TY - JOUR A1 - Tittel, Joerg A1 - Wiehle, Ines A1 - Wannicke, Nicola A1 - Kampe, Heike A1 - Poerschmann, Juergen A1 - Meier, Jutta A1 - Kamjunke, Norbert T1 - Utilisation of terrestrial carbon by osmotrophic algae N2 - Terrestrial-derived dissolved organic carbon (DOC) contributes significantly to the energetic basis of many aquatic food webs. Although heterotrophic bacteria are generally considered to be the sole consumers of DOC, algae and cyanobacteria of various taxonomic groups are also capable of exploiting this resource. We tested the hypothesis that algae can utilise DOC in the presence of bacteria if organic resources are supplied in intervals by photolysis of recalcitrant DOC. In short-term uptake experiments, we changed irradiation in the range of minutes. As model substrates, polymers of radiolabelled coumaric acid (PCA) were used, which during photolysis are known to release aromatic compounds comparable to terrestrial-derived and refractory DOC. Three cultured freshwater algae readily assimilated PCA photoproducts equivalent to a biomass-specific uptake of 5-60% of the bacterial competitors present. Algal substrate acquisition did not depend on whether PCA was photolysed continuously or in intervals. However, the data show that photoproducts of terrestrial DOC can be a significant resource for osmotrophic algae. In long-term growth experiments, interval light was applied one hour per day. We allowed cultured Chlamydomonas to compete for ambient DOC of low concentration. We found higher abundances of Chlamydomonas when cultures were irradiated intermittently rather than continuously. These data suggest that photolysis of DOC supports algal heterotrophy, and potentially facilitates growth, when light fluctuations are large, as during the diurnal light cycle. We concluded that osmotrophic algae can efficiently convert terrestrial carbon into the biomass of larger organisms of aquatic food webs. Y1 - 2009 UR - http://www.springerlink.com/content/101191 U6 - https://doi.org/10.1007/s00027-008-8121-2 SN - 1015-1621 ER - TY - INPR A1 - Wannicke, Nicola A1 - Endres, S. A1 - Engel, A. A1 - Grossart, Hans-Peter A1 - Nausch, M. A1 - Unger, J. A1 - Voss, Martin T1 - Response of nodularia spumigena to pCO(2) - Part 1: Growth, production and nitrogen cycling T2 - Biogeosciences N2 - Heterocystous cyanobacteria of the genus Nodularia form extensive blooms in the Baltic Sea and contribute substantially to the total annual primary production. Moreover, they dispense a large fraction of new nitrogen to the ecosystem when inorganic nitrogen concentration in summer is low. Thus, it is of ecological importance to know how Nodularia will react to future environmental changes, in particular to increasing carbon dioxide (CO2) concentrations and what consequences there might arise for cycling of organic matter in the Baltic Sea. Here, we determined carbon (C) and dinitrogen (N-2) fixation rates, growth, elemental stoichiometry of particulate organic matter and nitrogen turnover in batch cultures of the heterocystous cyanobacterium Nodularia spumigena under low (median 315 mu atm), mid (median 353 mu atm), and high (median 548 mu atm) CO2 concentrations. Our results demonstrate an overall stimulating effect of rising pCO(2) on C and N-2 fixation, as well as on cell growth. An increase in pCO(2) during incubation days 0 to 9 resulted in an elevation in growth rate by 84 +/- 38% (low vs. high pCO(2)) and 40 +/- 25% (mid vs. high pCO(2)), as well as in N-2 fixation by 93 +/- 35% and 38 +/- 1%, respectively. C uptake rates showed high standard deviations within treatments and in between sampling days. Nevertheless, C fixation in the high pCO(2) treatment was elevated compared to the other two treatments by 97% (high vs. low) and 44% (high vs. mid) at day 0 and day 3, but this effect diminished afterwards. Additionally, elevation in carbon to nitrogen and nitrogen to phosphorus ratios of the particulate biomass formed (POC : POP and PON : POP) was observed at high pCO(2). Our findings suggest that rising pCO(2) stimulates the growth of heterocystous diazotrophic cyanobacteria, in a similar way as reported for the non-heterocystous diazotroph Trichodesmium. Implications for biogeochemical cycling and food web dynamics, as well as ecological and socio-economical aspects in the Baltic Sea are discussed. Y1 - 2012 U6 - https://doi.org/10.5194/bg-9-2973-2012 SN - 1726-4170 VL - 9 IS - 8 SP - 2973 EP - 2988 PB - Copernicus CY - Göttingen ER - 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 -