TY - JOUR A1 - Wannicke, Nicola A1 - Frindte, Katharina A1 - Gust, Giselher A1 - Liskow, Iris A1 - Wacker, Alexander A1 - Meyer, Andreas A1 - Grossart, Hans-Peter T1 - Measuring bacterial activity and community composition at high hydrostatic pressure using a novel experimental approach: a pilot study JF - FEMS microbiology ecology N2 - In this pilot study, we describe a high-pressure incubation system allowing multiple subsampling of a pressurized culture without decompression. The system was tested using one piezophilic (Photobacterium profundum), one piezotolerant (Colwellia maris) bacterial strain and a decompressed sample from the Mediterranean deep sea (3044 m) determining bacterial community composition, protein production (BPP) and cell multiplication rates (BCM) up to 27 MPa. The results showed elevation of BPP at high pressure was by a factor of 1.5 +/- 1.4 and 3.9 +/- 2.3 for P. profundum and C. maris, respectively, compared to ambient-pressure treatments and by a factor of 6.9 +/- 3.8 fold in the field samples. In P. profundum and C. maris, BCM at high pressure was elevated (3.1 +/- 1.5 and 2.9 +/- 1.7 fold, respectively) compared to the ambient-pressure treatments. After 3 days of incubation at 27 MPa, the natural bacterial deep-sea community was dominated by one phylum of the genus Exiguobacterium, indicating the rapid selection of piezotolerant bacteria. In future studies, our novel incubation system could be part of an isopiestic pressure chain, allowing more accurate measurement of bacterial activity rates which is important both for modeling and for predicting the efficiency of the oceanic carbon pump. KW - hydrostatic pressure KW - pressure chamber KW - piezophilic bacteria KW - deep-sea bacterial community KW - bacterial production KW - stable isotopes KW - membrane fatty acids Y1 - 2015 U6 - https://doi.org/10.1093/femsec/fiv036 SN - 0168-6496 SN - 1574-6941 VL - 91 IS - 5 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Pieck, Angelika A1 - Herlemann, Daniel P. P. A1 - Juergens, Klaus A1 - Grossart, Hans-Peter T1 - Particle-Associated Differ from Free-Living Bacteria in Surface Waters of the Baltic Sea JF - Frontiers in microbiology N2 - Many studies on bacterial community composition (BCC) do not distinguish between particle associated (PA) and free-living (FL) bacteria or neglect the PA fraction by pre-filtration removing most particles. Although temporal and spatial gradients in environmental variables are known to shape BCC, it remains unclear how and to what extent PA and FL bacterial diversity responds to such environmental changes. To elucidate the BCC of both bacterial fractions related to different environmental settings, we studied surface samples of three Baltic Sea stations (marine, mesohaline, and oligohaline) in two different seasons (summer and fall/winter). Amplicon sequencing of the 16S rRNA gene revealed significant differences in BCC of both bacterial fractions among stations and seasons, with a particularly high number of PA operational taxonomic units (OTUs at genus-level) at the marine station in both seasons. "Shannon and Simpson indices" showed a higher diversity of PA than FL bacteria at the marine station in both seasons and at the oligohaline station in fall/winter. In general, a high fraction of bacterial OTUs was found exclusively in the PA fraction (52% of total OTUs). These findings indicate that PA bacteria significantly contribute to overall bacterial richness and that they differ from FL bacteria. Therefore, to gain a deeper understanding on diversity and dynamics of aquatic bacteria, PA and FL bacteria should be generally studied independently. KW - microbial communities KW - microbial diversity KW - particle-associated and free-living bacteria KW - Baltic Sea KW - salinity gradient KW - seasons KW - 454-pyrosequencing Y1 - 2015 U6 - https://doi.org/10.3389/fmicb.2015.01297 SN - 1664-302X VL - 6 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Ishida, Seiji A1 - Nozaki, Daiki A1 - Grossart, Hans-Peter A1 - Kagami, Maiko T1 - Novel basal, fungal lineages from freshwater phytoplankton and lake samples JF - Environmental microbiology reports N2 - Zoosporic fungal parasites are known to control the extent and development of blooms of numerous phytoplankton species. Despite the obvious importance of ecological interactions between parasitic fungi and their phytoplanktonic hosts, their diversity remains largely unknown due to methodological limitations. Here, a method to genetically analyse fungi directly from single, infected colonies of the phytoplanktonic host was applied to field samples of large diatom species from mesotrophic Lake Biwa and eutrophic Lake Inba, Japan. Although previous research on interaction between lacustrine fungi and large phytoplankton has mainly focused on the role of parasitic Chytridiomycota, our results revealed that fungi attached to large diatoms included not only members of Chytridiomycota, but also members of Aphelida, Cryptomycota and yeast. The fungi belonging to Chytridiomycota and Aphelida form novel, basal lineages. Environmental clone libraries also support the occurrence of these lineages in Japanese lakes. The presented method enables us to better characterize individual fungal specimens on phytoplankton, and thus facilitate and improve the investigation of ecological relationships between fungi and phytoplankton in aquatic ecosystems. Y1 - 2015 U6 - https://doi.org/10.1111/1758-2229.12268 SN - 1758-2229 VL - 7 IS - 3 SP - 435 EP - 441 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Ionescu, Danny A1 - Bizic-Ionescu, Mina A1 - Khalili, Arzhang A1 - Malekmohammadi, Reza A1 - Morad, Reza Mohammad A1 - de Beer, Dirk A1 - Grossart, Hans-Peter T1 - A new tool for long-term studies of POM-bacteria interactions: overcoming the century-old Bottle Effect JF - Scientific reports N2 - Downward fluxes of particulate organic matter (POM) are the major process for sequestering atmospheric CO2 into aquatic sediments for thousands of years. Budget calculations of the biological carbon pump are heavily based on the ratio between carbon export (sedimentation) and remineralization (release to the atmosphere). Current methodologies determine microbial dynamics on POM using closed vessels, which are strongly biased towards heterotrophy due to rapidly changing water chemistry (Bottle Effect). We developed a flow-through rolling tank for long term studies that continuously maintains POM at near in-situ conditions. There, bacterial communities resembled in-situ communities and greatly differed from those in the closed systems. The active particle-associated community in the flow-through system was stable for days, contrary to hours previously reported for closed incubations. In contrast to enhanced respiration rates, the decrease in photosynthetic rates on particles throughout the incubation was much slower in our system than in traditional ones. These results call for reevaluating experimentally-derived carbon fluxes estimated using traditional methods. Y1 - 2015 U6 - https://doi.org/10.1038/srep14706 SN - 2045-2322 VL - 5 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Glud, Ronnie N. A1 - Grossart, Hans-Peter A1 - Larsen, Morten A1 - Tang, Kam W. A1 - Arendt, Kristine E. A1 - Rysgaard, Soren A1 - Thamdrup, Bo A1 - Gissel Nielsen, Torkel T1 - Copepod carcasses as microbial hot spots for pelagic denitrification JF - Limnology and oceanography N2 - Copepods are exposed to a high non-predatory mortality and their decomposing carcasses act as microniches with intensified microbial activity. Sinking carcasses could thereby represent anoxic microenvironment sustaining anaerobic microbial pathways in otherwise oxic water columns. Using non-invasive O-2 imaging, we document that carcasses of Calanus finmarchicus had an anoxic interior even at fully air-saturated ambient O-2 level. The extent of anoxia gradually expanded with decreasing ambient O-2 levels. Concurrent microbial sampling showed the expression of nitrite reductase genes (nirS) in all investigated carcass samples and thereby documented the potential for microbial denitrification in carcasses. The nirS gene was occasionally expressed in live copepods, but not as consistently as in carcasses. Incubations of sinking carcasses in (15)NO3-amended seawater demonstrated denitrification, of which on average 34%+/- 17% (n=28) was sustained by nitrification. However, the activity was highly variable and was strongly dependent on the ambient O-2 levels. While denitrification was present even at air-saturation (302 mol L-1), the average carcass specific activity increased several orders of magnitude to approximate to 1 nmol d(-1) at 20% air-saturation (55 mol O-2 L-1) at an ambient temperature of 7 degrees C. Sinking carcasses of C. finmarchicus therefore represent hotspots of pelagic denitrification, but the quantitative importance as a sink for bioavailable nitrogen is strongly dependent on the ambient O-2 level. The importance of carcass associated denitrification could be highly significant in O-2 depleted environments such as Oxygen Minimum Zones (OMZ). Y1 - 2015 U6 - https://doi.org/10.1002/lno.10149 SN - 0024-3590 SN - 1939-5590 VL - 60 IS - 6 SP - 2026 EP - 2036 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Garcia, Sarahi L. A1 - Buck, Moritz A1 - McMahon, Katherine D. A1 - Grossart, Hans-Peter A1 - Eiler, Alexander A1 - Warnecke, Falk T1 - Auxotrophy and intrapopulation complementary in the "interactome' of a cultivated freshwater model community JF - Molecular ecology N2 - Microorganisms are usually studied either in highly complex natural communities or in isolation as monoclonal model populations that we manage to grow in the laboratory. Here, we uncover the biology of some of the most common and yet-uncultured bacteria in freshwater environments using a mixed culture from Lake Grosse Fuchskuhle. From a single shotgun metagenome of a freshwater mixed culture of low complexity, we recovered four high-quality metagenome-assembled genomes (MAGs) for metabolic reconstruction. This analysis revealed the metabolic interconnectedness and niche partitioning of these naturally dominant bacteria. In particular, vitamin- and amino acid biosynthetic pathways were distributed unequally with a member of Crenarchaeota most likely being the sole producer of vitamin B12 in the mixed culture. Using coverage-based partitioning of the genes recovered from a single MAG intrapopulation metabolic complementarity was revealed pointing to social' interactions for the common good of populations dominating freshwater plankton. As such, our MAGs highlight the power of mixed cultures to extract naturally occurring interactomes' and to overcome our inability to isolate and grow the microbes dominating in nature. KW - community KW - cultures KW - interactions KW - metagenomics KW - populations Y1 - 2015 U6 - https://doi.org/10.1111/mec.13319 SN - 0962-1083 SN - 1365-294X VL - 24 IS - 17 SP - 4449 EP - 4459 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Frindte, Katharina A1 - Allgaier, Martin A1 - Grossart, Hans-Peter A1 - Eckert, Werner T1 - Microbial response to experimentally controlled redox transitions at the sediment water interface JF - PLoS one N2 - The sediment-water interface of freshwater lakes is characterized by sharp chemical gradients, shaped by the interplay between physical, chemical and microbial processes. As dissolved oxygen is depleted in the uppermost sediment, the availability of alternative electron acceptors, e.g. nitrate and sulfate, becomes the limiting factor. We performed a time series experiment in a mesocosm to simulate the transition from aerobic to anaerobic conditions at the sediment-water interface. Our goal was to identify changes in the microbial activity due to redox transitions induced by successive depletion of available electron acceptors. Monitoring critical hydrochemical parameters in the overlying water in conjunction with a new sampling strategy for sediment bacteria enabled us to correlate redox changes in the water to shifts in the active microbial community and the expression of functional genes representing specific redox-dependent microbial processes. Our results show that during several transitions from oxic-heterotrophic condition to sulfate-reducing condition, nitrate-availability and the on-set of sulfate reduction strongly affected the corresponding functional gene expression. There was evidence of anaerobic methane oxidation with NOx. DGGE analysis revealed redox-related changes in microbial activity and expression of functional genes involved in sulfate and nitrite reduction, whereas methanogenesis and methanotrophy showed only minor changes during redox transitions. The combination of high-frequency chemical measurements and molecular methods provide new insights into the temporal dynamics of the interplay between microbial activity and specific redox transitions at the sediment-water interface. Y1 - 2015 U6 - https://doi.org/10.1371/journal.pone.0143428 SN - 1932-6203 VL - 10 IS - 11 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Dubovskaya, Olga P. A1 - Tang, Kam W. A1 - Gladyshev, Michail I. A1 - Kirillin, Georgiy A1 - Buseva, Zhanna A1 - Kasprzak, Peter A1 - Tolomeev, Aleksandr P. A1 - Grossart, Hans-Peter T1 - Estimating In Situ Zooplankton Non-Predation Mortality in an Oligo-Mesotrophic Lake from Sediment Trap Data: Caveats and Reality Check JF - PLoS one N2 - Background Mortality is a main driver in zooplankton population biology but it is poorly constrained in models that describe zooplankton population dynamics, food web interactions and nutrient dynamics. Mortality due to non-predation factors is often ignored even though anecdotal evidence of non-predation mass mortality of zooplankton has been reported repeatedly. One way to estimate non-predation mortality rate is to measure the removal rate of carcasses, for which sinking is the primary removal mechanism especially in quiescent shallow water bodies. Objectives and Results We used sediment traps to quantify in situ carcass sinking velocity and non-predation mortality rate on eight consecutive days in 2013 for the cladoceran Bosmina longirostris in the oligo-mesotrophic Lake Stechlin; the outcomes were compared against estimates derived from in vitro carcass sinking velocity measurements and an empirical model correcting in vitro sinking velocity for turbulence resuspension and microbial decomposition of carcasses. Our results show that the latter two approaches produced unrealistically high mortality rates of 0.58-1.04 d(-1), whereas the sediment trap approach, when used properly, yielded a mortality rate estimate of 0.015 d(-1), which is more consistent with concurrent population abundance data and comparable to physiological death rate from the literature. Ecological implications Zooplankton carcasses may be exposed to water column microbes for days before entering the benthos; therefore, non-predation mortality affects not only zooplankton population dynamics but also microbial and benthic food webs. This would be particularly important for carbon and nitrogen cycles in systems where recurring mid-summer decline of zooplankton population due to non-predation mortality is observed. Y1 - 2015 U6 - https://doi.org/10.1371/journal.pone.0131431 SN - 1932-6203 VL - 10 IS - 7 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Corno, Gianluca A1 - Salka, Ivette A1 - Pohlmann, Kirsten A1 - Hall, Alex R. A1 - Grossart, Hans-Peter T1 - Interspecific interactions drive chitin and cellulose degradation by aquatic microorganisms JF - Aquatic microbial ecology : international journal N2 - Complex biopolymers (BPs) such as chitin and cellulose provide the majority of organic carbon in aquatic ecosystems, but the mechanisms by which communities of bacteria in natural systems exploit them are unclear. Previous degradation experiments in artificial systems predominantly used microcosms containing a single bacterial species, neglecting effects of interspecific interactions. By constructing simplified aquatic microbial communities, we tested how the addition of other bacterial species, of a nanoflagellate protist capable of consuming bacteria, or of both, affect utilization of BPs. Surprisingly, total abundance of resident bacteria in mixed communities increased upon addition of the protist. Concomitantly, bacteria shifted from free-living to aggregated morphotypes that seemed to promote utilization of BPs. In our model system, these interactions significantly increased productivity in terms of overall bacterial numbers and carbon transfer efficiency. This indicates that interactions on microbial aggregates may be crucial for chitin and cellulose degradation. We therefore suggest that interspecific microbial interactions must be considered when attempting to model the turnover of the vast pool of complex biopolymers in aquatic ecosystems. KW - Aggregation KW - Flagellate grazing KW - Ecological interactions KW - Microbial carbon transfer KW - Polymer degradation KW - System ecology Y1 - 2015 U6 - https://doi.org/10.3354/ame01765 SN - 0948-3055 SN - 1616-1564 VL - 76 IS - 1 SP - 27 EP - + PB - Institute of Mathematical Statistics CY - Oldendorf Luhe ER - TY - INPR A1 - Chattopadhyay, Madhab K. A1 - Chakraborty, Ranadhir A1 - Grossart, Hans-Peter A1 - Reddy, Gundlapally S. A1 - Jagannadham, Medicharla V. T1 - Antibiotic resistance of bacteria T2 - BioMed research international Y1 - 2015 U6 - https://doi.org/10.1155/2015/501658 SN - 2314-6133 SN - 2314-6141 PB - Hindawi Publishing Corp. CY - New York ER -