Abstract
Background
Gypsum Hill Spring, located in Nunavut in the Canadian High Arctic, is a rare example of a cold saline spring arising through thick permafrost. It perennially discharges cold (~ ...7 °C), hypersaline (7–8% salinity), anoxic (~ 0.04 ppm O
2
), and highly reducing (~ − 430 mV) brines rich in sulfate (2.2 g.L
−1
) and sulfide (9.5 ppm), making Gypsum Hill an analog to putative sulfate-rich briny habitats on extraterrestrial bodies such as Mars.
Results
Genome-resolved metagenomics and metatranscriptomics were utilized to describe an active microbial community containing novel metagenome-assembled genomes and dominated by sulfur-cycling
Desulfobacterota
and
Gammaproteobacteria
. Sulfate reduction was dominated by hydrogen-oxidizing chemolithoautotrophic
Desulfovibrionaceae
sp. and was identified in phyla not typically associated with sulfate reduction in novel lineages of
Spirochaetota
and
Bacteroidota
. Highly abundant and active sulfur-reducing
Desulfuromusa
sp. highly transcribed non-coding RNAs associated with transcriptional regulation, showing potential evidence of putative metabolic flexibility in response to substrate availability. Despite low oxygen availability, sulfide oxidation was primarily attributed to aerobic chemolithoautotrophic
Halothiobacillaceae
. Low abundance and transcription of photoautotrophs indicated sulfur-based chemolithoautotrophy drives primary productivity even during periods of constant illumination.
Conclusions
We identified a rare surficial chemolithoautotrophic, sulfur-cycling microbial community active in a unique anoxic, cold, hypersaline Arctic spring. We detected Mars-relevant metabolisms including hydrogenotrophic sulfate reduction, sulfur reduction, and sulfide oxidation, which indicate the potential for microbial life in analogous S-rich brines on past and present Mars.
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.
Monte Conca Cave is a karst system placed in Messinian evaporites, consisting of an active cave and a resurgence located on the massif of Monte Conca, Campofranco within the "Riserva Naturale ...Integrale di Monte Conca". To characterize the physical and chemical parameters of the Monte Conca Cave and of the sulfidic spring, air temperature, relative humidity, water pH, and concentrations of dissolved sulfides, nitrates and sulfates were monitored. The high sulfide consumption rate in the sulfidic spring, evaluated by a kinetic study, suggests that biotic consumption is dominant. Iron content was also evaluated in water and snottites, given its involvement in microbial activity. The microbial mats could be the source of an autotrophic system in close correlation with the biological cycle of many species of living organisms found near the spring. Some of them show typical troglobitic characteristics, while the presence and abundance of others depends on the water amount. The greater abundance of taxa found close to the sulfidic spring suggests a complex food web associated with it.
Recently, a unique microbial community, growing in a whitish, macroscopically visible strings-of-pearls-like structure was discovered in the cold, sulfidic marsh water of the Sippenauer Moor near ...Regensburg, Bavaria, Germany. The pearls interior is predominated by microcolonies of the non-methanogenic SM1 euryarchaeon; the outer part of the pearls is mainly composed of
Thiothrix. To screen sulfidic ecosystems for the distribution of such unique microbial communities, comparative microbial and geochemical analyses of cold, sulfidic springs of three geographically distinct locations in Bavaria, Germany, and Dalyan, Turkey, were performed. Here, we report on the discovery and study of another type of strings-of-pearls revealing a new microbial community structure. While the SM1 euryarchaeon is again the predominant archaeal constituent, the bacterial partner is the so-called IMB1 ε-proteobacterium. Due to the predominance of the IMB1 ε-proteobacterium, the strings-of-pearls reveal a fluffy and greyish macroscopical appearance. The phylogenetic survey revealed SM1 euryarchaeal relatives, designated as SM1 group, in all sites studied, indicating a widespread distribution of these archaea in terrestrial ecosystems.
Most transformations within the sulfur cycle are controlled by the biosphere, and deciphering the abiotic and biotic nature and turnover of sulfur is critical to understand the geochemical and ...ecological changes that have occurred throughout the Earth's history. Here, synchrotron radiation-based sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to examine sulfur speciation in natural microbial mats from two aphotic (cave) settings. Habitat geochemistry, microbial community compositions, and sulfur isotope systematics were also evaluated. Microorganisms associated with sulfur metabolism dominated the mats, including members of the Epsilonproteobacteria and Gammaproteobacteria. These groups have not been examined previously by sulfur K-edge XANES. All of the mats consisted of elemental sulfur, with greater contributions of cyclo-octasulfur (S₈) compared with polymeric sulfur (Sμ). While this could be a biological fingerprint for some bacteria, the signature may also indicate preferential oxidation of Sμ and S₈ accumulation. Higher sulfate content correlated to less S₈ in the presence of Epsilonproteobacteria. Sulfur isotope compositions confirmed that sulfur content and sulfur speciation may not correlate to microbial metabolic processes in natural samples, thereby complicating the interpretation of modern and ancient sulfur records.
Barite (BaSO4) is a highly stable and widely-distributed mineral found in magmatic, metamorphic, and sedimentary rocks of all ages, as well as in soils, aerosol dust, and extraterrestrial material. ...Barite can form in a variety of settings in the oceans (hydrothermal deposits, cold seeps, water column, or within sediments) and on the continents (soils, sulfidic springs and in the subsurface) when (1) two fluids mix – one containing barium and another containing sulfate, (2) sulfur is oxidized forming sulfate in a barium containing solution, or (3) barium or sulfate is concentrated in microenvironments where either sulfate or barium are already present. Hydrologic and biologic processes can therefore play key roles in the formation of barite and affect its geochemical composition. Characteristics of barite from various modern settings are identified here to serve as analogs for ancient systems, summarizing previous work and adding new details from the pelagic marine, hydrothermal, cold seep and continental setting. Radiogenic strontium in barite clearly identifies the source(s) of fluid forming barite with the most radiogenic values measured in continental sulfidic spring settings associated with a deep fluid component that interacts with ancient crustal rocks. Sulfur and oxygen isotopes can distinguish between sources of sulfate and identify settings where the influence of (bio)chemical processes such as sulfate reduction is prominent. There are no unique stable strontium isotopic signatures for barite formed in any of the settings investigated here, but Holocene coretop marine pelagic barite appears to have a constant offset from seawater of approximately −0.53‰ in coretop samples in contrast to the wide range of values in barite precipitated in other settings. Stable strontium mass dependent fractionation could be useful in understanding post-depositional and diagenetic processes such as authigenic precipitation and recrystallization.
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•Hydrologic, biologic processes play key roles in barite formation and geochemistry.•Sulfur and oxygen isotopes distinguish sulfate sources and (bio)chemical processes.•Radiogenic Sr identifies fluid sources, stable Sr isotopic signatures are not unique.•Marine pelagic barite stable Sr isotopes have consistent offset from seawater.
Due to the limited cultivability of the vast majority of microorganisms, researchers have applied environmental genomics and other state-of-the-art technologies to gain insights into the biology of ...uncultivated Archaea and bacteria in their natural biotope. In this review, we summarize the scientific findings on a recently proposed order-level lineage of uncultivated Archaea called Altiarchaeales, which includes "Candidatus Altiarchaeum hamiconexum" as the most well-described representative. Ca. A. hamiconexum possesses a complex biology: thriving strictly anaerobically, this microorganism is capable of forming highly-pure biofilms, connecting the cells by extraordinary cell surface appendages (the "hami") and has other highly unusual traits, such as a double-membrane-based cell wall. Indicated by genomic information from different biotopes, the Altiarchaeales seem to proliferate in deep, anoxic groundwater of Earth's crust bearing a potentially very important function: carbon fixation. Although their net carbon fixation rate has not yet been determined, they appear as highly abundant organisms in their biotopes and may thus represent an important primary producer in the subsurface. In sum, the research over more than a decade on Ca. A. hamiconexum has revealed many interesting features of its lifestyle, its genomic information, metabolism and ultrastructure, making this archaeon one of the best-studied uncultivated Archaea in the literature.
We have documented the presence of celestine (SrSO4) within sediment accumulating at an artesian sulfidic spring (Zodletone Spring, Oklahoma) dominated by barite (BaSO4) precipitation associated with ...microbiological activity. The distribution and speciation of Sr in solid phases was determined by synchrotron-based micro-X-ray fluorescence spectroscopy and micro-X-ray diffraction, and particle morphology and texture was determined using electron microscopy. In all the natural sulfidic spring samples and lithified tufa sample, celestine was detected in fine-grained micron-scale Sr-rich phases but not in euhedral, Sr-poor grains. In parallel laboratory-based precipitation experiments, celestine was not observed even when solutions contained high Sr/Ba. Thermodynamic predictions alone do not account for the presence of micron-scale celestine in the sulfidic spring, and they do not account for the differences in Sr presence and distribution in naturally-occurring versus synthetic grains. While the mechanism is unclear, based on this evidence we hypothesize that the combination of bacterial surfaces and microenvironments within the crusts and microbial mats creates a synergistic effect where Sr is preferentially exchanged over Ba between the overlying stream water and the pore water within the mats allowing celestine to precipitate. Ultimately, our results point to an important role of biological activity for preferential Sr uptake. The presence of micron-scale celestine in ancient barite deposits can therefore potentially be used as a biomarker for conditions similar to modern sulfidic springs.
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Mercury rich geothermal springs are likely environments where mercury resistance is critical to microbial life and where microbe-mercury interactions may have evolved. Eleven facultative thermophilic ...and chemolithoautotrophic, thiosulfate oxidizing bacteria were isolated from thiosulfate enrichments of biofilms from mercury rich hot sulfidic springs in Mount Amiata, Italy. Some strains were highly resistant to mercury (>=200 μM HgCl₂) regardless of its presence or absence during primary enrichments, and three reduced ionic mercury to its elemental form. The gene encoding for the mercuric reductase enzyme (MerA), was amplified by PCR from seven strains. However, one highly resistant strain did not reduce mercury nor carried merA, suggesting an alternative resistance mechanism. All strains were members of the order Bacillales and were most closely related to previously described thermophiles belonging to the Firmicutes. Phylogenetic analyses clustered the MerA of the isolates in two supported novel nodes within the Firmicutes lineage and a comparison with the 16S rRNA gene tree suggested at least one case of horizontal gene transfer. Overall, the results show that the thermophilic thiosulfate oxidizing isolates were adapted to life in presence of mercury mostly, but not exclusively, by possessing MerA. These findings suggest that reduction of mercury by chemolithotrophic thermophilic bacteria may mobilize mercury from sulfur and iron deposits in geothermal environments.
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