TY - BOOK A1 - Weithoff, Guntram T1 - Dietary restriction in two rotifers species : the effect of the length of food deprivation on life span and reproduction N2 - According to resource allocation theory, animals face a trade off between the allocation of resources into reproduction and into individual growth/maintenance. This trade off is reinforced when food conditions decline. It is well established in biological research that many animals increase their life span when food is in suboptimal supply for growth and/or reproduction. Such a situation of reduced food availability is called dietary restriction. An increase in life span under dietary restricted conditions is seen as a strategy to tolerate periods of food shortage so that the animals can start reproduction again when food is in greater supply. In this study, the effect of dietary restriction on life span and reproduction in two rotifer species, Cephalodella sp. and Elosa worallii, was investigated using life table experiments. The food concentration under dietary restricted conditions was below the threshold for population growth. It was (1) tested whether the rotifers start reproduction again after food replenishment, and (2) estimated whether the time scale of dietary restricted conditions is relevant for the persistence of a population in the field. Only E. worallii responded to dietary restriction with an increase in life span at the expense of reproduction. After replenishment of food, E. worallii started to reproduce again within I day. With an increase in the duration of dietary restricted conditions of up to 15 days, which is longer than the median life span of E. worallii under food saturation, the life span increased and the life time reproduction decreased. These results suggest that in a temporally (or spatially) variable environment, some rotifer populations can persist even during long periods of severe food deprivation. Y1 - 2007 UR - http://www.jstor.org/stable/40210866 U6 - https://doi.org/10.1007/s00442-007-0739-6 ER - TY - JOUR A1 - Tirok, Katrin A1 - Gaedke, Ursula T1 - Regulation of planktonic ciliate dynamics and functional composition during spring in Lake Constance N2 - Protozoans are among the most important grazers of phytoplankton and remineralizers of nutrients in marine and freshwater ecosystems, but less is known about the regulation of their population dynamics. We analyzed a 12 yr data set of ciliate biomass and species composition in large, deep Lake Constance to understand the factors influencing ciliate spring development. The start of ciliate net growth in spring was closely linked to that of edible algae, chlorophyll a and the vertical mixing intensity, but independent of water temperature. During ciliate spring growth, the relative contribution of ciliated interception feeders was positively related to that of cryptomonads, whereas the relative contribution of filter feeders correlated positively with that of non-cryptomonads. The duration of ciliate dominance in spring was largely controlled by the highly variable onset of the phytoplankton bloom, as the termination of the ciliate bloom was less variable. During years with an extended spring bloom of algae and ciliates, internally forced species shifts were observed in both communities. Interception feeders alternated with filter feeders in their relative importance as did cryptomonads and non-cryptomonads. Extended spring blooms were observed when vertical mixing intensity was low at low temperatures during early spring, which will become less likely under the anticipated climate change scenarios. The termination of the ciliate spring bloom occurred prior to a reduction in food concentration and mostly also prior to the mass development of daphnids alone, but coincided with increased grazing by various predators together, such as rotifers, copepods and daphnids in late May/early June. Y1 - 2007 UR - http://www.int-res.com/articles/ame2007/49/a049p087.pdf U6 - https://doi.org/10.3354/Ame01127 ER - TY - JOUR A1 - Tirok, Katrin A1 - Gaedke, Ursula T1 - The effect of irradiance, vertical mixing and temperature on spring phytoplankton dynamics under climate change : long-term observations and model analysis N2 - Spring algal development in deep temperate lakes is thought to be strongly influenced by surface irradiance, vertical mixing and temperature, all of which are expected to be altered by climate change. Based on long-term data from Lake Constance, we investigated the individual and combined effects of these variables on algal dynamics using descriptive statistics, multiple regression models and a processoriented dynamic simulation model. The latter considered edible and less-edible algae and was forced by observed or anticipated irradiance, temperature and vertical mixing intensity. Unexpectedly, irradiance often dominated algal net growth rather than vertical mixing for the following reason: algal dynamics depended on algal net losses from the euphotic layer to larger depth due to vertical mixing. These losses strongly depended on the vertical algal gradient which, in turn, was determined by the mixing intensity during the previous days, thereby introducing a memory effect. This observation implied that during intense mixing that had already reduced the vertical algal gradient, net losses due to mixing were small. Consequently, even in deep Lake Constance, the reduction in primary production due to low light was often more influential than the net losses due to mixing. In the regression model, the dynamics of small, fast-growing algae was best explained by vertical mixing intensity and global irradiance, whereas those of larger algae were best explained by their biomass 1 week earlier. The simulation model additionally revealed that even in late winter grazing may represent an important loss factor during calm periods when losses due to mixing are small. The importance of losses by mixing and grazing changed rapidly as it depended on the variable mixing intensity. Higher temperature, lower global irradiance and enhanced mixing generated lower algal biomass and primary production in the dynamic simulation model. This suggests that potential consequences of climate change may partly counteract each other. Y1 - 2007 UR - http://www.springerlink.com/content/p450177134590p61/ U6 - https://doi.org/10.1007/s00442-006-0547-4 ER - TY - JOUR A1 - Spijkerman, Elly A1 - Barua, Deepak A1 - Gerloff-Elias, Antje A1 - Gaedke, Ursula A1 - Heckathorn, S. A. T1 - Stress responses and metal tolerance of Chlamydomonas acidophila in metal-enriched lake water and artificial medium N2 - Chlamydomonas acidophila faces high heavy-metal concentrations in acidic mining lakes, where it is a dominant phytoplankton species. To investigate the importance of metals to C. acidophila in these lakes, we examined the response of growth, photosynthesis, cell structure, heat-shock protein (Hsp) accumulation, and metal adsorption after incubation in metal-rich lake water and artificial growth medium enriched with metals (Fe, Zn). Incubation in both metal-rich lake water and medium caused large decreases in photosystem II function (though no differences among lakes), but no decrease in growth rate (except for medium + Fe). Concentrations of small Hsps were higher in algae incubated in metal-rich lake- water than in metal-enriched medium, whereas Hsp60 and Hsp70A were either less or equally expressed. Cellular Zn and Fe contents were lower, and metals adsorbed to the cell surface were higher, in lake-water-incubated algae than in medium- grown cells. The results indicate that high Zn or Fe levels are likely not the main or only contributor to the low primary production in mining lakes, and multiple adaptations of C. acidophila (e.g., high Hsp levels, decreased metal accumulation) increase its tolerance to metals and permit survival under such adverse environmental conditions. Supposedly, the main stress factor present in the lake water is an interaction between low P and high Fe concentrations. Y1 - 2007 UR - http://www.springerlink.com/content/p7273234p8255263/ U6 - https://doi.org/10.1007/s00792-007-0067-0 ER - TY - JOUR A1 - Spijkerman, Elly A1 - Bissinger, Vera A1 - Gaedke, Ursula T1 - Low potassium and inorganic carbon concentrations influence a possible phosphorus limitation in Chlamydomonas acidophila N2 - Chlamydomonas acidophila, a dominant phytoplankton species in the very acidic Lake 111 (pH 2.7) situated in Germany, faces low concentrations of inorganic phosphorus (P-i), inorganic carbon (C-i) and potassium (K+) in its environment, which may lead to a complex colimitation by these nutrients. We performed laboratory and field investigations to test for P-i limitation and its dependence on C-i and K+ concentrations. The minimum cell quota for phosphorus (Q(0)) and phosphatase enzyme activity were similar to those for neutrophilic algae, despite the low pH and high concentrations of iron and aluminium, indicating no extra metabolic costs or inhibition of enzymes by the extreme environment. The threshold concentration of soluble reactive phosphorus for growth (SRPt), the algal C:P ratio and the alkaline phosphatase enzyme activity all suggested a moderate P-i limitation of C. acidophila in Lake 111. SRPt and Q(0) were higher at low CO2 and K+ concentrations in culture, showing a relationship between C-i and P-i acquisition. Furthermore, SRPt and Q(0) were higher under K+/P-i-colimiting conditions than under P-i-limiting conditions alone, suggesting that K+ concentrations influence P-i limitation in C. acidophila as well. Our results show that a limitation by one macronutrient requires consideration of the availability of the others as their uptake mechanisms depend on each other. Notwithstanding these interactions, C-i or K+ concentrations had no clear influence on the P-i limitation of C. acidophila in Lake 111. Y1 - 2007 UR - http://www.tandfonline.com/doi/full/10.1080/09670260701529596 U6 - https://doi.org/10.1080/09670260701529596 ER - TY - JOUR A1 - Bell, Elanor M. T1 - Seasonal changes in the concentration and metabolic activity of bacteria and viruses at an Antarctic coastal site N2 - Bacteria play a key role in the world's oceans, supporting nutrient remineralisation and mediating carbon transfer. Little is known about annual changes in bacterial concentration, production and metabolism during the extreme seasonal changes in biological productivity in Antarctic waters. We measured rates of bacterial production, concentrations of viruses and bacteria and environmental parameters between February 2004 and January 2005 at an Antarctic coastal site. Concentrations of total bacteria and viruses were obtained using 4', 6-diamidino-2- phenylindole (DAPI) and SYBR Green I (Molecular Probes), respectively. Populations of bacteria in different metabolic states were estimated using vital stains. Concentrations of bacteria with intact or compromised plasma membranes were estimated using BacLight (Molecular Probes) and active cells estimated using 6-carboxyfluorescein diacetate (6CFDA). Our study showed 6CFDA and BacLight gave rapid and ecologically valuable insights into bacterial physiology, production and growth in natural Antarctic communities that were poorly represented by changes in total cell concentrations. Concentrations of total, active and intact bacteria declined rapidly at the end of summer probably owing to viral infection and microheterotrophic grazing. The decline continued over winter, likely owing to substrate limitation, and concentrations only increased after the phytoplankton bloom in spring and summer. Bacterial abundance was positively correlated with particulate organic carbon (POC) and nitrogen (PON), but not dissolved organic carbon (DOC), reflecting the refractory nature of the DOC pool. Only active and intact bacteria were significantly correlated with concentrations of chl a and rates of bacterial production. Furthermore, the obtained rates of [H-3]thymidine uptake suggest that bacterial growth rates can be sustained by the populations identified as intact or by active cells alone. Y1 - 2007 UR - http://www.int-res.com/abstracts/ame/v47/n1/ ER - TY - JOUR A1 - Hoffmann, Armin S. A1 - Kane, Avinash S. A1 - Nettels, Daniel A1 - Hertzog, David E. A1 - Baumgärtel, Peter A1 - Lengefeld, Jan A1 - Reichardt, Gerd A1 - Horsley, David A. A1 - Seckler, Robert A1 - Bakajin, Olgica A1 - Schuler, Benjamin T1 - Mapping protein collapse with single molecule fluorescence and kinetic synchrotron radiation circular dichroism spectroscopy Y1 - 2007 UR - http://www.mendeley.com/research/mapping-protein-collapse-with-singlemolecule-fluorescence-and-kinetic- synchrotron-radiation-circular-dichroism-spectroscopy/# SN - 0027-8424 ER - TY - JOUR A1 - Gast, Klaus A1 - Modler, Andreas Johannes T1 - Dynamic and static light scattering of proteins Y1 - 2007 SN - 978-1-600-21704-3 ER - TY - JOUR A1 - Mishra, Rajesh A1 - Bhat, Rajiv A1 - Seckler, Robert T1 - Chemical chaperone mediated protein folding : stabilization of P22 tailspike folding intermediates by glycerol Y1 - 2007 SN - 1431-6730 ER - TY - JOUR A1 - Weithoff, Guntram A1 - Wacker, Alexander T1 - The mode of nutrition of mixotrophic flagellates determines the food quality for their consumers Y1 - 2007 UR - http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2007.01333.x/full U6 - https://doi.org/10.1111/j.1365-2435.2007.01333.x ER -