Volume 8 - 2021 | https://doi.org/10.3389/fmars.2021.715335 This article is part of the Research TopicMarine EpibiosesView all 15 articles The hypersaline lagoon system of Araruama (HLSA) is one of the largest in the world and one of the most important sources of evaporative salt in Brazil The biogeochemical characteristics of this lagoon system led it to be considered a Precambrian relic The HLSA also harbors extensive microbial mats but the taxonomic and metabolic attributes of these mats are poorly understood Our high-throughput metagenomics analyses demonstrated that the HLSA microbial mats are dominated by Proteobacteria Deltaproteobacteria comprises approximately 40% of the total population and it includes sulfate-reducing bacteria such as Desulfobacterales Differing in composition and function of their reaction centers other phylogenetic diverse anoxygenic phototrophic bacteria were detected in the HLSA microbial mats metagenomes and aerobic heterotrophs suggests the existence of numerous cooperative niches that are coupled and regulated by microbial interactions We suggest that the HLSA microbial mats hold microorganisms and the necessary machinery (genomic repertoire to sustain metabolic pathways) to promote favorable conditions (i.e. create an alkaline pH microenvironment) for microbially mediated calcium carbonate precipitation process nov.) obtained support the relevance of Sulfur metabolism and they are enriched with genes involved in the osmoadaptive networks hinting at possible strategies to withstand osmotic stress Metabolically versatile bacteria populations able to use multiple nutrient sources and osmolytes seem to be a relevant attribute to survive under such stressful conditions These characteristics allow microbial mats to thrive in a variety of harsh environments around the world including hypersaline ecosystems where intense evaporation and low levels of freshwater input lead to high salt concentrations in the water together with strong daily fluctuations of temperature and desiccation make this shallow system a harsh environment for any organism These shifts impose important challenges for the ecosystem function such as how microbial communities adapt to stay active while maintaining the characteristic structure of vertically stratified groups of microorganisms Anthropogenic activities also impose pressure on water quality in these lagoons Understanding how the HLSA microbial mats are characterized is crucial to provide insights of the system and allow to monitor changes of microbial diversity in these unique ecosystems We also sought to investigate the metabolic pathways enabling these microbes to thrive in such a unique environment by shedding light on the genomic repertoire related to osmoadaptation (C) An excised fraction of the microbial mat ecosystem from the hypersaline lagoon system of Araruama The microbial mats were taken at different stages of maturity or stratification Samples were collected with a small shovel and sterile metal spatulas which were sterilized with ethanol and flame between samples transferred to polypropylene tubes in the field and stored in liquid nitrogen Samples comprised a mixture of the different layers The samples were separately ground in liquid nitrogen using ceramic mortars and pestles that were washed with SDS detergent Approximately 200 mg of each sample were used for DNA extraction with the DNeasy PowerSoil Kit (Qiagen DNA integrity was evaluated by 1% agarose gel electrophoresis (GelRedTM and DNA purity was assessed with a NanoDrop spectrophotometer (Thermo Fisher Scientific Inc. The DNA was quantified with a Qubit® 3.0 Fluorometer (Life Technologies-Invitrogen Metagenomic libraries were prepared with the Nextera XT DNA Sample Preparation Kit (Illumina Library size distribution was evaluated with a 2100 Bioanalyzer (Agilent and library quantification was carried out with a 7500 Real-Time PCR System (Applied Biosystems United States) and KAPA Library Quantification Kit (Kapa Biosystems Paired-end sequencing (2 × 300 bp) was performed on a MiSeq System (Illumina) an accurate collection of functionally related protein families under the BioProject accession number PRJNA675017: BioSample SAMN16710161 and SAMN16710317 One thousand bootstrap replications were calculated to evaluate the relative support of the branches We sequenced a total of 13 microbial mat samples (corresponding to 12.69 million reads) from eight different HLSA locations in summer (n = 6) and winter (n = 7) (Table 1). After quality control, the number of metagenome sequences pairs per sample ranged from 153,231 to 1,856,780, and the total number of contigs ranged from 36,860 to 1,140,943 (Table 1) Summary statistics of quality filtering and metagenomic assembly for the hypersaline lagoon system of Araruama Taxonomic composition of the microbial mats from the hypersaline lagoon system of Araruama Bar plots depict the relative abundances of bacterial phyla (A) and genera (B) detected in the metagenomes normalized to 100% Among Proteobacteria, the most abundant groups included the orders Desulfobacterales (1.3–4.6%), Desulfovibrionales (1.5–4.1%), and Desulfuromonadales (1.0–2.8%) and the genera Rhodobacter (0.4–1.8%), Rhodopseudomonas (0.3–0.8%), and Nitrosococcus (0.4–1.0%) (Figure 2B) likely because of the importance of their metabolic roles the difference in the profile abundance was attributed to an increase in reads associated with the orders Chroococcales (4.2–10.4%) and Oscillatoriales (2.1–14.6%) The cyanobacterium genus Coleofasciculus (formerly Microcoleus) was the most abundant genus in most metagenomes (0.6–11.6%) and the species Coleofasciculus chthonoplastes alone represented 23.6% of the total abundance of Cyanobacteria (ranging from 6.4 to 39.9%; n = 95,995) Vermelha winter) were detected in all HLSA metagenomes Most of the recovered archaeal sequences were assigned to the phylum Euryarchaeota (ranging from 0.7% in S with high relative abundances of the genera Halobacterium (0.1% in S Espinho winter) and Methanomicrobia (0.3% in S The metagenomic sequences were classified into 28 SEED subsystems (Supplementary Figure 2) a wide range of metabolic pathways which allows microbes to detect changes in the environment conditions to survive and Amino Acids and Derivatives subsystems accounted for 35% of all identified sequences Cyanobacteria were found to be a key component of this system as the main group responsible for Photosynthesis (50.9–82.4%) and the order Chroococcales alone was the main contributor of genes related to Nitrogen Fixation (6.1–27.3%) and Ammonia Assimilation (5.5–36.4%) metabolisms Proteobacteria was the main contributor of genes related to Respiration (45.3–64.4%) and Fermentation (32.4–50.0%) subsystems Genes related to Sulfur metabolism (0.5–0.8%) were attributed mainly to Proteobacteria whereas genes related to Methanogenesis metabolism were attributed mainly to the bacterial phyla Actinobacteria (0.0–61.54%) and Proteobacteria (7.69–100%) and also to the archaeal orders Methanosarcinales (0.0–30.0%) and Methanopyrales (0.0–18.18%) When examining the taxonomic profile of the HLSA metagenomes, we see that five out of the six most abundant phyla (Proteobacteria, Cyanobacteria, Bacteroidetes, Firmicutes, and Chloroflexi) (Figure 2A) contain members that are capable of oxygenic and anoxygenic reaction center-based phototrophy Metabolic versatility of specific taxa present in the HLSA metagenomes is discussed below genes related to Osmotic Stress were detected in all HLSA microbial mat metagenomes following: L-ectoine synthesis (0.01–0.05%) hyperosmotic potassium uptake (0.02–0.1%) glutathione-regulated potassium-efflux system (0.05–0.2%) and voltage-gated potassium efflux systems (0.01–0.1%) Non-metric multidimensional scaling (nMDS) plot representing the Bray–Curtis similarity of general microbial community structure composition of 68 metagenomes of microbial mats from different habitats and the arrows represent the nMDS phyla scores Hierarchical clustering and bar plots of relative abundances of the major microbial phyla found within 68 metagenomes of microbial mats from different habitats Clustering was based on Euclidian distances and Ward’s clustering method Genetic relatedness between the metagenome-assembled genomes and the most closely related reference genomes based on average amino acid identity (AAI) Osmoprotectant and osmoregulation profile in the two reconstructed genomes Key genes related to Carbon, Nitrogen, and Sulfur biogeochemical cycling were compiled and allowed delineation of the functional role of the taxa associated to the bins (Table 4). For instance, both bins encode complete and partial sulfate-reduction pathways (Table 4) potentially indicating the importance of Sulfur cycling in the HLSA microbial mats Partial recovery of a determined pathway might be a result of lack of coverage in both not complete MAGs Annotations for major metabolisms such as Sulfur (dsr and bacteriochlorophyll-based Photoautotrophy (e.g. which is associated with purple sulfur bacteria Functional genetic diversity of biogeochemical cycling (C Although bacterial isolation technique has yielded valuable biodiversity information in the past currently it provides little information which limits substantial characterization and near-complete genome bins were retrieved from the metagenomic data The HLSA microbial mats sustain taxonomically diverse assemblage of microorganisms this microorganism maintains high numbers of metabolically active heterotrophs which hold catabolic and transport capabilities Complex cyanobacterial exudates become available to the general microbial community thought those bacteria it is likely that Bacteroidetes play a key role in the degradation and cycling of mat compounds and both were abundantly present in the HLSA metagenomes Key genes related to microbial-induced calcium carbonate precipitation including the novel candidate species identified in this study the new candidate species exemplify different strategies for halotolerance as mentioned before where the genomic repertoire of such candidate microbial taxa was investigated The genomes recovered from the HLSA metagenomes support the environmental relevance of the microorganisms represented by the assemblies described in this study Hypersaline lagoon system of Araruama microbial mats have evolved to encompass high taxonomic and metabolic diversity illustrated by the autotrophic and heterotrophic guilds found in their metagenomes Cuatro Cienegas and Guerrero Negro hint to possible adaptative mechanisms to thrive in hypersaline environments High metabolic flexibility and the production of osmoprotectant compounds appear to be important for survival in the HLSA microbial mats and chemosynthesis pathways by bacterial representatives in both the HLSA microbial mats metagenomes and the recovered genomes are indicative of a diverse metabolic repertoire needed to sustain life in the HLSA A high proportion of sulfur bacteria is remarkable which includes sulfate-reducing bacteria such as Desulfobacterales comprise approximately 40% of the Proteobacteria population the most abundant phylum in the HLSA microbial mat metagenomes This result supports the relevance of sulfate-reducing bacteria in the hypersaline microbial mats of HLSA where versatile populations in synergy with other taxa cover most of the metabolic activities within the mat including the precipitation of calcium carbonate in these unique microbial structures The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/Supplementary Material and AC conceived the study and designed the experiments LO and DB processed the samples and performed DNA sequencing All authors contributed to the article and approved the submitted version Support offered by the Foundation Carlos Chagas Filho Research Support of the State of Rio de Janeiro (FAPERJ) National Counsel of Technological and Scientific Development (CNPq) and Coordination for the Improvement of Higher Education Personnel (CAPES) The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed 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Carvalho, Dos Santos Costa, Dobretsov, Coutinho, Swings, Thompson and Thompson. 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The state’s Civil Defence warned of further flooding resulted in severe flooding in multiple parts of the state in particular in the Caí and Taquari river basins Governor Eduardo Leite described the situation as “devastating” But we must stand firm to give all the support to the population” The state government has so far confirmed 37 fatalities State Civil Defence said floods and storms have impacted communities in 79 municipalities A total of 56,787 people have been affected several location recorded more than 130 mm of rain The Caí river has exceeded the highest warning level at Passo Montenegro and Barca do Caí Meanwhile the Taquari has reached above the highest danger mark at Taquari and Muçum Severe weather has also impacted areas of the neighbouring state of Santa Catarina where Brazil’s national Civil Defence report 20 municipalities affected and 1 fatality The state Civil Defence reported storms brought heavy rainfall and strong winds from 02 to 04 September including rainfall accumulations of up to 150 mm on the South Coast and wind gusts of 122 km/h in Serra and 113 km/h in Xanxerê A suspected tornado was reported in the community of Anta Morta in the municipality of Santa Cecília Richard Davies is the founder of floodlist.com and reports on flooding news Cookies | Privacy | Contacts © Copyright 2025 FloodList Parts of Brazil’s livestock areas may need to import U.S Agricultural reporter based in Porto Alegre Metrics details Viruses are the most abundant biological entities throughout marine and terrestrial ecosystems but little is known about virus–mineral interactions or the potential for virus preservation in the geological record Here we use contextual metagenomic data and microscopic analyses to show that viruses occur in high diversity within a modern lacustrine microbial mat and vastly outnumber prokaryotes and other components of the microbial mat Experimental data reveal that mineral precipitation takes place directly on free viruses and Viruses are initially permineralized by amorphous magnesium silicates which then alter to magnesium carbonate nanospheres of ~80–200 nm in diameter during diagenesis Our findings open up the possibility to investigate the evolution and geological history of viruses and their role in organomineralization as well as providing an alternative explanation for enigmatic carbonate nanospheres previously observed in the geological record The data presented here are obtained from living mats collected from the natural lake setting (NLS) and from simulated diagenetic experiments (SDEs) mimicking diagenetic conditions at the water–sediment interface These experiments allowed us to trace the changes in abundance and morphology of viruses and their hosts both in their living state and after their mineralization which is essential if such biosignatures are to be recognized in the geological record The total number of viral strains belonging to a specific order is shown on the right; when no specific order was identified viral strains were grouped as ‘unassigned.’ Identified viral families are shown on the left with the number of strains in each family as a percentage of the total number of strains per each order Empty cells were mineralized and displayed more crystalline parts (dashed arrow) Some virus-like particles remained non-mineralized (black arrow) (a) Carbonate-mineralized nanospheres (for example white arrows) located in the mineral layers before HF–HCl acid digestion (b) Some nanospheres display a hexagonal shape (arrows) (a) NanoSIMS ion maps of identical analysis areas show one-to-one correlation between organic material (12C14N−) and silicate mineral phases (16O− and 28Si−) (b) TEM image shows virus morphology and exact correlation to the boxed portion of the NanoSIMS chemical maps Circled viruses are the same in all images (and enlarged in the boxed TEM image) A second possible rounded virus (arrow) likely corresponds to a more advanced stage in the mineralization process because of its larger size and therefore might logically be expected to be the main drivers of organomineralisation in this environment are crucially important in nucleation processes that control the mineralization of microbial mats Viruses may have been instrumental in promoting the evolution of early microbial ecosystems on Earth This is particularly pertinent here given that viruses are so abundant within a microbial mat one of Earth’s most primitive and enduring ecosystems but the new findings reported in this study opens up the potential to identify viruses in the geological record and understand more about their geological and evolutionary history thereby suggesting a progressive Ca incorporation into metastable amMg-Si phases before conversion to stable Mg-carbonates samples were fixed in 2% glutaraldehyde in 0.1 M cacodylate buffer (CB) at pH 7.4 and at room temperature for 1 hour and postfixed in 1% osmium tetroxide in CB for one hour at room temperature the material was embedded in 2.5% agarose and dehydrated before inclusion in Epon resin Sections (70 nm for electron microscopy) were cut on a Leica ultramicrotome using a diamond knife (Diatome) Sections for electron microscopy were transferred onto carbon-coated films on copper grids or onto single slot grids coated with Formvar films Ultrathin sections were stained for 10 min in 1% uranyl acetate in water TEM observations were performed with a Phillips CM100 transmission electron microscope (Paris-Sud University and Zurich University) and Phillips CM120 (Claude Bernard Lyon 1 University) Elemental analyses were performed using EDAX genesis 4000 on a CM120 STEM (University of Zurich) Microbial mat samples were fixed in 2% glutaraldehyde then platinum coated before imaging with a Jeol JSM 6400 SEM Images were acquired at a resolution of 256 × 256 pixels by rastering the beam over an area of 6 × 6 μm The relatively short dwell time ensured that the delicate ultrathin sections were not destroyed by the ion beam The sections would typically ‘burn through’ after two or three images were acquired it was not possible to collect data using both the Cs+ and O− ion sources on the same sections meaning that the distribution of cations such as Ca and Mg could not be mapped from the same sections as 16O− The data were corrected for a detector dead-time of 44 ns on the individual pixels 10% SDS and proteinase K before incubation at 56 °C for one hour Viral DNA was purified through two subsequent phenol–chloroform treatment steps followed by isopropanol precipitation replicate samples of viral DNA (n=3) were amplified by GenomiPhi V2 kit (GE Healthcare) and pooled together Pooled replicates were purified using Wizard PCR and Gel Clean-up kit (Promega) potential contamination due to prokaryotic and eukaryotic DNA was checked in the viral DNA sample by PCR targeting 16S and 18S rRNA genes and gel electrophoresis analysis After having ruled out the presence of contaminating prokaryotic or eukaryotic DNA the sample was sequenced using a 454 FLX Titanium platform (Macrogen Inc. Sample processing for metagenomic analyses of viral DNA was performed by the Microbial and Molecular Ecology laboratory of the Polytechnic University of Marche comparing reads against the RefSeq database with an E-value threshold of 10−5 and normalizing the results for the genome length of each taxon Taxonomic affiliations and average viral genome size were computed and automated phylogenies for specific marker genes and viral families were constructed we counted the number of identified viral strains instead of the sequences affiliated to them affiliation of viruses to families and nucleic acid structure were determined in this way When such affiliations were not possible to ascertain strains were collected into the respective ‘unassigned’ groups Viruses as new agents of organomineralization in the geological record Accession codes: Metagenomic data have been deposited in the Metavir database (http://metavir-meb.univ-bpclermont.fr/) under Project name ‘Lagoa Vermelha’ Photosynthetic microbial mats in the 3.416-Myr-old ocean A new window into Early Archean life: microbial mats in Earth’s oldest siliciclastic tidal deposits (3.2 Ga Moodies Group Abiological origin of described stromatolites older than 3.2 Ga Fossil and Recent Biofilms: A Natural History of the Impact of Life on Planet Earth 482Kluwer Scientific Publishers: Dordrecht Defining biominerals and organominerals: direct and indirect indicators of life Processes of carbonate precipitation in microbial mats Microbial carbonates: the geological record of calcified bacterial-algal mats and biofilms Biodiversity and biogeography of phages in modern stromatolites and thrombolites Sulfate-reducing bacteria induce low-temperature Ca–dolomite and high Mg–calcite formation in:Manual Aquatic Viral Ecology eds Wilhelm S 182–192Manual of Aquatic Viral Ecology: ASLO Mg-silica precipitation in fossilization mechanisms of sand tufa endolithic microbial community Microbialite formation in seawater of increased alkalinity Going nano: a new step toward understanding the processes governing freshwater ooid formation Applied and theoretical aspects of virus adsorption to surfaces Adsorption and precipitation of iron from seawater on a marine bacteriophage (PWH3A-P1) Virus mineralization at low pH in the Rio Tinto Marine viruses and their biogeochemical and ecological effects Aerobic microbial dolomite at the nanometer scale: implications for the geologic record SEM imaging of bacteria and nannobacteria in carbonate sediments and rocks A structural comparison of bacterial microfossils vs Nanoscale study of As biomineralization in an acid mine drainage system Nanoscale detection of organic signatures in carbonate microbialites Marine viruses—major players in the global ecosystem Major viral impact on the functioning of benthic deep-sea ecosystems Microbial Mats in Sandy Deposits from the Archean era to today 194Springer (2010) A fresh look at the fossil evidence for early Archaean cellular life in:Environmental Electrochemistry: Analyses of Trace Element Biogeochemistry Determination of viral production in aquatic sediments using the dilution-based approach Prokaryote diversity and viral production in deep-sea sediments and seamounts Focussing of a transient low energy Cs+ probe for improved NanoSIMS characterizations Cold Spring Harbor Laboratory Cold Spring Harbor (1989) Laboratory procedures to generate viral metagenomes The metagenomics RAST server—a public resource for the automatic phylogenetic and functional analysis of metagenomes Metavir: a web server dedicated to virome analysis The GAAS metagenomic tool and its estimations of viral and microbial average genome size in four major biomes Diverse circovirus-like genome architectures revealed by environmental metagenomics Download references This study was supported by the Swiss National Science Foundation (grant 200020_127327) the European Science Foundation (Archean Program) and Project PETHROS Petrobras E&P We acknowledge Hans-Peter Gautschi for his assistance with EDAX Paris-Sud and the Centre technologique des microstructures scientific and technical assistance of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy was financially supported by the National Projects EXPLODIVE (FIRB 2008 was supported by the RITMARE (Ricerca Italiana in Mare) coordinated by the Italian National Research Council (CNR) funded by MIUR was supported by an Australian Research Council grant to the Centre of Excellence for Core to Crust Fluid Systems Australian Research Council Centre of Excellence for Core to Crust Fluid Systems & Centre for Exploration Targeting Department of Life and Environmental Sciences Michael Tangherlini & Roberto Danovaro conducted SEM and TEM analyses and wrote the article molecular and metagenomic analyses and contributed to writing the article processed the data and helped to write the manuscript All authors edited and commented on the manuscript The 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Microbiological Chemistry and Geomicrobiology Volume 11 - 2020 | https://doi.org/10.3389/fmicb.2020.00948 Modern stromatolites are key to the record of past microbial activity preserved in fossil carbonate deposits Mono-phototrophic cultures dominated by the cyanobacterium Geitlerinema sp were obtained from a laboratory-maintained low magnesium-calcite stromatolite originating from Lagoa Vermelha This lagoonal system has been described as a Precambrian analog illustrating a period of photosynthetically induced atmospheric oxygenation which created a global sanctuary from shortwave solar radiation and enabled the evolution of modern life on Earth The enrichment cultures precipitate carbonates in minimal media suggesting that cyanobacterial photosynthesis and extracellular polymeric substance production may be crucial in the mineralization of the studied stromatolite can build and maintain filamentous mats under long-term UV-C exposure Our results suggest that present day stromatolites dominated by cyanobacteria may be interpreted as biosignatures of atmospheric oxygenation and have implications for the search for putative biological traces on Mars This renders them key players contributing majorly to carbonate deposition in modern lithifying mats A stromatolitic record of oxygenic cyanobacterial photosynthesis may therefore be key to terraforming approaches as well The microbial mats of Lagoa Vermelha and other modern stromatolites are essential to understand the biotic mechanisms of carbonate deposition in past systems we analyze the microbial community composition by 16S rRNA gene amplicon sequencing and carbonate deposition using stable C and O isotope analysis Additional experiments were performed with Geitlerinema sp enrichments to test their ability to mineralize carbonate and grow under long-term UV-C radiation The studied stromatolite has been kept at room temperature in a hypersaline (>7% salt) aquarium at ETH Zurich, Switzerland, and currently at the Vrije Universiteit in Amsterdam, the Netherlands, for a total period of 15 years. An approximately 0.5 cm deep, 3 cm tall and 7 cm wide slice of the microbial mat was cut from the stromatolite (Figure 1) The biofilm covering the top layer was carefully removed to avoid potential contamination with non-associated algae The slice was subdivided into smaller pieces according to the intended use and stored in saline solution if not immediately processed An initial assessment of the nature of the phototrophic community was performed by fluorescence microscopy to distinguish between Chlorophyll a containing micro-eukaryotic alga and phycoerythrin containing cyanobacteria Chlorophyll a was visualized using the Carl Zeiss Filter Set 09 (excitation 450–490 nm emission 515 nm) and phycoerythrin was visualized using the Carl Zeiss Filter Set 20 (excitation 546 nm Cross section of the studied stromatolite illustrating the layered microbial mat which embeds the crystalline layer of unconsolidated precipitates and relevant zones of the carbonate deposit below The top green layer generally features photosynthetic cyanobacteria producing primary OM to be consumed by aerobic heterotrophic bacteria in the uppermost part of the layer below The diverse community of this zone moreover comprises autotrophs especially the purple sulfur bacteria which give the layer its characteristic pink color and are capable of microaerophilic or anoxygenic photosynthesis in the deeper parts of the zone Below the distinct layer of unconsolidated precipitates composed of carbonate minerals such as magnesium calcite and/or dolomite the community is dominated by strictly anoxic conditions and salvages (in-)organic metabolic products of the upper layers in association with less pronounced crystal deposits The most prominent process in this black layer is sulfate reduction next to obligate fermentation and other anoxygenic heterotrophy The carbonate deposit in the lower half of the stromatolite comprises granulated as well as more compact strata toward the bottom OTU abundances were normalized to relative abundance in percentage The sequencing data is deposited in the NCBI small read archive and listed under BioProject ID PRJNA610984 soaked in ultrapure water for 2 days and subsequently dried in an oven at 40°C Isotope δ13C and δ18O values were established in relation to the Vienna Pee Dee Belemnite (VPDB) standard on a Finnigan MAT253 mass spectrometer using the Gasbench II Sample size was corrected using the Vrije Universiteit Amsterdam in house carbonate standard (VICS) while the international IAEA-603 was measured as a control standard The long-term standard deviation of the routinely analyzed in-house standard is <0.1‰ (1σ) for both carbon and oxygen isotope ratios Isotopic values were established in four samples per layer A sterile microscope slide was added to provide a retrievable surface for cellular growth and carbonate nucleation The liquid cultures were incubated aerobically at 30°C and exposed to artificial illumination (40 W LED at 40 cm distance) in a 12 h light/12 h dark rhythm Cell material was scraped from ASN-III-CS agar grown cultures for molecular analysis 16S amplicon sequencing and taxonomic assignment were performed as described above the pellet was washed with ultrapure water by centrifuging three times at 8,000 × g and resuspended in 200 μl of ultrapure water All samples were treated ultra-sonically in a bath sonicator for 60 s 5 μl of dispersion were pipetted on a glow discharged TEM-grid for analysis on a FEI Talos F200X TEM Material from solid cultures was examined in TEM bright field mode while liquid cultures were additionally analyzed in STEM dark field mode and tilted between 30° and 60° if applicable EDS was conducted to assess the elemental composition of sample compounds and ED to assign a crystalline or amorphous character carbonate crusts from solid cultures were subjected to stable isotope analysis Sample preparation and determination of δ13C and δ18O values was performed as described above Free-floating cell material from liquid ASN-III-CL cultures was transferred to sterile saline solution which was used as inoculum for glass beakers containing solid ASN-III-US or liquid ASN-III-UL medium (Supplementary Table S1) The beakers were covered in a plastic wrap punctured with a fine needle to allow gas exchange A sterile microscope slide was added to the liquid cultures as retrievable surface for cellular growth Both solid (n = 5) and liquid (n = 5) cultures plus a negative control without bacterial cells each were placed in a laminar flow chamber beneath a UV-C tube (15 W peak at 250 nm) mounted at 40 cm distance from the surface of the culture medium The cultures were subjected to 12 h of both continuous UV-C and photosynthetically active radiation (PAR) combined (40 W LED To avoid natural light exposure throughout the day the chamber was completely covered in tinfoil consisting of five solid and five liquid cultures with cells and one solid and one liquid culture without bacterial cells was placed in an opaque box and exposed to PAR exclusively for 12 h light/12 h dark Four weeks after the start of the experiment one of the positive agar controls was added to the UV-C exposed experiment to monitor UVR effect on intact cyanobacterial mats In response to the appearance of red precipitate in the liquid UVR-exposed experiments negative controls of ASN-III-UL medium and sterile demineralized water covered in non-punctured plastic wrap were added to examine external contamination Samples of red precipitate from a culture experiment were centrifuged at 10,000 × g for 90 s The pellet was washed three times in ultrapure water and resuspended in 200 μl The material was further prepared for TEM-EDS as described above before being examined in TEM bright field mode for imaging and with an EDS detector for elemental analysis Cyanobacterial mat cover was monitored over a period of 6 weeks in all cultures Organic material (OM) was prepared for and assessed via TEM-EDS and ED as described above Evenness was overall low with the two dominant archaeal OTUs OTU_17 and OTU_29 making up 78% of the total community abundance The Crystal layer is dominated by OTU_17 and OTU_13 assigned to the orders Methanosarcinales and Halobacteriales and the black layer is dominated by OTU_29 and OTU_25 assigned to the classes Lokiarchaeia and Bathyarchaeia Taxonomic composition of microbial mat layers showing (A) archaeal read counts and (B) bacterial read counts The relative phyla frequency within a layer is indicated in percent if respective read counts constitute >5% Diversity estimators for the bacterial community revealed a slight increase in Chao-1 richness from 96 to 135 from the top to the bottom layer (Supplementary Table S2) Shannon diversity index varied little between the three top layers and was highest in the bottom layer (H = 3.22) The evenness was overall low (0.13–0.20) indicative for a relative low number of dominant species Indeed the 14 most abundant OTUs make up more than 75% of the total abundance The archaeal community in the top three layers mainly consists of Euryarchaeota (>90% of total abundance) These layers are dominated by methanogens of the genus Methanohalophilus and to a lesser extent of Halobacteria The Halobacteria contribution is highest in the third layer (∼13%) but they form less than 0.3% of the archaeal population in the bottom layer The black bottom layer is dominated by phylum Asgardarchaeota class Lokiarchaeota (76% of total) that are neglectable in the other layers The bottom layer furthermore contains uncultured members of the orders Bathyarchaeia (∼12%) and Thermoplasmata (∼11% - Marine Benthic Group D) SEM-EDS of the crystalline layer embedded in the stromatolitic microbial mat (B) EDS of spheroids (light blue arrows) adhered to sheaths of EPS (dark blue arrows) and (D) granulated texture of crystalline microstructures and EPS Mean isotope delta values throughout the layer of crystalline precipitates in the mat (Top 0) and the primary (Top 1) and bottom (Top 4) layer of the carbonate deposit the bacterial cover started to die off on the increasingly desiccated agar base Molecular analysis identified the cyanobacterium as Geitlerinema sp and the cultures as non-axenic containing also members of Bacteroidetes (averaging 15%) and Proteobacteria (averaging 12%) Since molecular analysis identified no other cyanobacteria in the enrichment cultures Morphology of isolates from mixed agar culture under an optical microscope in standard adjustment (smaller pictures) and equipped with a green filter (big picture) The EPS appears as white to yellowish sheaths around the cyanobacterial cells The mean δ18O of carbonate crusts resulted in 0.39‰ VPDB while the average isotopic ratio of stable carbon isotopes had a value of −12.26‰ VPDB Crystal nucleation and growth observed under an optical microscope (A) Nucleation of globules in association with bacterial filaments and development of darker spots (indicated with arrows) in the medium (B) increased number of nucleating crystals around filaments attracted to a CO2 or O2 bubble in the medium (C) amalgamation of globules into granulated textures growing into (D) larger crystals on the surface of filament clusters and eventually (E) into carbonate crusts visible to the naked eye SEM imaging and EDS analysis of carbonate crusts from agar cultures illustrating (A) needle morphology (B) aggregate texture including nucleating spheroids (light blue arrows) in EPS sheaths (dark blue arrows) and (C) sheaths of EPS with nucleating spheroids as well as a calcified cell (white arrow) associated with spheroids on the far left and (D) indexed ED patterns of calcite sample compounds Intracellular inclusions from liquid culture experiments (A) Distribution of inclusions within the cells and throughout a filament visualized in HAADF mode (B) Map and exemplary ED of intracellular granules (A) Growth in control series and UVR-exposed experiments after 6 weeks distinguished in solid (S) and liquid (L) cultures including negative controls (NC) Cultures featuring bacterial growth are marked with a green dot continuously sterile cultures with a red dot precipitation of red flakes could be observed (see also B) (B) Cyanobacterial growth occurred exclusively beneath the microscope slide in liquid culture subjected to UV-C and on only top of the slide in the control (C) Development of an intact cyanobacterial mat in agar culture after exposure to UVR Intracellular inclusions from the UVR experiment (A) Map of a filament from liquid culture exposed to UVR surrounded by the Fe and Mn rich precipitated flakes (B) Map of a filament from an agar control culture (C) Representative EDS of the intracellular inclusions (D) Representative ED of the intracellular inclusions (E) Distribution of inclusions throughout the filaments and cells visualized in HAADF mode The overall dominant genera are mainly anaerobic or microaerophilic heterotrophic bacteria, such as Balneolaceae_g, Marinobacter (facultative aerobe heterotrophs) and Marinospirillum (micro-aerophilic heterotroph) (Supplementary Table S4). Those genera may be involved in lamination formation requiring anoxic conditions and EPS nucleation sites (Vasconcelos et al., 2006) a combination of both heterotrophy and operating carbon concentrating mechanisms (CCM) may lead to precipitation and diagenesis of carbonate with a more negative δ13C than material mediated through regular C3 photosynthesis The near zero δ18O values throughout the layers indicate an approximate equilibrium of precipitated and lithified carbonates with the aquatic environment as well as a relatively similar isotopic composition of the Lagoa Vermelha natural seawater and the laboratory saline solution (including minor fluctuations) when comparing unconsolidated precipitates to the mature deposit Culture growth on agar indicates a general adaption to the periodically semi-arid conditions with direct air exposure common in Lagoa Vermelha with the gelatinous agar itself simulating a mat-like substrate Mg2+ ions are generally present in significantly hydrated form and react slower than Ca2+ ions making them less bioavailable and presumably requiring even higher initial concentrations than introduced in order to balance the disparity Spheroids amalgamate in later stages and form calcite in different textures giving distinct electron diffraction signals but featuring an overall rather poorly crystallized character which indicates nutrient limitation in the aged liquid medium The PolyP inclusions may represent another stable adaption of the cultured Geitlerinema to the dynamic conditions in Lagoa Vermelha facilitating long-term mat survival and stromatolite growth chemical and isotopic characteristics of the extracellular carbonate deposits document the mineralization of carbonates similar to the primary precipitates of the laboratory-incubated stromatolite and in the mono-phototrophic culture and represent an important precondition for the interpretation of in situ precipitated fossil stromatolites The readily adsorbance of metal ions by bacteriogenic MnO2 might render its presence especially meaningful for carbonate depositing systems but further analysis of the composition of manganese-rich flakes precipitated by UV-C irradiation would be needed to gain insight into this process The highly energetic effect of the shortwave UV radiation did not allow bacterial growth on agar, as opposed to the liquid medium where cultivation of few mats could be observed (Figure 8A). In accordance with both cultivation experiment results and the significantly shortened time frame, this involved lack of extracellular precipitation but formation or maintenance of PolyP granules presumably facilitating stress acclimation (Figure 9) A metabolically diverse community accounts for precipitation and diagenesis of magnesium calcite on a laboratory-controlled stromatolite is the major cyanobacterial primary producer in this system and responsible for the oxygenation of the top layer The Geitlerinema enrichment was shown to facilitate carbonate precipitation and was able to endure long-term exposure to highly energetic UV-C radiation The unexpected large number of yet uncultivated Archaea related to the Asgard group may allow us to study this newly identified phylum and facilitate their cultivation and investigation while the abiotic precipitation of putative manganese oxides via high-energy solar radiation might be of interest regarding the geochemical cycles of pre-GOE systems this study will further contribute to our search for putative extraterrestrial live and especially fossilized biota as well as potential oxygenation of the presently UV-C permeable atmosphere on Mars The raw data supporting the conclusions of this article will be made available by the authors The sequencing data has been submitted to the NCBI-SRA database under BioProject ID PRJNA610984 MS-R performed conception and design of the study assessed results and advised in practical execution and assessed results as an internship part of the MSc track Freshwater and Marine Biology and also wrote the draft of the manuscript HB performed both practical and analytical taxonomic assessment and contributed substantially to the writing and development of the manuscript reviser and to the development of the manuscript All authors contributed to manuscript revision This research was funded by the Origins Center project 190438131 of the Dutch Research Council (NWO) and National Research 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This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) *Correspondence: Mónica Sánchez-Román, bS5zYW5jaGV6cm9tYW5AdnUubmw=; c2FuY2hlenJvbWFubW9uaWNhQGdtYWlsLmNvbQ== Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher 94% of researchers rate our articles as excellent or goodLearn more about the work of our research integrity team to safeguard the quality of each article we publish na 2ª edição do Diário Oficial do Estado (DOE) de terça-feira (21/5) que atualiza a lista de municípios em estado de calamidade pública e em situação de emergência a medida foi tomada a partir de requerimentos e novas informações trazidas pelos municípios sobre as áreas afetadas e sobre a extensão dos danos ocorridos Também foi motivada pela ampliação do acesso pelo Estado ampliando as informações sobre as consequências do evento meteorológico registrado entre o fim de abril e o início de maio no Rio Grande do Sul Além da reclassificação da intensidade do desastre também houve a inclusão de municípios na declaração estadual foram identificados 46 municípios em estado de calamidade e 320 em situação de emergência o Decreto 57.626 entra em vigor na data da publicação (21/5) retroagindo seus efeitos a 13 de maio de 2024