Effects of food on bacterial community composition associated with the copepod Acartia tonsa Dana

The estuarine copepod Acartia tonsa naturally carried diverse strains of bacteria on its body. The bacterial community composition (BCC) remained very conservative even when the copepod was fed different axenic algal species, indicating that the food per se did not much affect BCC associated with the copepod. In xenic algal treatments, however, copepod-associated BCC differed with each alga fed, even though the same bacterial source was used to inoculate the algae. In addition, starved copepods taken at the same location but at different times significantly differed in their BCC. Algal species composition and copepod life history therefore serve to regulate BCC associated with copepods, and spatial and temporal variations in algal species composition and copepod origin would alter bacteria-copepod interactions

The response of temperate aquatic ecosystems to global warming: novel insights from a multidisciplinary project

This article serves as an introduction to this special issue of Marine Biology, but also as a review of the key findings of the AQUASHIFT research program which is the source of the articles published in this issue. AQUASHIFT is an interdisciplinary research program targeted to analyze the response of temperate zone aquatic ecosystems (both marine and freshwater) to global warming. The main conclusions of AQUASHIFT relate to (a) shifts in geographic distribution, (b) shifts in seasonality, (c) temporal mismatch in food chains, (d) biomass responses to warming, (e) responses of body size, (f) harmful bloom intensity, (f), changes of biodiversity, and (g) the dependence of shifts to temperature changes during critical seasonal windows

Microbial activities accompanying decomposition of cladoceran and copepod carcasses under different environmental conditions

Cladoceran and copepod carcasses in both marine and freshwater environments represent concentrated reservoirs of organic substrates for water column bacteria. We studied the microbial abundance, activities, and diversity associated with decomposing carcasses of different zooplankton species over short and long time scales, and in oligotrophic vs. eutrophic environments. Fresh carcasses of Daphnia cucullata, Diaphanosoma brachyurum, and Eudiaptomus gracilis were rapidly colonized by bacteria, which reached peak abundances within 1.5 d at 20 degrees C and then decreased. Cell-specific exoenzymatic activity on protein and lipid analogs and production rate of bacteria associated with the carcasses were all higher than in the ambient water. ANOSIM analyses of DGGE banding patterns revealed that bacterial communities associated with both cladoceran and copepod carcasses rapidly diverged from the initial bacterial community in the ambient water. The high similarity of bacteria on both types of carcasses indicates that the carcasses were decomposed by similar bacterial groups. Estimated carcass decomposition rate was lower at 6 degrees C, with an estimated Q(10) of 2.4. Carcasses suspended in the eutrophic Lake Dagow had a higher average carbon loss rate than those suspended in the oligotrophic Lake Stechlin. Cladoceran carcasses were initially colonized by bacteria faster than copepod carcasses in both laboratory and field experiments, suggesting that cladoceran carcasses were more prone to exploitation by bacteria, yet copepod carcasses lost carbon at higher rates. Overall, our results suggest that pelagic zooplankton production can be directly converted to water column bacterial production via carcass decomposition, especially during the mid-summer zooplankton decline commonly observed in lakes

Adopting a New Practice: Open Source Experiences in the Classroom

This Research Full Paper describes a case study of educators changing practice as a result of interactions with an open source software community. It examines an NSF-funded initiative designed to expose educators to humanitarian free and open source software (HFOSS) communities and, in turn, to support them in involving their students in these communities as part of their classroom experience. To date, more than 150 faculty from over 120 different institutions have participated in the initiative’s faculty development workshops. In this work, we conducted in-depth interviews with 24 workshop participants. The interviews explored how faculty had adopted HFOSS in the classroom, the hurdles and successes they encountered, and how their teaching had changed, among other questions. Some of the themes we identify in our data – obstacles to adoption, such as a lack of time, and the importance of the institutional context – confirm prior findings in the literature on pedagogical change. However, this work also identifies several additional nuances that have not previously been reported and emphasizes common aspects among educators who successfully adopted a practice

Bacteria dispersal by hitchhiking on zooplankton

Microorganisms and zooplankton are both important components of aquatic food webs. Although both inhabit the same environment, they are often regarded as separate functional units that are indirectly connected through nutrient cycling and trophic cascade. However, research on pathogenic and nonpathogenic bacteria has shown that direct association with zooplankton has significant influences on the bacteria's physiology and ecology. We used stratified migration columns to study vertical dispersal of hitchhiking bacteria through migrating zooplankton across a density gradient that was otherwise impenetrable for bacteria in both upward and downward directions (conveyor-belt hypothesis). The strength of our experiments is to permit quantitative estimation of transport and release of associated bacteria: vertical migration of Daphnia magna yielded an average dispersal rate of 1.3 × 105·cells·Daphnia−1·migration cycle−1 for the lake bacterium Brevundimonas sp. Bidirectional vertical dispersal by migrating D. magna was also shown for two other bacterial species, albeit at lower rates. The prediction that diurnally migrating zooplankton acquire different attached bacterial communities from hypolimnion and epilimnion between day and night was subsequently confirmed in our field study. In mesotrophic Lake Nehmitz, D. hyalina showed pronounced diel vertical migration along with significant diurnal changes in attached bacterial community composition. These results confirm that hitchhiking on migrating animals can be an important mechanism for rapidly relocating microorganisms, including pathogens, allowing them to access otherwise inaccessible resources

Microbial methane production in oxygenated water column of an oligotrophic lake

The prevailing paradigm in aquatic science is that microbial methanogenesis happens primarily in anoxic environments. Here, we used multiple complementary approaches to show that microbial methane production could and did occur in the well-oxygenated water column of an oligotrophic lake (Lake Stechlin, Germany). Oversaturation of methane was repeatedly recorded in the well-oxygenated upper 10 m of the water column, and the methane maxima coincided with oxygen oversaturation at 6 m. Laboratory incubations of unamended epilimnetic lake water and inoculations of photoautotrophs with a lake-enrichment culture both led to methane production even in the presence of oxygen, and the production was not affected by the addition of inorganic phosphate or methylated compounds. Methane production was also detected by in-lake incubations of lake water, and the highest production rate was 1.8–2.4 nM⋅h−1 at 6 m, which could explain 33–44% of the observed ambient methane accumulation in the same month. Temporal and spatial uncoupling between methanogenesis and methanotrophy was supported by field and laboratory measurements, which also helped explain the oversaturation of methane in the upper water column. Potentially methanogenic Archaea were detected in situ in the oxygenated, methane-rich epilimnion, and their attachment to photoautotrophs might allow for anaerobic growth and direct transfer of substrates for methane production. Specific PCR on mRNA of the methyl coenzyme M reductase A gene revealed active methanogenesis. Microbial methane production in oxygenated water represents a hitherto overlooked source of methane and can be important for carbon cycling in the aquatic environments and water to air methane flux

Untersuchungen zum Alkalitaetsverhalten des Betons und zum Korrosionszustand des Stahls Anlage 3 zur Forschungsarbeit 'Bauzustandsermittlung und Schadensursachenforschung an einem zum Abriss vorgesehenen Plattenbau'

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