TY - JOUR A1 - Ghylin, Trevor W. A1 - Garcia, Sarahi L. A1 - Moya, Francisco A1 - Oyserman, Ben O. A1 - Schwientek, Patrick A1 - Forest, Katrina T. A1 - Mutschler, James A1 - Dwulit-Smith, Jeffrey A1 - Chan, Leong-Keat A1 - Martinez-Garcia, Manuel A1 - Sczyrba, Alexander A1 - Stepanauskas, Ramunas A1 - Grossart, Hans-Peter A1 - Woyke, Tanja A1 - Warnecke, Falk A1 - Malmstrom, Rex A1 - Bertilsson, Stefan A1 - McMahon, Katherine D. T1 - Comparative single-cell genomics reveals potential ecological niches for the freshwater acl Actinobacteria lineage JF - The ISME journal : multidisciplinary journal of microbial ecology N2 - Members of the acI lineage of Actinobacteria are the most abundant microorganisms in most freshwater lakes; however, our understanding of the keys to their success and their role in carbon and nutrient cycling in freshwater systems has been hampered by the lack of pure cultures and genomes. We obtained draft genome assemblies from 11 single cells representing three acI tribes (acI-A1, acI-A7, acI-B1) from four temperate lakes in the United States and Europe. Comparative analysis of acI SAGs and other available freshwater bacterial genomes showed that acI has more gene content directed toward carbohydrate acquisition as compared to Polynucleobacter and LD12 Alphaproteobacteria, which seem to specialize more on carboxylic acids. The acI genomes contain actinorhodopsin as well as some genes involved in anaplerotic carbon fixation indicating the capacity to supplement their known heterotrophic lifestyle. Genome-level differences between the acI-A and acI-B clades suggest specialization at the clade level for carbon substrate acquisition. Overall, the acI genomes appear to be highly streamlined versions of Actinobacteria that include some genes allowing it to take advantage of sunlight and N-rich organic compounds such as polyamines, di-and oligopeptides, branched-chain amino acids and cyanophycin. This work significantly expands the known metabolic potential of the cosmopolitan freshwater acI lineage and its ecological and genetic traits. Y1 - 2014 U6 - https://doi.org/10.1038/ismej.2014.135 SN - 1751-7362 SN - 1751-7370 VL - 8 IS - 12 SP - 2503 EP - 2516 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Leunert, Franziska A1 - Eckert, Werner A1 - Paul, Andrea A1 - Gerhardt, Volkmar A1 - Grossart, Hans-Peter T1 - Phytoplankton response to UV-generated hydrogen peroxide from natural organic matter JF - Journal of plankton research N2 - In aquatic systems, natural organic matter (NOM) and in particular humic substances effectively absorb the ultraviolet (UV)/visible light spectrum of solar radiation and act as a photoprotective filter for organisms. Simultaneously, UV contributes to the generation of potentially harmful reactive oxygen species (ROS). Dose-response experiments were conducted on cyanobacteria and green algae with hydrogen peroxide (H2O2) as a long-lived representative of ROS. Delayed fluorescence (DF) decay kinetics was used as a non-invasive tool to follow changes of phytoplankton activity in real time. In order to investigate phototoxicity and photoprotection by NOM on phytoplankton, we exposed algae to UV-pre-irradiated NOM and direct UV excitation. Cyanobacteria responded to H2O2 concentrations as low as 10(-7) M, while green algae were 2 orders of magnitude less sensitive. UV irradiation of medium with NOM generated H2O2 concentrations of 1.5 x 10(-7) to 3.6 x 10(-7) M. When exposed to these concentrations, only the DF of cyanobacteria led to a measurable effect while that of green algae did not change. The addition of NOM protected all phytoplankton from direct UV irradiation, but cyanobacteria benefitted less. From this we conclude that UV-irradiated water enriched with NOM can adversely affect the physiology of cyanobacteria, but not of green algae, which might control phytoplankton composition and species-specific activities. KW - reactive oxygen species KW - Microcystis aeruginosa KW - green algae KW - delayed fluorescence KW - phycocyanin Y1 - 2014 U6 - https://doi.org/10.1093/plankt/fbt096 SN - 0142-7873 SN - 1464-3774 VL - 36 IS - 1 SP - 185 EP - 197 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Tada, Yuya A1 - Grossart, Hans-Peter T1 - Community shifts of actively growing lake bacteria after N-acetyl-glucosamine addition: improving the BrdU-FACS method JF - The ISME journal : multidisciplinary journal of microbial ecology N2 - In aquatic environments, community dynamics of bacteria, especially actively growing bacteria (AGB), are tightly linked with dissolved organic matter (DOM) quantity and quality. We analyzed the community dynamics of DNA-synthesizing and accordingly AGB by linking an improved bromodeoxyuridine immunocytochemistry approach with fluorescence-activated cell sorting (BrdU-FACS). FACS-sorted cells of even oligotrophic ecosystems in winter were characterized by 16S rRNA gene analysis. In incubation experiments, we examined community shifts of AGB in response to the addition of N-acetyl-glucosamine (NAG), one of the most abundant aminosugars in aquatic systems. Our improved BrdU-FACS analysis revealed that AGB winter communities of oligotrophic Lake Stechlin (northeastern Germany) substantially differ from those of total bacteria and consist of Alpha-, Beta-, Gamma-, Deltaproteobacteria, Actinobacteria, Candidatus OP10 and Chloroflexi. AGB populations with different BrdU-fluorescence intensities and cell sizes represented different phylotypes suggesting that single-cell growth potential varies at the taxon level. NAG incubation experiments demonstrated that a variety of widespread taxa related to Alpha-, Beta-, Gammaproteobacteria, Bacteroidetes, Actinobacteria, Firmicutes, Planctomycetes, Spirochaetes, Verrucomicrobia and Chloroflexi actively grow in the presence of NAG. The BrdU-FACS approach enables detailed phylogenetic studies of AGB and, thus, to identify those phylotypes which are potential key players in aquatic DOM cycling. KW - actively growing bacteria (AGB) KW - bromodeoxyuridine (BrdU) immunocytochemistry KW - fluorescence-activated cell sorting (FACS) KW - bacterial community composition KW - N-acetyl-glucosamine (NAG) KW - Lake Stechlin Y1 - 2014 U6 - https://doi.org/10.1038/ismej.2013.148 SN - 1751-7362 SN - 1751-7370 VL - 8 IS - 2 SP - 441 EP - 454 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Tang, Kam W. A1 - McGinnis, Daniel F. A1 - Frindte, Katharina A1 - Bruchert, Volker A1 - Grossart, Hans-Peter T1 - Paradox reconsidered: Methane oversaturation in well-oxygenated lake waters JF - Limnology and oceanography N2 - The widely reported paradox of methane oversaturation in oxygenated water challenges the prevailing paradigm that microbial methanogenesis only occurs under anoxic conditions. Using a combination of field sampling, incubation experiments, and modeling, we show that the recurring mid-water methane peak in Lake Stechlin, northeast Germany, was not dependent on methane input from the littoral zone or bottom sediment or on the presence of known micro-anoxic zones. The methane peak repeatedly overlapped with oxygen oversaturation in the seasonal thermocline. Incubation experiments and isotope analysis indicated active methane production, which was likely linked to photosynthesis and/or nitrogen fixation within the oxygenated water, whereas lessening of methane oxidation by light allowed accumulation of methane in the oxygen-rich upper layer. Estimated methane efflux from the surface water was up to 5 mmol m(-2) d(-1). Mid-water methane oversaturation was also observed in nine other lakes that collectively showed a strongly negative gradient of methane concentration within 0-20% dissolved oxygen (DO) in the bottom water, and a positive gradient within >= 20% DO in the upper water column. Further investigation into the responsible organisms and biochemical pathways will help improve our understanding of the global methane cycle. Y1 - 2014 U6 - https://doi.org/10.4319/lo.2014.59.1.0275 SN - 0024-3590 SN - 1939-5590 VL - 59 IS - 1 SP - 275 EP - 284 PB - Wiley CY - Waco ER - TY - JOUR A1 - Hartman, Jan F. A1 - Gentz, Torben A1 - Schiller, Amanda A1 - Greule, Markus A1 - Grossart, Hans-Peter A1 - Ionescu, Danny A1 - Keppler, Frank A1 - Martinez-Cruz, Karla A1 - Sepulveda-Jauregui, Armando A1 - Isenbeck-Schroeter, Margot T1 - A f ast and sensitive method for the continuous in situ determination of dissolved methane and its delta C-13-isotope ratio in surface waters JF - Limnology and Oceanography-methods N2 - A fast and sensitive method for the continuous determination of methane (CH4) and its stable carbon isotopic values (delta C-13-CH4) in surface waters was developed by applying a vacuum to a gas/liquid exchange membrane and measuring the extracted gases by a portable cavity ring-down spectroscopy analyser (M-CRDS). The M-CRDS was calibrated and characterized for CH4 concentration and delta C-13-CH4 with synthetic water standards. The detection limit of the M-CRDS for the simultaneous determination of CH4 and delta C-13-CH4 is 3.6 nmol L-1 CH4. A measurement precision of CH4 concentrations and delta C-13-CH4 in the range of 1.1%, respectively, 1.7 parts per thousand (1 sigma) and accuracy (1.3%, respectively, 0.8 parts per thousand [1 sigma]) was achieved for single measurements and averaging times of 10 min. The response time tau of 57 +/- 5 s allow determination of delta C-13-CH4 values more than twice as fast than other methods. The demonstrated M-CRDS method was applied and tested for Lake Stechlin (Germany) and compared with the headspace-gas chromatography and fast membrane CH4 concentration methods. Maximum CH4 concentrations (577 nmol L-1) and lightest delta C-13-CH4 (-35.2 parts per thousand) were found around the thermocline in depth profile measurements. The M-CRDS-method was in good agreement with other methods. Temporal variations in CH4 concentration and delta C-13-CH4 obtained in 24 h measurements indicate either local methane production/oxidation or physical variations in the thermocline. Therefore, these results illustrate the need of fast and sensitive analyses to achieve a better understanding of different mechanisms and pathways of CH4 formation in aquatic environments. Y1 - 2018 U6 - https://doi.org/10.1002/lom3.10244 SN - 1541-5856 VL - 16 IS - 5 SP - 273 EP - 285 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Leach, Taylor H. A1 - Beisner, Beatrix E. A1 - Carey, Cayelan C. A1 - Pernica, Patricia A1 - Rose, Kevin C. A1 - Huot, Yannick A1 - Brentrup, Jennifer A. A1 - Domaizon, Isabelle A1 - Grossart, Hans-Peter A1 - Ibelings, Bastiaan W. A1 - Jacquet, Stephan A1 - Kelly, Patrick T. A1 - Rusak, James A. A1 - Stockwell, Jason D. A1 - Straile, Dietmar A1 - Verburg, Piet T1 - Patterns and drivers of deep chlorophyll maxima structure in 100 lakes BT - the relative importance of light and thermal stratification JF - Limnology and oceanography N2 - The vertical distribution of chlorophyll in stratified lakes and reservoirs frequently exhibits a maximum peak deep in the water column, referred to as the deep chlorophyll maximum (DCM). DCMs are ecologically important hot spots of primary production and nutrient cycling, and their location can determine vertical habitat gradients for primary consumers. Consequently, the drivers of DCM structure regulate many characteristics of aquatic food webs and biogeochemistry. Previous studies have identified light and thermal stratification as important drivers of summer DCM depth, but their relative importance across a broad range of lakes is not well resolved. We analyzed profiles of chlorophyll fluorescence, temperature, and light during summer stratification from 100 lakes in the Global Lake Ecological Observatory Network (GLEON) and quantified two characteristics of DCM structure: depth and thickness. While DCMs do form in oligotrophic lakes, we found that they can also form in eutrophic to dystrophic lakes. Using a random forest algorithm, we assessed the relative importance of variables associated with light attenuation vs. thermal stratification for predicting DCM structure in lakes that spanned broad gradients of morphometry and transparency. Our analyses revealed that light attenuation was a more important predictor of DCM depth than thermal stratification and that DCMs deepen with increasing lake clarity. DCM thickness was best predicted by lake size with larger lakes having thicker DCMs. Additionally, our analysis demonstrates that the relative importance of light and thermal stratification on DCM structure is not uniform across a diversity of lake types. Y1 - 2018 U6 - https://doi.org/10.1002/lno.10656 SN - 0024-3590 SN - 1939-5590 VL - 63 IS - 2 SP - 628 EP - 646 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Beisner, Beatrix E. A1 - Grossart, Hans-Peter A1 - Gasol, Josep M. T1 - A guide to methods for estimating phago-mixotrophy in nanophytoplankton JF - Journal of plankton research N2 - Growing attention to phytoplankton mixotrophy as a trophic strategy has led to significant revisions of traditional pelagic food web models and ecosystem functioning. Although some empirical estimates of mixotrophy do exist, a much broader set of in situ measurements are required to (i) identify which organisms are acting as mixotrophs in real time and to (ii) assess the contribution of their heterotrophy to biogeochemical cycling. Estimates are needed through time and across space to evaluate which environmental conditions or habitats favour mixotrophy: conditions still largely unknown. We review methodologies currently available to plankton ecologists to undertake estimates of plankton mixotrophy, in particular nanophytoplankton phago-mixotrophy. Methods are based largely on fluorescent or isotopic tracers, but also take advantage of genomics to identify phylotypes and function. We also suggest novel methods on the cusp of use for phago-mixotrophy assessment, including single-cell measurements improving our capacity to estimate mixotrophic activity and rates in wild plankton communities down to the single-cell level. Future methods will benefit from advances in nanotechnology, micromanipulation and microscopy combined with stable isotope and genomic methodologies. Improved estimates of mixotrophy will enable more reliable models to predict changes in food web structure and biogeochemical flows in a rapidly changing world. KW - flow cytometry KW - phagotrophy KW - phytoplankton KW - methods KW - fluorescence KW - microscopy KW - FISH KW - isotopic methods KW - phylotypes KW - carbon flows KW - gene sequencing Y1 - 2019 U6 - https://doi.org/10.1093/plankt/fbz008 SN - 0142-7873 SN - 1464-3774 VL - 41 IS - 2 SP - 77 EP - 89 PB - Oxford Univ. Press CY - Oxford ER -