Determinants of Microbial-Derived Dissolved Organic Matter Diversity in Antarctic Lakes.

Identifying drivers of the molecular composition of dissolved organic matter (DOM) is essential to understand the global carbon cycle, but an unambiguous interpretation of observed patterns is challenging due to the presence of confounding factors that affect the DOM composition. Here, we show, by combining ultrahigh-resolution mass spectrometry and nuclear magnetic resonance spectroscopy, that the DOM molecular composition varies considerably among 43 lakes in East Antarctica that are isolated from terrestrial inputs and human influence. The DOM composition in these lakes is primarily driven by differences in the degree of photodegradation, sulfurization, and pH. Remarkable molecular beta-diversity of DOM was found that rivals the dissimilarity between DOM of rivers and the deep ocean, which was driven by environmental dissimilarity rather than the spatial distance. Our results emphasize that the extensive molecular diversity of DOM can arise even in one of the most pristine and organic matter source-limited environments on Earth, but at the same time the DOM composition is predictable by environmental variables and the lakes' ecological history.

Dissolved Organic Matter Processing in Pristine Antarctic Streams.

Accelerated glacier melt and runoff may lead to inputs of labile dissolved organic matter (DOM) to downstream ecosystems and stimulate the associated biogeochemical processes. However, still little is known about glacial DOM composition and its downstream processing before entering the ocean, although the function of DOM in food webs and ecosystems largely depends on its composition. Here, we employ a set of molecular and optical techniques (UV-vis absorption and fluorescence spectroscopy, 1H NMR, and ultrahigh-resolution mass spectrometry) to elucidate the composition of DOM in Antarctic glacial streams and its downstream change. Glacial DOM consisted largely of a mixture of small microbial-derived biomolecules. 1H NMR analysis of bulk water revealed that these small molecules were processed downstream into more complex, structurally unrecognizable molecules. The extent of processing varied between streams. By applying multivariate statistical (compositional data) analysis of the DOM molecular data, we identified molecular compounds that were tightly associated and moved in parallel in the glacial streams. Lakes in the middle of the flow paths enhanced water residence time and allowed for both more DOM processing and production. In conclusion, downstream processing of glacial DOM is substantial in Antarctica and affects the amounts of biologically labile substrates that enter the ocean.

Water column gradients beneath the summer ice of a High Arctic freshwater lake as indicators of sensitivity to climate change.

Ice cover persists throughout summer over many lakes at extreme polar latitudes but is likely to become increasingly rare with ongoing climate change. Here we addressed the question of how summer ice-cover affects the underlying water column of Ward Hunt Lake, a freshwater lake in the Canadian High Arctic, with attention to its vertical gradients in limnological properties that would be disrupted by ice loss. Profiling in the deepest part of the lake under thick mid-summer ice revealed a high degree of vertical structure, with gradients in temperature, conductivity and dissolved gases. Dissolved oxygen, nitrous oxide, carbon dioxide and methane rose with depth to concentrations well above air-equilibrium, with oxygen values at > 150% saturation in a mid-water column layer of potential convective mixing. Fatty acid signatures of the seston also varied with depth. Benthic microbial mats were the dominant phototrophs, growing under a dim green light regime controlled by the ice cover, water itself and weakly colored dissolved organic matter that was mostly autochthonous in origin. In this and other polar lakes, future loss of mid-summer ice will completely change many water column properties and benthic light conditions, resulting in a markedly different ecosystem regime.

Ammonia Oxidation Potentials and Ammonia Oxidizers of Lichen-Moss Vegetated Soils at Two Ice-free Areas in East Antarctica.

The maximum ammonia oxidation potential (AOP) of a topsoil in Langhovde, East Antarctica was 22.1±2.4| |ng N g-1 dry soil h-1 (2| |mM ammonium, 10°C, n=3). This topsoil exhibited twin AOP peaks (1 and 2| |mM ammonium) at 10°C, but not at 20°C. Six and ten operational taxonomic units (OTUs) were identified for ammonia-oxidizing bacteria (AOB) and archaea (AOA) amoA, respectively. AOB were classified into Nitrosospira; the two dominant OTUs corresponded to the Mount Everest cluster. AOA were classified into three clusters; Nitrososphaera and Nitrosocosmicus were the two dominant clusters.

Origin, distributions, and environmental significance of ubiquitous humic-like fluorophores in Antarctic lakes and streams.

This study characterized dissolved organic matter (DOM) obtained from 47 lakes and 2 streams on ice-free areas at Lützow-Holm Bay and Amundsen Bay in East Antarctica (n = 74), where few biogeochemical studies have been historically conducted. Samples were analyzed for basic water chemistry and by resin fractionation, UV-vis spectroscopy, and excitation emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC). Salinity of the samples ranged very broadly from fresh to hypersaline as a result of evaporative concentration. There was a clear positive correlation between log-salinity and the spectral slopes of DOM (S275-295), an indicator of photodegradation. Thus, we interpreted the correlation as a progression of photodegradation by prolonged water retention time. Of the identified seven PARAFAC components, three ubiquitous humic-like components decreased as photodegradation progressed, while a photorefractory UVC humic-like component increased its relative abundance. A non-humic component, traditionally defined as Peak N, did not show a trend depending on photodegradation, and its level was high in nutrient-rich lakes, presumably due to high in-situ production. We found robust correlations between the relative abundance of the ubiquitous humic-like components and that of the Peak N component in the bulk DOM irrespective of water types or ice-free areas. We proposed there were common processes that generated the ubiquitous humic-like components from the Peak N component in the Lützow-Holm Bay and Amundsen Bay lakes and streams, such as bacterial processing of primary production-derived DOM and photochemical transformation of microbial DOM.

Light quality determines primary production in nutrient-poor small lakes.

The availability of nutrients for primary producers has long been thought to be the main limiting factor for primary productivity in nutrient-poor lake ecosystems. However, recent studies have indicated that the availability of light energy is also important. On the other hand, the amount of phototroph was reported to decrease in summer in Antarctic lakes, furthermore, the light environment underwater was shown containing high amount of ultraviolet energy in small Antarctic lakes. Here, we hypothesized that primary productivity is limited by not only nutrients and simple light quantity but also light quality in nutrient-poor lakes. Then, we investigate factors influencing primary production by benthic phototrophic communities in shallow nutrient-poor lakes. We examine the relationships between primary production in 17 Antarctic freshwater lakes and nutrient concentrations in lake and benthic water, temperature and light energy. Primary production is decreased by ultraviolet energy reaching the lake bed, showing that production is determined by light quality. We also correlate ultraviolet energy in lake water with the catchment area of each lake. Our results show that the underwater light environment has an important influence on primary production as a key limitation factor and is sensitive to materials in runoff from the surrounding environment for pristine lakes.

Vishniacozyma ellesmerensis sp. nov., a psychrophilic yeast isolated from a retreating glacier in the Canadian High Arctic.

Two strains of a psychrophilic basidiomycetous yeast species belonging to the genus Vishniacozyma were isolated from sediments and soil at the front of a retreating glacier on northern Ellesmere Island in the Canadian Arctic. Analysis of the large subunit D1/D2 region and the internal transcribed spacer (ITS) regions of the rDNA indicated that these strains represented a novel species. The closest relatives of the novel species were Vishniacozyma globispora and V. dimennae, which exhibited sequence similarities of 82.2 and 81.6 %, respectively, to the ITS region of the novel species, and contained 61 and 57 nt substitutions, respectively, in the D1/D2 domain, in comparison with the novel species. Strains of the novel species were able to grow at sub-zero temperatures and in vitamin-free medium. These characteristics allow the strains to survive and grow in perennially cold, oligotrophic habitats in the Canadian High Arctic. The name Vishniacozyma ellesmerensis sp. nov. is proposed. The type strain is JCM 32573T (=UAMH 11973T=G3-4-8T) and the MycoBank number is MB825501.

Mrakia hoshinonis sp. nov., a novel psychrophilic yeast isolated from a retreating glacier on Ellesmere Island in the Canadian High Arctic.

Four strains isolated from sediment sampled at the front of a retreating glacier on northern Ellesmere Island in the Canadian high Arctic, namely JCM 32575T, JCM 32576, JCM 32577 and JCM 32578, belong to a novel psychrophilic basidiomycetous yeast species in the genus Mrakia. Molecular phylogenetic analysis indicated that these strains are most closely related to the type strains of Mrakia aquatica and Mrakianic combsii, but with 8-9 and 7-12 nt substitutions in ITS and in the D1/D2 domain of the LSU rRNA gene, respectively. The strains grew at sub-zero temperatures and in vitamin-free media, with lipase and cellulase highly active even at -3 °C. These characteristics likely allow this yeast species to grow and survive in extremely cold, oligotrophic environments, such as the fronts of retreating glaciers in the high Arctic. The name Mrakia hoshinonis sp. nov. is proposed, with type strain JCM 32575T (UAMH 11969) and MycoBank number MB 825484.

Seabird-affected taluses are denitrification hotspots and potential N2O emitters in the High Arctic.

In High Arctic tundra ecosystems, seabird colonies create nitrogen cycling hotspots because of bird-derived labile organic matter. However, knowledge about the nitrogen cycle in such ornithocoprophilous tundra is limited. Here, we determined denitrification potentials and in-situ nitrous oxide (N2O) emissions of surface soils on plant-covered taluses under piscivorous seabird cliffs at two sites (BL and ST) near Ny-Ålesund, Svalbard, in the European High Arctic. Talus soils at both locations had very high denitrification potentials at 10 °C (2.62-4.88 mg N kg-1 dry soil h-1), near the mean daily maximum air temperature in July in Ny-Ålesund, with positive temperature responses at 20 °C (Q10 values, 1.6-2.3). The talus soils contained abundant denitrification genes, suggesting that they are denitrification hotspots. However, high in-situ N2O emissions, indicating the presence of both active aerobic nitrification and anaerobic denitrification, were observed only at BL (max. 16.6 µg N m-2 h-1). Rapid nitrogen turnover at BL was supported by lower carbon-to-nitrogen ratios, higher nitrate content, and higher δ15N values in the soils at BL compared with those at ST. These are attributed to the 30-fold larger seabird density at BL than at ST, providing the larger organic matter input.

Microbial Communities and Their Predicted Metabolic Functions in Growth Laminae of a Unique Large Conical Mat from Lake Untersee, East Antarctica.

In this study, we report the distribution of microbial taxa and their predicted metabolic functions observed in the top (U1), middle (U2), and inner (U3) decadal growth laminae of a unique large conical microbial mat from perennially ice-covered Lake Untersee of East Antarctica, using NextGen sequencing of the 16S rRNA gene and bioinformatics tools. The results showed that the U1 lamina was dominated by cyanobacteria, specifically Phormidium sp., Leptolyngbya sp., and Pseudanabaena sp. The U2 and U3 laminae had high abundances of Actinobacteria, Verrucomicrobia, Proteobacteria, and Bacteroidetes. Closely related taxa within each abundant bacterial taxon found in each lamina were further differentiated at the highest taxonomic resolution using the oligotyping method. PICRUSt analysis, which determines predicted KEGG functional categories from the gene contents and abundances among microbial communities, revealed a high number of sequences belonging to carbon fixation, energy metabolism, cyanophycin, chlorophyll, and photosynthesis proteins in the U1 lamina. The functional predictions of the microbial communities in U2 and U3 represented signal transduction, membrane transport, zinc transport and amino acid-, carbohydrate-, and arsenic- metabolisms. The Nearest Sequenced Taxon Index (NSTI) values processed through PICRUSt were 0.10, 0.13, and 0.11 for U1, U2, and U3 laminae, respectively. These values indicated a close correspondence with the reference microbial genome database, implying high confidence in the predicted metabolic functions of the microbial communities in each lamina. The distribution of microbial taxa observed in each lamina and their predicted metabolic functions provides additional insight into the complex microbial ecosystem at Lake Untersee, and lays the foundation for studies that will enhance our understanding of the mechanisms responsible for the formation of these unique mat structures and their evolutionary significance.

D2d(23)-C84 versus Sc2C2@D2d(23)-C84: Impact of Endohedral Sc2C2 Doping on Chemical Reactivity in the Photolysis of Diazirine.

We compared the chemical reactivity of D2d(23)-C84 and that of Sc2C2@D2d(23)-C84, both having the same carbon cage geometry, in the photolysis of 2-adamantane-2,3'-[3H]-diazirine, to clarify metal-atom doping effects on the chemical reactivity of the carbon cage. Experimental and computational studies have revealed that the chemical reactivity of the D2d(23)-C84 carbon cage is altered drastically by endohedral Sc2C2 doping. The reaction of empty D2d(23)-C84 with the diazirine under photoirradiation yields two adamantylidene (Ad) adducts. NMR spectroscopic studies revealed that the major Ad monoadduct (C84(Ad)-A) has a fulleroid structure and that the minor Ad monoadduct (C84(Ad)-B) has a methanofullerene structure. The latter was also characterized using X-ray crystallography. C84(Ad)-A is stable under photoirradiation, but it interconverted to C84(Ad)-B by heating at 80 °C. In contrast, the reaction of endohedral Sc2C2@D2d(23)-C84 with diazirine under photoirradiation affords four Ad monoadducts (Sc2C2@C84(Ad)-A, Sc2C2@C84(Ad)-B, Sc2C2@C84(Ad)-C, and Sc2C2@C84(Ad)-D). The structure of Sc2C2@C84(Ad)-C was characterized using X-ray crystallography. Thermal interconversion of Sc2C2@C84(Ad)-A and Sc2C2@C84(Ad)-B to Sc2C2@C84(Ad)-C was also observed. The reaction mechanisms of the Ad addition and thermal interconversion were elucidated from theoretical calculations. Calculation results suggest that C84(Ad)-B and Sc2C2@C84(Ad)-C are thermodynamically favorable products. Their different chemical reactivities derive from Sc2C2 doping, which raises the HOMO and LUMO levels of the D2d(23)-C84 carbon cage.

Novel biogenic aggregation of moss gemmae on a disappearing African glacier.

Tropical regions are not well represented in glacier biology, yet many tropical glaciers are under threat of disappearance due to climate change. Here we report a novel biogenic aggregation at the terminus of a glacier in the Rwenzori Mountains, Uganda. The material was formed by uniseriate protonemal moss gemmae and protonema. Molecular analysis of five genetic markers determined the taxon as Ceratodon purpureus, a cosmopolitan species that is widespread in tropical to polar region. Given optimal growing temperatures of isolate is 20-30 °C, the cold glacier surface might seem unsuitable for this species. However, the cluster of protonema growth reached approximately 10 °C in daytime, suggesting that diurnal increase in temperature may contribute to the moss's ability to inhabit the glacier surface. The aggregation is also a habitat for microorganisms, and the disappearance of this glacier will lead to the loss of this unique ecosystem.

Utilizing the effective xanthophyll cycle for blooming of Ochromonas smithii and O. itoi (Chrysophyceae) on the snow surface.

Snow algae inhabit unique environments such as alpine and high latitudes, and can grow and bloom with visualizing on snow or glacier during spring-summer. The chrysophytes Ochromonas smithii and Ochromonas itoi are dominant in yellow-colored snow patches in mountainous heavy snow areas from late May to early June. It is considered to be effective utilizing the xanthophyll cycle and holding sunscreen pigments as protective system for snow algae blooming in the vulnerable environment such as low temperature and nutrients, and strong light, however the study on the photoprotection of chrysophytes snow algae has not been shown. To dissolve how the chrysophytes snow algae can grow and bloom under such an extreme environment, we studied with the object of light which is one point of significance to this problem. We collected the yellow snows and measured photosynthetically active radiation at Mt. Gassan in May 2008 when the bloom occurred, then tried to establish unialgal cultures of O. smithii and O. itoi, and examined their photosynthetic properties by a PAM chlorophyll fluorometer and analyzed the pigment compositions before and after illumination with high-light intensities to investigate the working xanthophyll cycle. This experimental study using unialgal cultures revealed that both O. smithii and O. itoi utilize only the efficient violaxanthin cycle for photoprotection as a dissipation system of surplus energy under prolonged high-light stress, although they possess chlorophyll c with diadinoxanthin.

Sympathetic neural regulation of heart rate is robust against high plasma catecholamines.

The sympathetic regulation of heart rate (HR) may be attained by neural and humoral factors. With respect to the humoral factor, plasma noradrenaline (NA) and adrenaline (Adr) can reportedly increase to levels approximately 10 times higher than resting level during severe exercise. Whether such high plasma NA or Adr interfered with the sympathetic neural regulation of HR remained unknown. We estimated the transfer function from cardiac sympathetic nerve stimulation (SNS) to HR in anesthetized and vagotomized rabbits. An intravenous administration of NA (n = 6) at 1 and 10 microg.kg(-1).h(-1) increased plasma NA concentration (pg/ml) from a baseline level of 438 +/- 117 (mean +/- SE) to 974 +/- 106 and 6,830 +/- 917 (P < 0.01), respectively. The dynamic gain (bpm/Hz) of the transfer function did not change significantly (from 7.6 +/- 1.2 to 7.5 +/- 1.1 and 8.1 +/- 1.1), whereas mean HR (in bpm) during SNS slightly increased from 280 +/- 24 to 289 +/- 22 (P < 0.01) and 288 +/- 22 (P < 0.01). The intravenous administration of Adr (n = 6) at 1 and 10 microg.kg(-1).h(-1) increased plasma Adr concentration (pg/ml) from a baseline level of 257 +/- 86 to 659 +/- 172 and 2,760 +/- 590 (P < 0.01), respectively. Neither the dynamic gain (from 8.0 +/- 0.6 to 8.4 +/- 0.8 and 8.2 +/- 1.0) nor the mean HR during SNS (from 274 +/- 13 to 275 +/- 13 and 274 +/- 13) changed significantly. In contrast, the intravenous administration of isoproterenol (n = 6) at 10 microg.kg(-1).h(-1) significantly increased mean HR during SNS (from 278 +/- 11 to 293 +/- 9, P < 0.01) and blunted the transfer gain value at 0.0078 Hz (from 5.9 +/- 1.0 to 1.0 +/- 0.4, P < 0.01). In conclusion, high plasma NA or Adr hardly affected the dynamic sympathetic neural regulation of HR.

Stepwise molding of a highly selective ribonucleopeptide receptor.

The structural characteristics of RNA-peptide (RNP) complexes are suitable for molding of a ligand-binding pocket of the RNP complex in a stepwise manner. The first step involves molding of the RNA subunit by in vitro selection of an RNP pool originating from an RNA library and the peptide, as previously reported for the construction of an ATP-binding RNP complex from an RRE RNA-Rev peptide complex. The second step involves selection from an RNP library consisting of Rev peptides with randomized amino acid residues and the RNA subunit selected in the first molding. The ATP-binding pocket produced by sequential molding of RNA and peptide subunits shows higher affinity to ATP and a distinct specificity for ATP versus dATP as compared to the ATP-binding RNP receptor in which only the RNA subunit has been molded. The second step selection from the peptide-based RNP library allows expansion of the ATP recognition surface, consisting of both RNA and peptide subunits, to enhance the affinity and selectivity to discriminate ATP against dATP. Our approach of stepwise molding offers the advantage of increasing the diversity of the RNP library by utilizing characteristics of different biopolymers. The ribonucleopeptide-based, multi-subunit approach is also extendable to other biomacromolecular assemblies, which may yield artificial receptors and enzymes with increased specificity and more diverse chemical activities.

Stepwise functionalization of ribonucleopeptide complexes to receptors and sensors.

We describe here stepwise functionalization strategies of ribonucleopeptide complexes to receptors and sensors. A structurally well-defined complex of RNA and peptide (ribonucleopeptide: RNP) was constructed by a structure-based design. The first step optimizes an ATP-binding characteristic of an RNP receptor based on an in vitro selection of an RNP library generated by introducing randomized nucleotide sequences in the RNA subunit. In the second step, the RNP receptor from the first step was functionalized to an RNP receptor for nicotinamide adenine dinucleotide (NAD+) or to ATP sensors by using respective modifications of the peptide subunit.

Design of sensing ribonucleopeptides for small ligands.

Here we report a simple method to convert synthetic receptors to fluorescent sensors. An RNA-peptide complex (ribonucleopeptide) with a known three-dimensional structure is used as a framework of the receptor. Artificial ribonucleopeptide sensors were created with a combination of in vitro selection method and successive modification of the peptide with a fluorophore. A ribonucleopeptide complex of the fluorophore labeled peptide showed a remarkable fluorescence emission change upon binding cognate ligands.