could have also been the case for the red planet. Prior to the evolution of photosynthesis, life in hot springs on early Earth would have been supported though chemoautotrophy. Today, hot spring geochemical and physical parameters can preclude the occurrence of oxygenic phototrophs, providing an opportunity to characterize the geochemical and microbial components. In the absence of the photo-oxidation of water, chemoautotrophy in these hot springs (and throughout Earth’s history) relies on the delivery of exogenous electron acceptors and donors such as H2, H2S, and Fe2+. Thus, systems fueled by chemoautotrophy are likely energy substrate-limited and support low biomass communities compared to those where oxygenic phototrophs are prevalent. Low biomass silica-precipitating systems have implications for preservation, especially over geologic time. Here, we examine and compare the productivity and composition of low biomass chemoautotrophic versus photoautotrophic communities in silica-saturated hot springs. Our results indicate low biomass chemoautotrophic microbial communities in Yellowstone National Park are supported primarily by sulfur redox reactions and, while similar in total biomass, show higher diversity in anoxygenic phototrophic communities compared to chemoautotrophs. Our data suggest productivity in Archean terrestrial hot springs may be directly linked to redox substrate availability, and there may be high potential for geochemical and physical biosignature preservation from these communities.

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Hydrogeological regime and groundwater occurence in the Anthemountas River Basin

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11104 ◽

2017 ◽

Vol 47 (2) ◽

pp. 711 ◽

Cited By ~ 3

Author(s):

N. Kazakis ◽

K. Voudouris ◽

G. Vargemezis ◽

A. Pavlou

Keyword(s):

River Basin ◽

Carbonate Rocks ◽

Hot Springs ◽

Cold Water ◽

Karst Aquifer ◽

Northern Greece ◽

Water Demands ◽

Geothermal Fluids ◽

Porous Aquifers

The Anthemountas river basin is located in northern Greece and covers an area of 374 km2. The mountainous part of the basin consists of ophiolitic, crystalline and carbonate rocks, whereas the lowlands comprise Neogene and Quaternary sediments. Porous aquifers are developed in neogene and quaternary deposits of confined and/or unconfined conditions. Karstic aquifers are developed in the carbonate rocks and there are aquifers in the Mesozoic and Palaeozoic fissured rocks. The water demands of the basin are mainly met by the exploitation of the porous aquifers through a large number of boreholes (more than 1000). The aquifers of fissured rocks discharge through cold springs without significant flow rate. Thermal hot springs are recorded across the Anthemountas fault discharging a mixture of geothermal fluids and cold water from the karst aquifer. According to their hydrogeological and lithological characteristics, porous aquifers can be divided into the subsystems of Galatista and Galarinos in the eastern part of the Anthemountas basin, Vasilika-Risio-Thermi and Tagardes-Trilofos in the western part and Peraia-Agia Triada and AUTh farm-Makedonia airport in the coastal area. For the determination of the aquifers (geometry and anatomy), their recharge mechanisms and hydraulic connection, data from geological maps, lithological profiles, geoelectrical soundings and tomographies, pumping tests and groundwater level measurements are used.

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Geofluids Assessment of the Ayub and Shafa Hot Springs in Kopet-Dagh Zone (NE Iran): An Isotopic Geochemistry Approach

Geofluids ◽

10.1155/2017/6358680 ◽

2017 ◽

Vol 2017 ◽

pp. 1-11 ◽

Cited By ~ 4

Author(s):

Hossein Mohammadzadeh ◽

Majid Kazemi

Keyword(s):

Geothermal Energy ◽

Hot Springs ◽

Hot Spring ◽

Environmental Isotopes ◽

Geothermal Gradient ◽

Deep Circulation ◽

Wide Range ◽

Kopet Dagh ◽

Ne Iran

Geothermal energy has a wide range of uses in our life. It is very important to characterize the temperature and the depth of geothermal reservoirs. The aim of this paper is the determination of type, origin source of water temperature, and depth of water circulation in the Ayub-Peighambar and Shafa (AP and SH) hot springs, located in NE Iran, using hydrogeochemistry and environmental isotopes (2H and18O). AP hot spring has elevated temperature (36–40°C) and as such is very important for balneotherapy and geotourism industry purposes. The average values ofδ18O andδ2H for this hot spring (−10‰and −73‰, resp.) are analogous to that of geothermal and meteoric waters. This indicates that the heat source cannot be related to volcanic activities (with averageδ18O value of about 5‰) and it is most probably associated with geothermal gradient with deep circulation of groundwater through faults. Based on Na-K geothermometers coupled with isotopic (18O and2H) geochemistry the temperature of the AP geothermal reservoir was estimated to be in the range of 100–150°C with 3–5 and 4.2 kilometres’ depth, respectively. Chemically, the AP samples are CaSO4facies with a chemically homogeneous source and steam heated waters type.

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Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits

Nature Communications ◽

10.1038/ncomms15263 ◽

2017 ◽

Vol 8 (1) ◽

Cited By ~ 91

Author(s):

Tara Djokic ◽

Martin J. Van Kranendonk ◽

Kathleen A. Campbell ◽

Malcolm R. Walter ◽

Colin R. Ward

Keyword(s):

Carbon Isotopes ◽

Hydrothermal Fluid ◽

Hot Springs ◽

Hot Spring ◽

Convincing Evidence ◽

Fluid Circulation ◽

Terrestrial Hot Springs ◽

Exopolymeric Substance ◽

Volcanic Caldera ◽

Pilbara Craton

Abstract The ca. 3.48 Ga Dresser Formation, Pilbara Craton, Western Australia, is well known for hosting some of Earth’s earliest convincing evidence of life (stromatolites, fractionated sulfur/carbon isotopes, microfossils) within a dynamic, low-eruptive volcanic caldera affected by voluminous hydrothermal fluid circulation. However, missing from the caldera model were surface manifestations of the volcanic-hydrothermal system (hot springs, geysers) and their unequivocal link with life. Here we present new discoveries of hot spring deposits including geyserite, sinter terracettes and mineralized remnants of hot spring pools/vents, all of which preserve a suite of microbial biosignatures indicative of the earliest life on land. These include stromatolites, newly observed microbial palisade fabric and gas bubbles preserved in inferred mineralized, exopolymeric substance. These findings extend the known geological record of inhabited terrestrial hot springs on Earth by ∼3 billion years and offer an analogue in the search for potential fossil life in ancient Martian hot springs.

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