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Despite the extent use of geochemical tracers to track warm air mass origin reaching the Antarctic continent, we present here evidences that microorganisms being transported by the atmosphere and deposited in fresh snow layers of Antarctic ice sheets do act as tracers of air mass advection from the Southern Patagonia region to Northern Antarctic Peninsula. We combined atmospheric circulation data with microorganism content in snow/firn samples collected in two sites of the Antarctic Peninsula (King George Island/Wanda glacier and Detroit Plateau) by using flow cytometer quantification. In addition, we cultivated, isolated and submitted samples to molecular sequencing to precise species classification. Viable gram-positive bacteria were found and recovered in different snow/firn layers samples, among dead and living cells, their number concentration was compared to northern wind component, stable isotopes of oxygen, d18O, and the concentration of crustal elements (Fe, Ti and Ca). Use of satellite images combined with air mass back-trajectory analysis obtained from the NOAA/ HYSPLIT model corroborated the results.
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Bactérias , Vento , Regiões AntárticasRESUMO
Microorganisms in Antarctica are recognized for having crucial roles in ecosystems functioning and biogeochemical cycles. To explore the diversity and composition of microbial communities through different terrestrial and marine Antarctic habitats, we analyze 16S rRNA sequence datasets from fumarole and marine sediments, soil, snow and seawater environments. We obtained measures of alpha- and beta-diversities, as well as we have identified the core microbiome and the indicator microbial taxa of a particular habitat. Our results showed a unique microbial community structure according to each habitat, including specific taxa composing each microbiome. Marine sediments harbored the highest microbial diversity among the analyzed habitats. In the fumarole sediments, the core microbiome was composed mainly of thermophiles and hyperthermophilic Archaea, while in the majority of soil samples Archaea was absent. In the seawater samples, the core microbiome was mainly composed by cultured and uncultured orders usually identified on Antarctic pelagic ecosystems. Snow samples exhibited common taxa previously described for habitats of the Antarctic Peninsula, which suggests long-distance dispersal processes occurring from the Peninsula to the Continent. This study contributes as a baseline for further efforts on evaluating the microbial responses to environmental conditions and future changes.
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Bactérias , Microbiota , Bactérias/genética , Regiões Antárticas , RNA Ribossômico 16S/genética , Archaea/genética , Microbiota/genética , SoloRESUMO
Continental slopes can play a significant contribution to marine productivity and carbon cycling. These regions can harbour distinct geological features, such as salt diapirs and pockmarks, in which their depressions may serve as natural sediment traps where different compounds can accumulate. We investigated the prokaryotic communities in surface (0-2 cm) and subsurface (18-20 or 22-24 cm) sediments from a salt diapir and pockmark field in Santos Basin, Southwest Atlantic Ocean. Metabarcoding of 16 samples revealed that surface sediments were dominated by the archaeal class Nitrososphaeria, while the bacterial class Dehalococcoidia was the most prevalent in subsurface samples. Sediment strata were found to be a significant factor explaining 27% of the variability in community composition. However, no significant difference was observed among geomorphological features. We also performed a metagenomic analysis of three surface samples and analysed the highest quality metagenome-assembled genome retrieved, which belonged to the family CSP1-5, phylum Methylomirabilota. This non-methanotrophic methylotroph contains genes encoding for methanol oxidation and Calvin Cycle pathways, along with diverse functions that may contribute to its adaptation to deep-sea habitats and to oscillating environmental conditions. By integrating metabarcoding and metagenomic approaches, we reported that CSP1-5 is prevalent in the sediment samples from Santos Basin slope, indicating the potential importance of methanol metabolism in this region. Finally, using a phylogenetic approach integrating 16S rRNA sequences assigned to Methylomirabilota in this study with those from a public database, we argued that CSP1-5 public sequences might be misclassified as Methylomirabilaceae (the methanotrophic clade) and, therefore, the role of these organisms and the methanol cycling could also be neglected in other environments.
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Sedimentos Geológicos , Metanol , Metanol/metabolismo , Sedimentos Geológicos/microbiologia , Filogenia , RNA Ribossômico 16S/genética , RNA Ribossômico 16S/metabolismo , Células Procarióticas , Bactérias , ArchaeaRESUMO
Microbial communities play a key role in the ocean, acting as primary producers, nutrient recyclers, and energy providers. The São Paulo Plateau is a region located on the southeastern coast of Brazil within economic importance, due to its oil and gas reservoirs. With this focus, this study examined the diversity and composition of microbial communities in marine sediments located at three oceanographic stations in the southern region of São Paulo Plateau using the HOV Shinkai 6500 in 2013. The 16S rRNA gene was sequenced using the universal primers (515F and 926R) by the Illumina Miseq platform. The taxonomic compositions of samples recovered from SP3 station were markedly distinct from those obtained from SP1 and SP2. Although all three stations exhibited a high abundance of Gammaproteobacteria (> 15%), this taxon dominated more than 90% of composition of the A and C sediment layers at SP3. The highest abundance of the archaeal class Nitrososphaeria was presented at SP1, mainly at layer C (~ 21%), being absent at SP3 station. The prediction of chemoheterotrophy and fermentation as important microbial functions was supported by the data. Additionally, other metabolic pathways related to the cycles of nitrogen, carbon and sulfur were also predicted. The core microbiome analysis comprised only two ASVs. Our study contributes to a better understanding of microbial communities in an economically important little-explored region. This is the third microbiological survey in plateau sediments and the first focused on the southern region.
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Sedimentos Geológicos , Microbiota , Sedimentos Geológicos/microbiologia , RNA Ribossômico 16S/genética , Brasil , Archaea/genética , Microbiota/genética , Oceano AtlânticoRESUMO
Mining of deep-sea Fe-Mn deposits will remove crusts and nodules from the seafloor. The growth of these minerals takes millions of years, yet little is known about their microbiome. Besides being key elements of the biogeochemical cycles and essential links of food and energy to deep-sea, microbes have been identified to affect manganese oxide formation. In this study, we determined the composition and diversity of Bacteria and Archaea in deep-sea Fe-Mn crusts, nodules, and associated sediments from two areas in the Atlantic Ocean, the Tropic Seamount and the Rio Grande Rise. Samples were collected using ROV and dredge in 2016 and 2018 oceanographic campaigns, and the 16S rRNA gene was sequenced using Illumina platform. Additionally, we compared our results with microbiome data of Fe-Mn crusts, nodules, and sediments from Clarion-Clipperton Zone and Takuyo-Daigo Seamount in the Pacific Ocean. We found that Atlantic seamounts harbor an unusual and unknown Fe-Mn deposit microbiome with lower diversity and richness compared to Pacific areas. Crusts and nodules from Atlantic seamounts have unique taxa (Alteromonadales, Nitrospira, and Magnetospiraceae) and a higher abundance of potential metal-cycling bacteria, such as Betaproteobacteriales and Pseudomonadales. The microbial beta-diversity from Atlantic seamounts was clearly grouped into microhabitats according to sediments, crusts, nodules, and geochemistry. Despite the time scale of million years for these deposits to grow, a combination of environmental settings played a significant role in shaping the microbiome of crusts and nodules. Our results suggest that microbes of Fe-Mn deposits are key in biogeochemical reactions in deep-sea ecosystems. These findings demonstrate the importance of microbial community analysis in environmental baseline studies for areas within the potential of deep-sea mining.
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Sedimentos Geológicos , Microbiota , Archaea , Bactérias , Sedimentos Geológicos/química , Oceano Pacífico , RNA Ribossômico 16S/genéticaRESUMO
Antarctic active volcanoes can disperse pyroclastic minerals at long distances, transporting nutrients and microorganisms to the surrounding glacial environment. The sedimented volcanic materials - called tephras - may interact with glacier ice and produce a unique environment for microbial life. This study aimed to describe the microbial community structure of an Antarctic glacier ice with tephra layers in terms of its taxonomic and functional diversity. Ice samples from Collins Glacier (King George Island) containing tephra layers of Deception Island volcano were analyzed by a whole shotgun metagenomic approach. Taxonomic analysis revealed a highly diverse community dominated by phyla Bacteroidetes, Cyanobacteria and Proteobacteria. The dominant genera were Chitinophaga (13%), Acidobacterium (8%), and Cyanothece (4%), being all of these known to include psychrotolerant and psychrophilic strains. Functional diversity analysis revealed almost complete carbon, nitrogen and sulfur biogeochemical cycles. Carbohydrate metabolism of the ice-tephra community uses both organic and inorganic carbon inputs, where photosynthesis plays an important role through CO2 fixation. Our results also demonstrate a biotechnological potential for this glacial community, with functional annotations for styrene degradation and carotenoid pigment genes. Future metatranscriptomic studies shall further reveal the active strategies and the biotechnology potential of extremophiles from this unique ice-tephra microbial community.
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Cianobactérias , Microbiota , Regiões Antárticas , Carbono , Microbiota/genética , RNA Ribossômico 16S/genéticaRESUMO
Microbial communities have been explored in various terrestrial subsurface ecosystems, showing metabolic potentials that could generate noteworthy morphological and molecular biosignatures. Recent advancements in bioinformatic tools have allowed for descriptions of novel and yet-to-be cultivated microbial lineages in different ecosystems due to the genome reconstruction approach from metagenomic data. Using shotgun metagenomic data, we obtained metagenome-assembled genomes related to cultivated and yet-to-be cultivated prokaryotic lineages from a silica and iron-rich cave (Monte Cristo) in Minas Gerais State, Brazil. The Monte Cristo Cave has been shown to possess a high diversity of genes involved with different biogeochemical cycles, including reductive and oxidative pathways related to carbon, sulfur, nitrogen, and iron. Three genomes were selected for pangenomic analysis, assigned as Truepera sp., Ca. Methylomirabilis sp., and Ca. Koribacter sp. based on their lifestyles (radiation resistance, anaerobic methane oxidation, and potential iron oxidation). These bacteria exhibit genes involved with multiple DNA repair strategies, starvation, and stress response. Because these groups have few reference genomes deposited in databases, our study adds important genomic information about these lineages. The combination of techniques applied in this study allowed us to unveil the potential relationships between microbial genomes and their ecological processes with the cave mineralogy and highlight the lineages involved with anaerobic methane oxidation, iron oxidation, and radiation resistance as functional models for the search for extant life-forms outside our planet in silica- and iron-rich environments and potentially on Mars.
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Metagenoma , Microbiota , Brasil , Cavernas/microbiologia , Metagenômica , Microbiota/genética , FilogeniaRESUMO
Deep-sea carbonate mounds can harbor a wide variety of heterotrophic and chemosynthetic microbial communities, providing biodiversity hotspots among the deep-sea benthic ecosystems. This study examined the bacterial and archaeal diversity and community structure in the water column and sediments associated with a recently described giant carbonate mound named Alpha Crucis Carbonate Ridge (ACCR), located in the Southwestern Atlantic Ocean. Because of the acoustic evidence of gas chimneys from a previous study, we further evaluated the chemosynthetic primary production through in situ-simulated dark carbon fixation rates. Pelagic microbial communities varied significantly with depth, showing a high abundance of photosynthetic groups in surface waters and taxa related to nitrification in intermediate and deep waters. The benthic communities from the top of the ACCR were very similar along with the sediment depth, while those from the base of the ACCR showed a clear stratification pattern, with members in the deep strata mainly related to anoxic and chemosynthetic ecosystems. Dark carbon fixation rates were of the same order of magnitude as those of deep-sea cold seeps and hydrothermal vents. Our study provides the first description of the ACCR microbiome and adds new information to help formulate and implement future conservation and management strategies for vulnerable marine ecosystems.
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Fontes Hidrotermais , Microbiota , Archaea/genética , Oceano Atlântico , Biodiversidade , Carbonatos , EcossistemaRESUMO
Active volcanoes in Antarctica have remarkable temperature and geochemical gradients that could select for a wide variety of microbial adaptive mechanisms and metabolic pathways. Deception Island is a stratovolcano flooded by the sea, resulting in contrasting ecosystems such as permanent glaciers and active fumaroles, which creates steep gradients that have been shown to affect microbial diversity. In this study, we used shotgun metagenomics and metagenome-assembled genomes to explore the metabolic potentials and survival strategies of microbial communities along an extreme temperature gradient in fumarole and glacier sediments on Deception Island. We observed that communities from a 98 °C fumarole were significantly enriched in genes related to hyperthermophilic (e.g. reverse gyrase, GroEL/GroES and thermosome) and oxidative stress responses, as well as genes related to sulfate reduction, ammonification and carbon fixation. Communities from <80 °C fumaroles possessed more genes related osmotic, cold- and heat-shock responses, and diverse metabolic potentials, such as those related to sulfur oxidation and denitrification, while glacier communities showed abundant metabolic potentials mainly related to heterotrophy. Through the reconstruction of genomes, we were able to reveal the metabolic potentials and different survival strategies of underrepresented taxonomic groups, especially those related to Nanoarchaeota, Pyrodictiaceae and thermophilic ammonia-oxidizing archaeal lineages.
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Bactérias , Microbiota , Regiões Antárticas , Archaea/genética , Bactérias/genética , Microbiota/genética , TemperaturaRESUMO
Marine plastic pollution is a global concern because of continuous release into the oceans over the last several decades. Although recent studies have made efforts to characterize the so-called plastisphere, or microbial community inhabiting plastic substrates, it is not clear whether the plastisphere is defined as a core community or as a random attachment of microbial cells. Likewise, little is known about the influence of the deep-sea environment on the plastisphere. In our experimental study, we evaluated the microbial colonization on polypropylene pellets and two types of plastic bags: regular high density polyethylene (HDPE) and HDPE with the oxo-biodegradable additive BDA. Gravel was used as control. Samples were deployed at three sites at 3300 m depth in the Southwest Atlantic Ocean and left for microbial colonization for 719 days. For microbial communities analysis, DNA was extracted from the biofilm on plastic and gravel substrates, and then the 16S rRNA was sequenced through the Illumina Miseq platform. Cultivation was performed to isolate strains from the plastic and gravel substrates. Substrate type strongly influenced the microbial composition and structure, while no difference between sites was detected. Although several taxa were shared among plastics, we observed some groups specific for each plastic substrate. These communities comprised taxa previously reported from both epipelagic zones and deep-sea benthic ecosystems. The core microbiome (microbial taxa shared by all plastic substrates) was exclusively composed by low abundance taxa, with some members well-described in the plastisphere and with known plastic-degradation capabilities. Additionally, we obtained bacterial strains that have been previously reported inhabiting plastic substrates and/or degrading hydrocarbon compounds, which corroborates our metabarcoding data and suggests the presence of microbial members potentially active and involved with degradation of these plastics in the deep sea.
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Microbiota , Plásticos , Archaea/genética , Oceano Atlântico , RNA Ribossômico 16SRESUMO
Seamounts are often covered with Fe and Mn oxides, known as ferromanganese (Fe-Mn) crusts. Future mining of these crusts is predicted to have significant effects on biodiversity in mined areas. Although microorganisms have been reported on Fe-Mn crusts, little is known about the role of crusts in shaping microbial communities. Here, we investigated microbial communities based on 16S rRNA gene sequences retrieved from Fe-Mn crusts, coral skeleton, calcarenite, and biofilm at crusts of the Rio Grande Rise (RGR). RGR is a prominent topographic feature in the deep southwestern Atlantic Ocean with Fe-Mn crusts. Our results revealed that crust field of the RGR harbors a usual deep-sea microbiome. No differences were observed on microbial community diversity among Fe-Mn substrates. Bacterial and archaeal groups related to oxidation of nitrogen compounds, such as Nitrospirae, Nitrospinae phyla, Candidatus Nitrosopumilus within Thaumarchaeota group, were present on those substrates. Additionally, we detected abundant assemblages belonging to methane oxidation, i.e., Methylomirabilales (NC10) and SAR324 (Deltaproteobacteria). The chemolithoautotrophs associated with ammonia-oxidizing archaea and nitrite-oxidizing bacteria potentially play an important role as primary producers in the Fe-Mn substrates from RGR. These results provide the first insights into the microbial diversity and potential ecological processes in Fe-Mn substrates from the Atlantic Ocean. This may also support draft regulations for deep-sea mining in the region.
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Archaea , Manganês , Archaea/genética , Oceano Atlântico , Sedimentos Geológicos , Ferro , Filogenia , RNA Ribossômico 16S/genéticaRESUMO
Methanotrophic bacteria can use methane as sole carbon and energy source. Its importance in the environment is related to the mitigation of methane emissions from soil and water to the atmosphere. Brazilian mangroves are highly productive, have potential to methane production, and it is inferred that methanotrophic community is of great importance for this ecosystem. The scope of this study was to investigate the functional and taxonomic diversity of methanotrophic bacteria present in the anthropogenic impacted sediments from Bertioga´s mangrove (SP, Brazil). Sediment sample was cultivated with methane and the microbiota actively involved in methane oxidation was identified by DNA-based stable isotope probing (DNA-SIP) using methane as a labeled substrate. After 4 days (96 h) of incubation and consumption of 0.7 mmol of methane, the most active microorganisms were related to methanotrophs Methylomonas and Methylobacter as well as to methylotrophic Methylotenera, indicating a possible association of these bacterial groups within a methane-derived food chain in the Bertioga mangrove. The abundance of genera Methylomonas, able to couple methane oxidation to nitrate reduction, may indicate that under low dissolved oxygen tensions, some aerobic methanotrophs could shift to intraerobic methane oxidation to avoid oxygen starvation.
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Metano , Microbiota , Brasil , DNA , Isótopos , Oxirredução , Filogenia , Microbiologia do SoloRESUMO
Here we investigated the diversity of bacterial communities from deep-sea surface sediments under influence of asphalt seeps at the Sao Paulo Plateau using next-generation sequencing method. Sampling was performed at North São Paulo Plateau using the human occupied vehicle Shinkai 6500 and her support vessel Yokosuka. The microbial diversity was studied at two surficial sediment layers (0-1 and 1-4 cm) of five samples collected in cores in water depths ranging from 2456 to 2728 m. Bacterial communities were studied through sequencing of 16S rRNA gene on the Ion Torrent platform and clustered in operational taxonomic units. We observed high diversity of bacterial sediment communities as previously described by other studies. When we considered community composition, the most abundant classes were Alphaproteobacteria (27.7%), Acidimicrobiia (20%), Gammaproteobacteria (11.3%) and Deltaproteobacteria (6.6%). Most abundant OTUs at family level were from two uncultured bacteria from Actinomarinales (5.95%) and Kiloniellaceae (3.17%). The unexpected high abundance of Alphaproteobacteria and Acidimicrobiia in our deep-sea microbial communities may be related to the presence of asphalt seep at North São Paulo Plateau, since these bacterial classes contain bacteria that possess the capability of metabolizing hydrocarbon compounds.
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Bactérias/isolamento & purificação , Sedimentos Geológicos/microbiologia , Metagenoma , Microbiota/genética , Água do Mar/microbiologia , Alphaproteobacteria/classificação , Alphaproteobacteria/genética , Alphaproteobacteria/isolamento & purificação , Bactérias/classificação , Bactérias/genética , Biodiversidade , DNA Bacteriano/genética , Deltaproteobacteria/classificação , Deltaproteobacteria/genética , Deltaproteobacteria/isolamento & purificação , Gammaproteobacteria/classificação , Gammaproteobacteria/genética , Gammaproteobacteria/isolamento & purificação , Sequenciamento de Nucleotídeos em Larga Escala/métodos , Hidrocarbonetos/metabolismo , Metagenômica/métodos , RNA Ribossômico 16S/genética , Microbiologia da ÁguaRESUMO
Polar volcanoes harbor unique conditions of extreme temperature gradients capable of selecting different types of extremophiles. Deception Island is a marine stratovolcano located at Maritime Antarctica that is notable for its pronounced temperature gradients over very short distances, reaching values up to 100 °C in the fumaroles, and subzero temperatures next to the glaciers. Due to these characteristics, Deception can be considered an interesting analogue of extraterrestrial environments. Our main goal in this study was to isolate thermophilic and psychrophilic bacteria from sediments associated with fumaroles and glaciers from two geothermal sites in Deception Island, comprising temperatures between 0 and 98 °C, and to evaluate their survivability to desiccation and UV-C radiation. Our results revealed that culturable thermophiles and psychrophiles were recovered among the extreme temperature gradient in Deception volcano, which indicates that these extremophiles remain alive even when the conditions do not comprise their growth range. The viability of culturable psychrophiles in hyperthermophilic environments is still poorly understood and our work showed the importance of future studies about their survival strategies in high temperatures. Finally, the spore-forming thermophilic isolates which we found have displayed good survival to desiccation and UV-C irradiation, which suggests their potential to be further explored in astrobiological studies.
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Camada de Gelo/microbiologia , Microbiota , Termotolerância , Erupções Vulcânicas , Regiões Antárticas , Bactérias/genética , Bactérias/isolamento & purificação , Ambientes Extremos , IlhasRESUMO
An initial multiple biogeochemical dataset was acquired from the first discovered asphalt seeps in the Brazil margin during deep-sea dive surveys in 2013 using a manned submersible. These surveys were conducted on the outer escarpment of the North São Paulo Plateau. Sediment cores taken from the submersible were processed for pore water and sediment biogeochemistry. The silica concentration, as a chemical geothermometer, showed a steep gradient in the pore water, which indicates the possibility of an active brine system operating in the seepage area. Rare earth elements were used as powerful tracers of chemical processes. Low rare earth element concentrations in both asphalt and Fe-Mn oxyhydroxide-phase sediments suggests that rare earth elements were released during the oil fractionation and biodegradation processes and further depleted under the reducing environment. The main bacterial communities of the sediment were Proteobacteria in the asphalt sites, while at non-asphalt sites, the main bacterial communities of sediment were Firmicutes. Stable carbon and nitrogen isotopes were used to determine the food sources of the heterotrophs, and results suggest that asphalt probably provides a carbon source for these benthic animals. This study may provide useful information to clarify the impact of heavy hydrocarbon seepage on the marine ecosystem.
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Active volcanoes in Antarctica contrast with their predominantly cold surroundings, resulting in environmental conditions capable of selecting for versatile and extremely diverse microbial communities. This is especially true on Deception Island, where geothermal, marine, and polar environments combine to create an extraordinary range of environmental conditions. Our main goal in this study was to understand how microbial community structure is shaped by gradients of temperature, salinity, and geochemistry in polar marine volcanoes. Thereby, we collected surface sediment samples associated with fumaroles and glaciers at two sites on Deception, with temperatures ranging from 0 to 98°C. Sequencing of the 16S rRNA gene was performed to assess the composition and diversity of Bacteria and Archaea. Our results revealed that Deception harbors a combination of taxonomic groups commonly found both in cold and geothermal environments of continental Antarctica, and also groups normally identified at deep and shallow-sea hydrothermal vents, such as hyperthermophilic archaea. We observed a clear separation in microbial community structure across environmental gradients, suggesting that microbial community structure is strongly niche driven on Deception. Bacterial community structure was significantly associated with temperature, pH, salinity, and chemical composition; in contrast, archaeal community structure was strongly associated only with temperature. Our work suggests that Deception represents a peculiar "open-air" laboratory to elucidate central questions regarding molecular adaptability, microbial evolution, and biogeography of extremophiles in polar regions.
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Uncultured microorganisms comprise most of the microbial diversity existing on our planet. Despite advances in environmental sequencing and single-cell genomics, in-depth studies about bacterial metabolism and screening of novel bioproducts can only be assessed by culturing microbes in the laboratory. Here we report uncultured, or recalcitrant, microorganisms from an Antarctic soil sample, using relatively simple methods: oligotrophic media, extended incubation periods, observation under stereo microscopy, and selection of slow-growing bacteria. We managed to isolate several rare microorganisms belonging to infrequently isolated or recently described genera, for example Lapillicoccus, Flavitalea, Quadrisphaera, Motilibacter, and Polymorphobacter. Additionally, we obtained isolates presenting 16S rRNA sequence similarity ranging from 92.08 to 94.46% with any other known cultured species, including two distinct isolates from the class Thermoleophilia, that although common in Antarctic soils (as identified by metagenomics), was never reported to be isolated from such samples. Our data indicates that simple methods are still useful for cultivating recalcitrant microorganisms, even when dealing with samples from extreme environments.
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Microorganisms dominate most Antarctic marine ecosystems, in terms of biomass and taxonomic diversity, and play crucial role in ecosystem functioning due to their high metabolic plasticity. Admiralty Bay is the largest bay on King George Island (South Shetland Islands, Antarctic Peninsula) and a combination of hydro-oceanographic characteristics (bathymetry, sea ice and glacier melting, seasonal entrance of water masses, turbidity, vertical fluxes) create conditions favoring organic carbon deposition on the seafloor and microbial activities. We sampled surface sediments from 15 sites across Admiralty Bay (100-502 m total depth) and the adjacent North Bransfield Basin (693-1147 m), and used the amplicon 454-sequencing of 16S rRNA gene tags to compare the bacterial composition, diversity, and microbial community structure across environmental parameters (sediment grain size, pigments and organic nutrients) between the two areas. Marine sediments had a high abundance of heterotrophic Gammaproteobacteria (92.4% and 83.8% inside and outside the bay, respectively), followed by Alphaproteobacteria (2.5 and 5.5%), Firmicutes (1.5 and 1.6%), Bacteroidetes (1.1 and 1.7%), Deltaproteobacteria (0.8 and 2.5%) and Actinobacteria (0.7 and 1.3%). Differences in alpha-diversity and bacterial community structure were found between the two areas, reflecting the physical and chemical differences in the sediments, and the organic matter input.
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Pico and nanoplankton communities from the Southwest Atlantic Ocean along the Brazilian Bight are poorly described. The hydrography in this region is dominated by a complex system of layered water masses, which includes the warm and oligotrophic Tropical Water (TW), the cold and nutrient rich South Atlantic Central Water (SACW) and the Coastal Water (CW), which have highly variable properties. In order to assess how pico- and nanoplankton communities are distributed in these different water masses, we determined by flow cytometry the abundance of heterotrophic bacteria, Prochlorococcus, Synechococcus and autotrophic pico and nanoeukaryotes along three transects, extending from 23°S to 31°S and 39°W to 49°W. Heterotrophic bacteria (including archaea, maximum of 1.5 × 106 cells mL-1) were most abundant in Coastal and Tropical Water whereas Prochlorococcus was most abundant in open-ocean oligotrophic waters (maximum of 300 × 103 cells mL-1). Synechococcus(up to 81 × 103 cells mL-1), as well as autotrophic pico and nanoeukaryotes seemed to benefit from the influx of nutrient-rich waters near the continental slope. Autotrophic pico and nanoeukaryotes were also abundant in deep chlorophyll maximum (DCM) layers from offshore waters, and their highest abundances were 20 × 103 cells mL-1 and 5 × 103 cells mL-1, respectively. These data are consistent with previous observations in other marine areas where Synechococcus and autotrophic eukaryotes dominate mesotrophic waters, whereas Prochlorococcus dominate in more oligotrophic areas. Regardless of the microbial community structure near the surface, the carbon stock dominance by autotrophic picoeukaryotes near the DCM is possibly linked to vertical mixing of oligotrophic surface waters with the nutrient-rich SACW and their tolerance to lower light levels.
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Magnetotactic bacteria (MTB) are a heterogeneous group of ubiquitous aquatic microorganisms capable of biomineralizing nano-sized, membrane-bound, magnetic iron-rich mineral particles called magnetosomes. MTB are found in chemically-stratified aquatic sediments and/or water columns with a wide range of salinities, moderate to high temperatures, and pH varying from neutral to strongly alkaline. MTB from very cold environments have not been investigated to any great degree and here we characterize MTB from the low temperature Antarctic maritime region. Sediment samples were collected at nine sampling sites within Admiralty Bay, King George Island (62°23'S 58°27'W) from 2009 to 2013. Samples from five sites contained MTB and those from two of these sites contained large number of magnetotactic cocci that were studied using electron microscopy and molecular techniques. The magnetotactic cocci contained magnetosomes either arranged as two or four chains or as a disorganized cluster. The crystalline habit and composition of all magnetosomes analyzed with high-resolution transmission electron microscopy and energy dispersive X-ray microanalysis were consistent with elongated prismatic crystals of magnetite (Fe3 O4 ). The retrieved 16S rRNA gene sequences from magnetically-enriched magnetotactic cocci clustered into three distinct groups affiliated with the Alphaproteobacteria class of the Proteobacteria. Novel sequences of each phylogenetic cluster were confirmed using fluorescent in situ hybridization. Metagenomic data analysis of magnetically-enriched magnetotactic cocci revealed the presence of mam genes and MTB-specific hypothetical protein coding genes. Sequence homology and phylogenetic analysis indicated that predicted proteins are related to those of cultivated alphaproteobacterial MTB. The consistent and continuous low temperature of the sediment where the magnetotactic cocci are present (always below 1°C) suggests that these MTB from maritime Antarctica are psychrophiles. Moreover, similar morphotypes and 16S gene sequences were retrieved from samples collected from different sites from maritime Antarctica for several years suggesting that these new strains of MTB are indigenous members of Antarctic microbiota.