Chelatococcus albus sp. nov., a bacterium isolated from hot spring microbial mat.

A Gram-stain-negative, non-endospore-forming, motile, short rod-shaped strain, designated SYSU G07232T, was isolated from a hot spring microbial mat, sampled from Rehai National Park, Tengchong, Yunnan Province, south-western China. Strain SYSU G07232T grew at 25-50 °C (optimum, 37 °C), at pH 5.5-9.0 (optimum, pH 6.0) and tolerated NaCl concentrations up to 1.0 % (w/v). Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain SYSU G07232T showed closest genetic affinity with Chelatococcus daeguensis K106T. The genomic features and taxonomic status of this strain were determined through whole-genome sequencing and a polyphasic approach. The predominant quinone of this strain was Q-10. Major cellular fatty acids comprised C19 : 0 cyclo ω8c and summed feature 8. The whole-genome length of strain SYSU G07232T was 4.02 Mbp, and the DNA G+C content was 69.26 mol%. The average nucleotide identity (ANIm ≤84.85 % and ANIb ≤76.08  %) and digital DNA-DNA hybridization (≤ 21.9 %) values between strain SYSU G07232T and the reference species were lower than the threshold values recommended for distinguishing novel prokaryotic species. Thus, based on the provided phenotypic, phylogenetic, and genetic data, it is proposed that strain SYSU G07232T (=KCTC 8141T=GDMCC 1.4178T) be designated as representing a novel species within the genus Chelatococcus, named Chelatococcus albus sp. nov.

Molecular diversity of green-colored microbial mats from hot springs of northern Japan.

We acquired and analyzed metagenome and 16S/18S rRNA gene amplicon data of green-colored microbial mats from two hot springs within the Onikobe geothermal region (Miyagi Prefecture, Japan). The two collection sites-Tamago and Warabi-were in proximity and had the same temperature (40 °C), but the Tamago site was connected to a nearby stream, whereas the Warabi site was isolated. Both the amplicon and metagenome data suggest the bacterial, especially cyanobacterial, dominance of the mats; other abundant groups include Chloroflexota, Pseudomonadota, Bacteroidota/Chlorobiota, and Deinococcota. At finer resolution, however, the taxonomic composition entirely differed between the mats. A total of 5 and 21 abundant bacterial 16S rRNA gene OTUs were identified for Tamago and Warabi, respectively; of these, 12 are putative chlorophyll- or rhodopsin-based phototrophs. The presence of phylogenetically diverse microbial eukaryotes was noted, with ciliates and amoebozoans being the most abundant eukaryote groups for Tamago and Warabi, respectively. Fifteen metagenome-assembled genomes (MAGs) were obtained, represented by 13 bacteria, one ciliate (mitochondrion), and one giant virus. A total of 15 novel taxa, including a new deeply branching Chlorobiota species, is noted from the amplicon and MAG data, highlighting the importance of environmental sequencing in uncovering hidden microorganisms.

Cryopreservation and recovery of a complex hypersaline microbial mat community.

Cryopreservation of microorganisms is an essential tool in industrial- and food applications where conservation of microbial activity and critical beneficial traits need to be guaranteed to provide a consistent product or production process. This often refers to simple, single species or low diversity assemblages in liquid cultures that can easily be revived and regrown to perform the desired process. Cryopreservation is also of essence for scientific experimentation where many environmental samples are taken in remote sampling sites and at high costs. Biobanking, or the long term preservation and potential revival of complex, structured samples come with an additional challenge related to maintaining the structure upon revival. Here we look at cryopreserving and reviving a complex photosynthesis driven microbial mat from a hypersaline ecosystem. Amplicon sequencing of the 16S and 18S ribosomal RNA gene was used to determine the community composition of bacteria and eukaryotes respectively. The tests included the use of different cryopreservative agents and different times of cryopreservation at -150 °C. Upon revival, the cryopreservatives cannot be separated from the preserved samples without disturbing the community structure, while carryover of these compounds may influence reconstitution of the communities. Indeed, although both glycerol and Me2SO are good cryopreservatives of microbial assemblages, carryover of these compounds had a profound negative effect on the reestablishment of a functional microbial mat. Best cryopreservation and reconstitution results were obtained in the absence of a cryopreservative agent or when methanol was used.

Isotopic Signatures of Carbon Transfer in a Proterozoic Analogue Microbial Mat.

Modern microbial mats are potential analogues for Proterozoic ecosystems, yet only a few studies have characterized mats under low-oxygen conditions that are relevant to Proterozoic environments. Here, we use protein-stable isotope fingerprinting (P-SIF) to determine the protein carbon isotope (δ13C) values of autotrophic, heterotrophic, and mixotrophic organisms in a benthic microbial mat from the low-oxygen Middle Island Sinkhole, Lake Huron, USA (MIS). We also measure the δ13C values of the sugar moieties of exopolysaccharides (EPS) within the mat to explore the relationships between cyanobacterial exudates and heterotrophic anabolic carbon uptake. Our results show that Cyanobacteria (autotrophs) are 13C-depleted, relative to sulfate-reducing bacteria (heterotrophs), and 13C-enriched, relative to sulfur oxidizing bacteria (autotrophs or mixotrophs). We also find that the pentose moieties of EPS are systematically enriched in 13C, relative to the hexose moieties of EPS. We hypothesize that these isotopic patterns reflect cyanobacterial metabolic pathways, particularly phosphoketolase, that are relatively more active in low-oxygen mat environments, rather than oxygenated mat environments. This results in isotopically more heterogeneous C sources in low-oxygen mats. While this might partially explain the isotopic variability observed in Proterozoic mat facies, further work is necessary to systematically characterize the isotopic fractionations that are associated with the synthesis of cyanobacterial exudates. IMPORTANCE The δ13C compositions of heterotrophic microorganisms are dictated by the δ13C compositions of their organic carbon sources. In both modern and ancient photosynthetic microbial mats, photosynthetic exudates are the most likely source of organic carbon for heterotrophs. We measured the δ13C values of autotrophic, heterotrophic, and mixotrophic bacteria as well as the δ13C value of the most abundant photosynthetic exudate (exopolysaccharide) in a modern analogue for a Proterozoic environment. Given these data, future studies will be better equipped to estimate the most likely carbon source for heterotrophs in both modern environments as well as in Proterozoic environments preserved in the rock record.

With a pinch of salt: metagenomic insights into Namib Desert salt pan microbial mats and halites reveal functionally adapted and competitive communities.

IMPORTANCE: The hyperarid Namib Desert is one of the oldest deserts on Earth. It contains multiple clusters of playas which are saline-rich springs surrounded by halite evaporites. Playas are of great ecological importance, and their indigenous (poly)extremophilic microorganisms are potentially involved in the precipitation of minerals such as carbonates and sulfates and have been of great biotechnological importance. While there has been a considerable amount of microbial ecology research performed on various Namib Desert edaphic microbiomes, little is known about the microbial communities inhabiting its multiple playas. In this work, we provide a comprehensive taxonomic and functional potential characterization of the microbial, including viral, communities of sediment mats and halites from two distant salt pans of the Namib Desert, contributing toward a better understanding of the ecology of this biome.

Caldovatus aquaticus sp. nov., a moderately thermophilic bacterium isolated from hot spring microbial mat.

Two closely related, aerobic, Gram-stain-negative, motile, oval-shaped, non-endospore-forming, moderately thermophilic bacteria, designated strains SYSU G05006T and SYSU G05005, were isolated from a bioreactor enrichment and the original sample was collected from Rehai National Park, Tengchong, Yunnan Province, PR China. The results of phylogenetic analysis based on the 16S rRNA gene sequences indicated that these two strains were closely related to Caldovatus sediminis YIM 72346T (96.75 and 96.89 % sequence similarity, respectively). The whole genome size of strain SYSU G05006T was 3.87 Mbp with a DNA G+C content of 75.33 mol%. The average nucleotide identity (ANI based on the MUMmer algorithm≤90.31 % and ANI based on blast≤89.36 %) and digital DNA-DNA hybridization (≤35.10 %) values between strain SYSU G05006T and other members of the family Acetobacteraceae were all lower than the threshold values recommended for distinguishing novel prokaryotic species. Optimal growth of the strain was observed at 55 °C and pH 6.0. Ubiquinone-10 was the predominant respiratory lipoquinone. The major cellular fatty acids included iso-C14 : 0, C16 : 1 ω5c, summed feature 5 and summed feature 7. The major polar lipids consisted of diphosphatidylglycerol, one unidentified aminolipid, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, two unidentified phospholipids and two unidentified lipids. Based on results of phylogenetic analyses, comparative genomics and phenotypic characteristics, we describe a new species of the genus Caldovatus represented by strain SYSU G05006T (=KCTC 82831T=MCCC 1K06125T), for which we propose the name Caldovatus aquaticus sp. nov.

Photochemical changes during rehydration of an intertidal cyanobacterial mat exposed to variations in salinity and light intensity.

This study focuses on a Lyngbya cf. aestuarii dominated mat community from the intertidal zone of the Laguna Ojo de Liebre, Baja California Sur. In this environment, the mat is desiccated for several days between spring tides. While the mats were desiccated, photosynthetic activity was absent but recovered rapidly (~3 h) upon rehydration. It has been shown previously that the rate of photosynthetic recovery is dependent on both light intensity and salinity. In the current study, photosynthetic recovery was measured based on chlorophyll a fluorescence using pulse amplitude modulated (PAM) fluorometry. Upon the addition of water, photosystem II (PSII) complexes recovered the capacity for reaction centre excitation. However, these functional centres were initially closed. Respiratory activity early in recovery probably reduced the plastoquinone pool through the shared use of part of the photosynthetic transport chain, thus temporarily blocking electron transport downstream of PSII. The time that PSII complexes remained closed increased with light intensities above saturation. This condition is potentially damaging to the cyanobacteria since the exposure of closed PSII centres to high light intensities can lead to the production of singlet oxygen. After this initial lag period, PSII centres opened rapidly indicating an increase in the flow of electrons from PSII to PSI. The rate of photosynthetic recovery appeared to be limited primarily by the relatively slow return of functional PSII. Photosynthetic recovery rates were slower in salinities greater than those that naturally occur in the intertidal zone.

Phosphate-Arsenic Interactions in Halophilic Microorganisms of the Microbial Mat from Laguna Tebenquiche: from the Microenvironment to the Genomes.

Arsenic (As) is a metalloid present in the earth's crust and widely distributed in the environment. Due to its high concentrations in the Andean valleys and its chemical similarity with phosphorus (P), its biological role in Andean Microbial Ecosystems (AMEs) has begun to be studied. The AMEs are home to extremophilic microbial communities that form microbial mats, evaporites, and microbialites inhabiting Andean lakes, puquios, or salt flats. In this work, we characterize the biological role of As and the effect of phosphate in AMEs from the Laguna Tebenquiche (Atacama Desert, Chile). Using micro X-ray fluorescence, the distribution of As in microbial mat samples was mapped. Taxonomic and inferred functional profiles were obtained from enriched cultures of microbial mats incubated under As stress and different phosphate conditions. Additionally, representative microorganisms highly resistant to As and able to grow under low phosphate concentration were isolated and studied physiologically. Finally, the genomes of the isolated Salicola sp. and Halorubrum sp. were sequenced to analyze genes related to both phosphate metabolism and As resistance. The results revealed As as a key component of the microbial mat ecosystem: (i) As was distributed across all sections of the microbial mat and represented a significant weight percentage of the mat (0.17 %) in comparison with P (0.40%); (ii) Low phosphate concentration drastically changed the microbial community in microbial mat samples incubated under high salinity and high As concentrations; (iii) Archaea and Bacteria isolated from the microbial mat were highly resistant to arsenate (up to 500 mM), even under low phosphate concentration; (iv) The genomes of the two isolates were predicted to contain key genes in As metabolism (aioAB and arsC/acr3) and the genes predicted to encode the phosphate-specific transport operon (pstSCAB-phoU) are next to the arsC gene, suggesting a functional relationship between these two elements.

The microalga Haematococcus lacustris (Chlorophyceae) forms natural biofilms in supralittoral White Sea coastal rock ponds.

MAIN CONCLUSION: Haematococcus lacustris inhabits supralittoral rock ponds and forms, under natural conditions, biofilms including layered cyanobacterial and fermentative microbial mats. Dry mats, formed under extremely stressful conditions, contained only haematocysts. Under favorable growth conditions, modeled for dry biofilms in vitro, microalgal free-living stages were detected. Haematococcus lacustris is the microalga known for its high potential to survive under a wide range of unfavorable conditions, particularly in the supralittoral temporal rock ponds of the White Sea. Previously, we described microbial communities containing H. lacustris in this region. In many cases, they were organized into systems exhibiting complex three-dimensional structure similar to that of natural biofilms. In this study, for the first time, we clarify structural description and provide microscopic evidence that these communities of H. lacustris and bacteria are assembled into the true biofilms. There are (1) simple single layer biofilms on the surface of rocks and macrophytic algae, (2) floccules (or flocs) not attached to a surface, (3) as well as stratified (layered) biofilms, wet, and dehydrated in nature. Being involved into primary organic production, H. lacustris and cyanobacteria are located exclusively in the upper layers of stratified biofilms, where they are capable to absorb sufficient for photosynthesis amount of light. The presence of acidic polysaccharides in the extracellular matrix revealed by specific staining with ruthenium red in the H. lacustris-containing microbial communities is a biochemical evidence of biofilm formation. Meanwhile, the presence of bacterial L-form is an ultrastructural confirmation of that fact. Under favorable conditions, modeled in vitro, H. lacustris from the dry microbial mats moves to the free-living states represented by vegetative palmelloid cells and motile zoospores. Owing to the fact that inside biofilms cells of microorganisms exist under stable conditions, we consider the biofilm formation as an additional mechanism that contributes to the survival of H. lacustris in the supralittoral zone of the White Sea.

Short-Term Stable Isotope Probing of Proteins Reveals Taxa Incorporating Inorganic Carbon in a Hot Spring Microbial Mat.

The upper green layer of the chlorophototrophic microbial mats associated with the alkaline siliceous hot springs of Yellowstone National Park consists of oxygenic cyanobacteria (Synechococcus spp.), anoxygenic Roseiflexus spp., and several other anoxygenic chlorophototrophs. Synechococcus spp. are believed to be the main fixers of inorganic carbon (Ci), but some evidence suggests that Roseiflexus spp. also contribute to inorganic carbon fixation during low-light, anoxic morning periods. Contributions of other phototrophic taxa have not been investigated. In order to follow the pathway of Ci incorporation into different taxa, mat samples were incubated with [13C]bicarbonate for 3 h during the early-morning, low-light anoxic period. Extracted proteins were treated with trypsin and analyzed by mass spectrometry, leading to peptide identifications and peptide isotopic profile signatures containing evidence of 13C label incorporation. A total of 25,483 peptides, corresponding to 7,221 proteins, were identified from spectral features and associated with mat taxa by comparison to metagenomic assembly sequences. A total of 1,417 peptides, derived from 720 proteins, were detectably labeled with 13C. Most 13C-labeled peptides were derived from proteins of Synechococcus spp. and Roseiflexus spp. Chaperones and proteins of carbohydrate metabolism were most abundantly labeled. Proteins involved in photosynthesis, Ci fixation, and N2 fixation were also labeled in Synechococcus spp. Importantly, most proteins of the 3-hydroxypropionate bi-cycle for Ci fixation in Roseiflexus spp. were labeled, establishing that members of this taxocene contribute to Ci fixation. Other taxa showed much lower [13C]bicarbonate incorporation.IMPORTANCE Yellowstone hot spring mats have been studied as natural models for understanding microbial community ecology and as modern analogs of stromatolites, the earliest community fossils on Earth. Stable-isotope probing of proteins (Pro-SIP) permitted short-term interrogation of the taxa that are involved in the important process of light-driven Ci fixation in this highly active community and will be useful in linking other metabolic processes to mat taxa. Here, evidence is presented that Roseiflexus spp., which use the 3-hydroxypropionate bi-cycle, are active in Ci fixation. Because this pathway imparts a lower degree of selection of isotopically heavy Ci than does the Calvin-Benson-Bassham cycle, the results suggest a mechanism to explain why the natural abundance of 13C in mat biomass is greater than expected if only the latter pathway were involved. Understanding how mat community members influence the 13C/12C ratios of mat biomass will help geochemists interpret the 13C/12C ratios of organic carbon in the fossil record.

Relationship between Microorganisms Inhabiting Alkaline Siliceous Hot Spring Mat Communities and Overflowing Water.

The compositions of Octopus Spring and Mushroom Spring (Yellowstone National Park, Wyoming, USA) microbial mats have been thoroughly studied, but the compositions of the effluent waters that flow above the mats have not. In this study, cells in the mats and overflowing waters of both springs were investigated at multiple sites where Synechococcus spp. are the dominant cyanobacteria (ca. 72°C to ca. 50°C), and on several dates. In addition to microscopic analyses of stained and autofluorescent cells, 16S rRNA gene sequencing was used to characterize the major taxa present and a protein-encoding gene (psaA) was sequenced and analyzed by ecotype simulation to predict species of Synechococcus The mats of both springs were similar in terms of the downstream distribution of predominant taxa detected previously. However, waters above these mats were predominated by taxa that reside in upstream mats or communities above the upper-temperature limit of the mat. A disturbance/recolonization study was performed at a site normally predominated by Synechococcus species adapted to low temperatures. After removing indigenous Synechococcus cells, Synechococcus species adapted to higher temperatures, which were predominant in the water overflowing this site, colonized the newly forming mat. Differences in recolonization under reduced and UV-screened irradiance suggested that, in addition to physical transport, environmental conditions likely select for species that are better adapted to these different conditions and can influence mat recovery. A transport model was developed and used to predict that, in Mushroom Spring, erosion predominates in the narrower and deeper upstream effluents and deposition predominates over erosion in wider and shallower downstream effluents.IMPORTANCE In flowing aquatic systems, cell erosion and deposition are important to the dispersal of cells from one location to another. Very little is known about microbial dispersal and the physical processes that underlie it. This study demonstrates its importance to colonization of downstream surfaces and especially to the recolonization and functioning of disturbed sites. Ecological systems in flowing environments are often, roughly speaking, pseudosteady, in that nutrients enter the system and by-products leave at relatively steady rates. Over time, material inputs and outputs must balance. Measurements of input fluxes (e.g., growth rates and proxies, such as photosynthesis rates) are frequent. However, erosion and deposition of cells are seldom measured and ecological significance is sometimes neglected. The importance of these parameters is immediately evident in any attempt to construct a model of long-time community behavior, as spatial ecological structure is significantly impacted and can be dominated by migration of organisms, even in small numbers.

Microbial community composition and dolomite formation in the hypersaline microbial mats of the Khor Al-Adaid sabkhas, Qatar.

The Khor Al-Adaid sabkha in Qatar is among the rare extreme environments on Earth where it is possible to study the formation of dolomite-a carbonate mineral whose origin remains unclear and has been hypothetically linked to microbial activity. By combining geochemical measurements with microbiological analysis, we have investigated the microbial mats colonizing the intertidal areas of sabhka. The main aim of this study was to identify communities and conditions that are favorable for dolomite formation. We inspected and sampled two locations. The first site was colonized by microbial mats that graded vertically from photo-oxic to anoxic conditions and were dominated by cyanobacteria. The second site, with higher salinity, had mats with an uppermost photo-oxic layer dominated by filamentous anoxygenic photosynthetic bacteria (FAPB), which potentially act as a protective layer against salinity for cyanobacterial species within the deeper layers. Porewater in the uppermost layers of the both investigated microbial mats was supersaturated with respect to dolomite. Corresponding to the variation of the microbial community's vertical structure, a difference in crystallinity and morphology of dolomitic phases was observed: dumbbell-shaped proto-dolomite in the mats dominated by cyanobacteria and rhombohedral ordered-dolomite in the mat dominated by FAPB.

SSU-rRNA Gene Sequencing Survey of Benthic Microbial Eukaryotes from Guaymas Basin Hydrothermal Vent.

Microbial eukaryotes have important roles in marine food webs, but their diversity and activities in hydrothermal vent ecosystems are poorly characterized. In this study, we analyzed microbial eukaryotic communities associated with bacterial (Beggiatoa) mats in the 2,000 m deep-sea Guaymas Basin hydrothermal vent system using 18S rRNA gene high-throughput sequencing of the V4 region. We detected 6,954 distinct Operational Taxonomic Units (OTUs) across various mat systems. Of the sequences that aligned with known protistan phylotypes, most were affiliated with alveolates (especially dinoflagellates and ciliates) and cercozoans. OTU richness and community structure differed among sediment habitats (e.g. different mat types and cold sediments away from mats). Additionally, full-length 18S rRNA genes amplified and cloned from single cells revealed the identities of some of the most commonly encountered, active ciliates in this hydrothermal vent ecosystem. Observations and experiments were also conducted to demonstrate that ciliates were trophically active and ingesting fluorescent bacteria or Beggiatoa trichomes. Our work suggests that the active and diverse protistan community at the Guaymas Basin hydrothermal vent ecosystem likely consumes substantial amounts of bacterial biomass, and that the different habitats, often defined by distances of just a few 10s of cm, select for particular assemblages and levels of diversity.

Radiative Energy Budgets in a Microbial Mat Under Different Irradiance and Tidal Conditions.

Irradiance and temperature variations during tidal cycles modulate microphytobenthic primary production potentially by changing the radiative energy balance of photosynthetic mats between immersion and emersion and thus sediment daily net metabolism. To test the effect of tidal stages on the radiative energy budget, we used microsensor measurements of oxygen, temperature, and scalar irradiance to estimate the radiative energy budget in a coastal photosynthetic microbial mat during immersion (constant water column of 2 cm) and emersion under increasing irradiance. Total absorbed light energy was higher in immersion than emersion, due to a lower reflectance of the microbial mat, while most (> 97%) of the absorbed light energy was dissipated as heat irrespective of tidal conditions. During immersion, the upward heat flux was higher than the downward one, whereas the opposite occurred during emersion. At highest photon irradiance (800 µmol photon m-2 s-1), the sediment temperature increased ~ 2.5 °C after changing the conditions from immersion to emersion. The radiative energy balance showed that less than 1% of the incident light energy (PAR, 400-700 nm) was conserved by photosynthesis under both tidal conditions. At low to moderate incident irradiances, the light use efficiency was similar during the tidal stages. In contrast, we found an ~ 30% reduction in the light use efficiency during emersion as compared to immersion under the highest irradiance likely due to the rapid warming of the sediment during emersion and increased non-photochemical quenching. These changes in the photosynthetic efficiency and radiative energy budget could affect both primary producers and temperature-dependent bacterial activity and consequently daily net metabolism rates having important ecological consequences.

Methanogenic and Sulfate-Reducing Activities in a Hypersaline Microbial Mat and Associated Microbial Diversity.

Methanogenesis and sulfate reduction are important microbial processes in hypersaline environments. However, key aspects determining substrate competition between these microbial processes have not been well documented. We evaluated competitive and non-competitive substrates for stimulation of both processes through microcosm experiments of hypersaline microbial mat samples from Guerrero Negro, Baja California Sur, Mexico, and we assessed the effect of these substrates on the microbial community composition. Methylotrophic methanogenesis evidenced by sequences belonging to methanogens of the family Methanosarcinaceae was found as the dominant methanogenic pathway in the studied hypersaline microbial mat. Nevertheless, our results showed that incubations supplemented with acetate and lactate, performed in absence of sulfate, also produced methane after 40 days of incubation, apparently driven by hydrogenotrophic methanogens affiliated to the family Methanomicrobiaceae. Sulfate reduction was mainly stimulated by addition of acetate and lactate; however, after 40 days of incubation, an increase of the H2S concentrations in microcosms amended with trimethylamine and methanol was also observed, suggesting that these substrates are putatively used for sulfate reduction. Moreover, 16S rRNA gene sequencing analysis showed remarkable differences in the microbial community composition among experimental treatments. In the analyzed sample amended with acetate, sulfate-reducing bacteria (SRB) belonging to the family Desulfobacteraceae were dominant, while members of Desulfohalobiaceae, Desulfomicrobiaceae, and Desulfovibrionaceae were found in the incubation with lactate. Additionally, we detected an unexpected high abundance of unclassified Hydrogenedentes (near 25%) in almost all the experimental treatments. This study contributes to better understand methanogenic and sulfate-reducing activities, which play an important role in the functioning of hypersaline environments.

Rhodobacter sp. Rb3, an aerobic anoxygenic phototroph which thrives in the polyextreme ecosystem of the Salar de Huasco, in the Chilean Altiplano.

The Salar de Huasco is an evaporitic basin located in the Chilean Altiplano, which presents extreme environmental conditions for life, i.e. high altitude (3800 m.a.s.l.), negative water balance, a wide salinity range, high daily temperature changes and the occurrence of the highest registered solar radiation on the planet (> 1200 W m-2). This ecosystem is considered as a natural laboratory to understand different adaptations of microorganisms to extreme conditions. Rhodobacter, an anoxygenic aerobic phototrophic bacterial genus, represents one of the most abundant groups reported based on taxonomic diversity surveys in this ecosystem. The bacterial mat isolate Rhodobacter sp. strain Rb3 was used to study adaptation mechanisms to stress-inducing factors potentially explaining its success in a polyextreme ecosystem. We found that the Rhodobacter sp. Rb3 genome was characterized by a high abundance of genes involved in stress tolerance and adaptation strategies, among which DNA repair and oxidative stress were the most conspicuous. Moreover, many other molecular mechanisms associated with oxidative stress, photooxidation and antioxidants; DNA repair and protection; motility, chemotaxis and biofilm synthesis; osmotic stress, metal, metalloid and toxic anions resistance; antimicrobial resistance and multidrug pumps; sporulation; cold shock and heat shock stress; mobile genetic elements and toxin-antitoxin system were detected and identified as potential survival mechanism features in Rhodobacter sp. Rb3. In total, these results reveal a wide set of strategies used by the isolate to adapt and thrive under environmental stress conditions as a model of polyextreme environmental resistome.

Distribution of greenhouse gases in hyper-arid and arid areas of northern Chile and the contribution of the high altitude wetland microbiome (Salar de Huasco, Chile).

Northern Chile harbors different bioclimatic zones including hyper-arid and arid ecosystems and hotspots of microbial life, such as high altitude wetlands, which may contribute differentially to greenhouse gases (GHG) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). In this study, we explored ground level GHG distribution and the potential role of a wetland situated at 3800 m.a.s.l, and characterized by high solar radiation < 1600 W m-2, extreme temperature ranges (-12 to 24 °C) and wind stress (< 17 m s-1). The water source of the wetland is mainly groundwater springs, which generates streams and ponds surrounded by peatlands. These sites support a rich microbial aquatic life including diverse bacteria and archaea communities, which transiently form more complex structures, such as microbial mats. In this study, GHG were measured in the water and above ground level air at the wetland site and along an elevation gradient in different bioclimatic areas from arid to hyper-arid zones. The microbiome from the water and sediments was described by high-throughput sequencing 16S rRNA and rDNA genes. The results indicate that GHG at ground level were variable along the elevation gradient potentially associated with different bioclimatic zones, reaching high values at the high Andean steppe and variable but lower values in the Atacama Desert and at the wetland. The water areas of the wetland presented high concentrations of CH4 and CO2, particularly at the spring areas and in air bubbles below microbial mats. The microbial community was rich (> 40 phyla), including archaea and bacteria potentially active in the different matrices studied (water, sediments and mats). Functional microbial groups associated with GHG recycling were detected at low frequency, i.e., < 2.5% of total sequences. Our results indicate that hyper-arid and arid areas of northern Chile are sites of GHG exchange associated with various bioclimatic zones and particularly in aquatic areas of the wetland where this ecosystem could represent a net sink of N2O and a source for CH4 and CO2.

Matworld - the biogeochemical effects of early life on land.

Contents 531 I. 531 II. 532 III. 534 IV. 535 V. 535 VI. 535 Acknowledgements 536 References 536 SUMMARY: There is growing evidence that life has been on land for billions of years. Microbial mats fuelled by oxygenic photosynthesis were probably present in terrestrial habitats from c. 3.0 billion yr ago (Ga) onwards, creating localized 'oxygen oases' under a reducing atmosphere, which left a characteristic oxidative weathering signal. After the Great Oxidation c. 2.4 Ga, the now oxidizing atmosphere masked that redox signal, but ancient soils record the mobilization of phosphorus and other elements by organic acids in weathering profiles. Evidence for Neoproterozoic 'greening of the land' and intensification of weathering c. 0.85-0.54 Ga is currently equivocal. However, the mid-Palaeozoic c. 0.45-0.4 Ga shows global atmospheric changes consistent with increased terrestrial productivity and intensified weathering by the first land plants.

Bioprospecting Red Sea Coastal Ecosystems for Culturable Microorganisms and Their Antimicrobial Potential.

Microorganisms that inhabit unchartered unique soil such as in the highly saline and hot Red Sea lagoons on the Saudi Arabian coastline, represent untapped sources of potentially new bioactive compounds. In this study, a culture-dependent approach was applied to three types of sediments: mangrove mud (MN), microbial mat (MM), and barren soil (BS), collected from Rabigh harbor lagoon (RHL) and Al-Kharrar lagoon (AKL). The isolated bacteria were evaluated for their potential to produce bioactive compounds. The phylogenetic characterization of 251 bacterial isolates based on the 16S rRNA gene sequencing, supported their assignment to five different phyla: Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, and Planctomycetes. Fifteen putative novel species were identified based on a 16S rRNA gene sequence similarity to other strain sequences in the NCBI database, being ≤98%. We demonstrate that 49 of the 251 isolates exhibit the potential to produce antimicrobial compounds. Additionally, at least one type of biosynthetic gene sequence, responsible for the synthesis of secondary metabolites, was recovered from 25 of the 49 isolates. Moreover, 10 of the isolates had a growth inhibition effect towards Staphylococcus aureus, Salmonella typhimurium and Pseudomonas syringae. We report the previously unknown antimicrobial activity of B. borstelensis, P. dendritiformis and M. salipaludis against all three indicator pathogens. Our study demonstrates the evidence of diverse cultured microbes associated with the Red Sea harbor/lagoon environments and their potential to produce antimicrobial compounds.

Metagenome-assembled bacterial genomes from benthic microbial mats in ice-covered Lake Vanda, Antarctica.

We recovered 57 bacterial metagenome-assembled genomes (MAGs) from benthic microbial mat pinnacles from Lake Vanda, Antarctica. These MAGs provide access to genomes from polar environments and can assist in culturing and utilizing these Antarctic bacteria.