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Sarmento H.,CSIC - Institute of Marine Sciences | Sarmento H.,Federal University of São Carlos | Casamayor E.O.,Integrative Freshwater Ecology Group | Auguet J.-C.,Integrative Freshwater Ecology Group | And 7 more authors.
Frontiers in Microbiology | Year: 2015

Sharp boundaries in the physical environment are usually associated with abrupt shifts in organism abundance, activity, and diversity. Aquatic surface microlayers (SML) form a steep gradient between two contrasted environments, the atmosphere and surface waters, where they regulate the gas exchange between both environments. They usually harbor an abundant and active microbial life: the neuston. Few ecosystems are subjected to such a high UVR regime as high altitude lakes during summer. Here, we measured bulk estimates of heterotrophic activity, community structure and single-cell physiological properties by flow cytometry in 19 high-altitude remote Pyrenean lakes and compared the biological processes in the SML with those in the underlying surface waters. Phototrophic picoplankton (PPP) populations, were generally present in high abundances and in those lakes containing PPP populations with phycoerythrin (PE), total PPP abundance was higher at the SML. Heterotrophic nanoflagellates (HNF) were also more abundant in the SML. Bacteria in the SML had lower leucine incorporation rates, lower percentages of "live" cells, and higher numbers of highly-respiring cells, likely resulting in a lower growth efficiency. No simple and direct linear relationships could be found between microbial abundances or activities and environmental variables, but factor analysis revealed that, despite their physical proximity, microbial life in SML and underlying waters was governed by different and independent processes. Overall, we demonstrate that piconeuston in high altitude lakes has specific features different from those of the picoplankton, and that they are highly affected by potential stressful environmental factors, such as high UVR radiation. © 2015 Sarmento, Casamayor, Auguet, Vila-Costa, Felip, Camarero and Gasol.


PubMed | Integrative Freshwater Ecology Group, Federal University of São Carlos, University of Lleida and CSIC - Institute of Marine Sciences
Type: | Journal: Frontiers in microbiology | Year: 2015

Sharp boundaries in the physical environment are usually associated with abrupt shifts in organism abundance, activity, and diversity. Aquatic surface microlayers (SML) form a steep gradient between two contrasted environments, the atmosphere and surface waters, where they regulate the gas exchange between both environments. They usually harbor an abundant and active microbial life: the neuston. Few ecosystems are subjected to such a high UVR regime as high altitude lakes during summer. Here, we measured bulk estimates of heterotrophic activity, community structure and single-cell physiological properties by flow cytometry in 19 high-altitude remote Pyrenean lakes and compared the biological processes in the SML with those in the underlying surface waters. Phototrophic picoplankton (PPP) populations, were generally present in high abundances and in those lakes containing PPP populations with phycoerythrin (PE), total PPP abundance was higher at the SML. Heterotrophic nanoflagellates (HNF) were also more abundant in the SML. Bacteria in the SML had lower leucine incorporation rates, lower percentages of live cells, and higher numbers of highly-respiring cells, likely resulting in a lower growth efficiency. No simple and direct linear relationships could be found between microbial abundances or activities and environmental variables, but factor analysis revealed that, despite their physical proximity, microbial life in SML and underlying waters was governed by different and independent processes. Overall, we demonstrate that piconeuston in high altitude lakes has specific features different from those of the picoplankton, and that they are highly affected by potential stressful environmental factors, such as high UVR radiation.


PubMed | University of the Basque Country, Catalan Institute for Water Research, Integrative Freshwater Ecology Group, Eawag - Swiss Federal Institute of Aquatic Science and Technology and University of Aberdeen
Type: Journal Article | Journal: Ecology | Year: 2016

Stream microbial communities and associated processes are influenced by environmental fluctuations that may ultimately dictate nutrient export. Discharge fluctuations caused by intermittent stream flow are increasing worldwide in response to global change. We examined the impact of flow cessation and drying on in-stream nitrogen cycling. We determined archaeal (AOA) and bacterial ammonia oxidizer (AOB) abundance and ammonia oxidation activity in surface and deep sediments from different sites along the Fuirosos stream (Spain) subjected to contrasting hydrological conditions (i.e., running water, isolated pools, and dry streambeds). AOA were more abundant than AOB, with no major changes across hydrological conditions or sediment layers. However, ammonia oxidation activity and sediment nitrate content increased with the degree of stream drying, especially in surface sediments. Upscaling of our results shows that ammonia oxidation in dry streambeds can contribute considerably (~50%) to the high nitrate export typically observed in intermittent streams during first-flush events following flow reconnection. Our study illustrates how the dry channels of intermittent streams can be potential hotspots of ammonia oxidation. Consequently, shifts in the duration, spatial extent and severity of intermittent flow can play a decisive role in shaping nitrogen cycling and export along fluvial networks in response to global change.


Peipoch M.,Integrative Freshwater Ecology Group | Gacia E.,Integrative Freshwater Ecology Group | Blesa A.,Autonomous University of Madrid | Ribot M.,Integrative Freshwater Ecology Group | And 2 more authors.
Aquatic Sciences | Year: 2014

We examined the relevance of dissolved inorganic nitrogen (DIN) forms (nitrate and ammonium) in stream water as N sources for different macrophyte species. To do this, we investigated the variability and relationships between 15N natural abundance of DIN forms and of four different macrophyte species in five different streams influenced by inputs from wastewater treatment plants and over time within one of these streams. Results showed that 15N signatures were similar in species of submersed and amphibious macrophytes and in stream water DIN, whereas 15N signatures of the riparian species were not. 15N signatures of macrophytes were generally closer to 15N signatures of nitrate, regardless of the species considered. Our results showed significant relationships between 15N signatures of DIN and those of submersed Callitriche stagnalis and amphibious Veronica beccabunga and Apium nodiflorum, suggesting stream water DIN as a relevant N source for these two functional groups. Moreover, results from a mixing model suggested that stream water DIN taken up by the submersed and amphibious species was mostly in the form of nitrate. Together, these results suggest different contribution to in-stream N uptake among the spatially-segregated species of macrophytes. While submersed and amphibious species can contribute to in-stream N uptake by assimilation of DIN, macrophyte species located at stream channel edges do not seem to rely on stream water DIN as an N source. Ultimately, these results add a functional dimension to the current use of macrophytes for the restoration of stream channel morphology, indicating that they can also contribute to reduce excess DIN in streams. © 2013 Springer Basel.


PubMed | J. Craig Venter Institute, Integrative Freshwater Ecology Group and Catalan Institute for Water Research
Type: Journal Article | Journal: Microbial ecology | Year: 2016

Microbial communities growing under extreme low redox conditions are present in anoxic and sulfide-rich (euxinic) environments such as karstic lakes and experience limitation of electron acceptors. The fine natural chemical gradients and the large diversity of organic and inorganic compounds accumulated in bottom waters are impossible to mimic under laboratory conditions, and only a few groups have been cultured. We investigated the bacterial composition in the oxic-anoxic interface and in the deep waters of three sulfurous lakes from the Lake Banyoles karstic area (NE Spain) through 16S rRNA gene tag sequencing and identified the closest GenBank counterpart. High diversity indices were found in most of the samples with >15 phyla/classes and >45 bacterial orders. A higher proportion of operational taxonomic units (OTUs) of the highest novelty was found in the hypolimnia (38 % of total sequences) than in the metalimnia (17 %), whereas the percentage of OTUs closer to cultured counterparts (i.e., 97 % identity in the 16S rRNA gene) was 6 to 21 %, respectively. Elusimicrobia, Chloroflexi, Fibrobacteres, and Spirochaetes were the taxa with the highest proportion of novel sequences. Interestingly, tag sequencing results comparison with metagenomics data available from the same dataset, showed a systematic underestimation of sulfur-oxidizing Epsilonproteobacteria with the currently available 907R universal primer. Overall, despite the limitation of electron acceptors, a highly diverse and novel assemblage was present in dark and euxinic hypolimnetic freshwaters, unveiling a hotspot of microbial diversity with a remarkable gap with cultured counterparts.


PubMed | University of Girona, Integrative Freshwater Ecology Group, Free University of Colombia, University of Southern Denmark and 3 more.
Type: | Journal: Scientific reports | Year: 2015

Iron-rich (ferruginous) ocean chemistry prevailed throughout most of Earths early history. Before the evolution and proliferation of oxygenic photosynthesis, biological production in the ferruginous oceans was likely driven by photoferrotrophic bacteria that oxidize ferrous iron {Fe(II)} to harness energy from sunlight, and fix inorganic carbon into biomass. Photoferrotrophs may thus have fuelled Earths early biosphere providing energy to drive microbial growth and evolution over billions of years. Yet, photoferrotrophic activity has remained largely elusive on the modern Earth, leaving models for early biological production untested and imperative ecological context for the evolution of life missing. Here, we show that an active community of pelagic photoferrotrophs comprises up to 30% of the total microbial community in illuminated ferruginous waters of Kabuno Bay (KB), East Africa (DR Congo). These photoferrotrophs produce oxidized iron {Fe(III)} and biomass, and support a diverse pelagic microbial community including heterotrophic Fe(III)-reducers, sulfate reducers, fermenters and methanogens. At modest light levels, rates of photoferrotrophy in KB exceed those predicted for early Earth primary production, and are sufficient to generate Earths largest sedimentary iron ore deposits. Fe cycling, however, is efficient, and complex microbial community interactions likely regulate Fe(III) and organic matter export from the photic zone.


PubMed | Integrative Freshwater Ecology Group, CNRS Center for Marine Biodiversity, Exploitation and Conservation and University of Girona
Type: Journal Article | Journal: The ISME journal | Year: 2016

Members of the archaeal Miscellaneous Crenarchaeotic Group (MCG) are among the most successful microorganisms on the planet. During its evolutionary diversification, this very diverse group has managed to cross the saline-freshwater boundary, one of the most important evolutionary barriers structuring microbial communities. However, the current understanding on the ecological significance of MCG in freshwater habitats is scarce and the evolutionary relationships between freshwater and saline MCG remains poorly known. Here, we carried out molecular phylogenies using publicly available 16S rRNA gene sequences from various geographic locations to investigate the distribution of MCG in freshwater and saline sediments and to evaluate the implications of saline-freshwater transitions during the diversification events. Our approach provided a robust ecological framework in which MCG archaea appeared as a core generalist group in the sediment realm. However, the analysis of the complex intragroup phylogeny of the 21 subgroups currently forming the MCG lineage revealed that distinct evolutionary MCG subgroups have arisen in marine and freshwater sediments suggesting the occurrence of adaptive evolution specific to each habitat. The ancestral state reconstruction analysis indicated that this segregation was mainly due to the occurrence of a few saline-freshwater transition events during the MCG diversification. In addition, a network analysis showed that both saline and freshwater MCG recurrently co-occur with archaea of the class Thermoplasmata in sediment ecosystems, suggesting a potentially relevant trophic connection between the two clades.


Liarte S.,University of Murcia | Ubero-Pascal N.,University of Murcia | Garcia-Ayala A.,University of Murcia | Puig M.-A.,Integrative Freshwater Ecology Group
Toxicon | Year: 2014

The ability of microcystins (MCs), the main group of cyanotoxins, to affect the physiological processes and tissues of insects has received little attention. Fresh water dissolved MCs represent one of the main sources of cyanotoxins. In the experiment described herein, captured wild mayfly Ecdyonurus angelieri Thomas, 1968 larvae were exposed to 5 ppb of two distinct microcystins, MC-LR and MC-LW, in separate assays. Evidence of induced mortality, MCs bioaccumulation and severe histological damage affecting fat body and alterations in the tracheal system were evident. Our results reveal the acute sensitivity of the mayfly E. angelieri to MCS, which may serve as early indicators or cyanotoxins production and the quality of freshwater streams. © 2014 Elsevier Ltd. All rights reserved.


PubMed | Integrative Freshwater Ecology Group and University of Murcia
Type: | Journal: Toxicon : official journal of the International Society on Toxinology | Year: 2014

The ability of microcystins (MCs), the main group of cyanotoxins, to affect the physiological processes and tissues of insects has received little attention. Fresh water dissolved MCs represent one of the main sources of cyanotoxins. In the experiment described herein, captured wild mayfly Ecdyonurus angelieri Thomas, 1968 larvae were exposed to 5ppb of two distinct microcystins, MC-LR and MC-LW, in separate assays. Evidence of induced mortality, MCs bioaccumulation and severe histological damage affecting fat body and alterations in the tracheal system were evident. Our results reveal the acute sensitivity of the mayfly E. angelieri to MCS, which may serve as early indicators or cyanotoxins production and the quality of freshwater streams.


A natural planktonic bloom of a brown-pigmented photosynthetic green sulfur bacteria (GSB) from the disphotic zone of karstic Lake Banyoles (NE Spain) was studied as a natural enrichment culture from which a nearly complete genome was obtained after metagenomic assembly. We showed in situ a case where horizontal gene transfer (HGT) explained the ecological success of a natural population unveiling ecosystem-specific adaptations. The uncultured brown-pigmented GSB was 99.7% identical in the 16S rRNA gene sequence to its green-pigmented cultured counterpart Chlorobium luteolum DSM 273T. Several differences were detected for ferrous iron acquisition potential, ATP synthesis and gas vesicle formation, although the most striking trait was related to pigment biosynthesis strategy. Chl. luteolum DSM 273T synthesizes bacteriochlorophyll (BChl) c, whereas Chl. luteolum CIII incorporated by HGT a 18-kbp cluster with the genes needed for BChl e and specific carotenoids biosynthesis that provided ecophysiological advantages to successfully colonize the dimly lit waters. We also genomically characterized what we believe to be the first described GSB phage, which based on the metagenomic coverage was likely in an active state of lytic infection. Overall, we observed spread HGT and we unveiled clear evidence for virus-mediated HGT in a natural population of photosynthetic GSB.The ISME Journal advance online publication, 8 July 2016; doi:10.1038/ismej.2016.93. © 2016 International Society for Microbial Ecology

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