Assessing carbon dynamics in natural and perturbed boreal aquatic systems

Most natural freshwater lakes are net greenhouse gases (GHG) emitters. Compared to 25 natural systems, human perturbations such as watershed wood harvesting and long term reservoir 26 impoundment lead to profound alterations of biogeochemical processes involved in the aquatic 27 cycle of carbon (C). We exploited these anthropogenic alterations to describe the C dynamics in 28 five lakes and two reservoirs from the boreal forest through the analysis of dissolved carbon 29 dioxide (CO2), methane (CH4), oxygen (O2), and organic carbon (DOC), as well as total nitrogen 30 (TN) and phosphorus (TP). Dissolved and particulate organic matter, forest soil/litter and 31 leachates, as well as dissolved inorganic carbon (DIC) were analyzed for elemental and stable 32 isotopic compositions (atomic C:N ratios, δ13Corg, δ13Cinorg and δ15Ntot). We found links between 33 the export of terrestrial OM to these systems and the dissolved CO2 and O2 concentrations in the 34 water column, as well as CO2 fluxes to the atmosphere. All systems were GHG emitters, with 35 greater emissions measured for systems with larger inputs of terrestrial OM. The differences in 36 CO2 concentrations and fluxes appear controlled by bacterial activity in the water column and the 37 sediment. Although we clearly observed differences in the aquatic C cycle between natural and 38 perturbed systems, more work on a larger number of water bodies, and encompassing all four 39 seasons should be undertaken to better understand the controls, rates, as well as spatial and 40 temporal variability of GHG emissions, and to make quantitatively meaningful comparisons of 41 GHG emissions (and other key variables) from natural and perturbed systems

Design and characterization of a direct ELISA for the detection and quantification of leucomalachite green

Malachite green (MG), a member of the N-methylated triphenylmethane class of dyes, has long been used to control fungal and protozoan infections in fish. MG is easily absorbed by fish during waterborne exposure and is rapidly metabolized into leucomalachite green (LMG), which is known for its long residence time in edible fish tissue. This paper describes the development of an enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of LMG in fish tissue. This development includes a simple and versatile method for the conversion of LMG to monodesmethyl-LMG, which is then conjugated to bovine serum albumin (BSA) to produce an immunogenic material. Rabbit polyclonal antibodies are generated against this immunogen, purified and used to develop a direct competitive enzyme-linked immunosorbent assay (ELISA) for the screening and quantification of LMG in fish tissue. The assay performed well, with a limit of detection (LOD) and limit of quantification (LOQ) of 0.1 and 0.3 ng g−1 of fish tissue, respectively. The average extraction efficiency from a matrix of tilapia fillets was approximately 73% and the day-to-day reproducibility for these extractions in the assay was between 5 and 10%

Acclimation of Saccharomyces cerevisiae to Low Temperature: A Chemostat-based Transcriptome Analysis

Effects of suboptimal temperatures on transcriptional regulation in yeast have been extensively studied in batch cultures. To eliminate indirect effects of specific growth rates that are inherent to batch-cultivation studies, genome-wide transcriptional responses to low temperatures were analyzed in steady-state chemostats, grown at a fixed specific growth rate (0.03 h−1). Although in vivo metabolic fluxes were essentially the same in cultures grown at 12 and at 30°C, concentrations of the growth-limiting nutrients (glucose or ammonia) were higher at 12°C. This difference was reflected by transcript levels of genes that encode transporters for the growth-limiting nutrients. Several transcriptional responses to low temperature occurred under both nutrient-limitation regimes. Increased transcription of ribosome-biogenesis genes emphasized the importance of adapting protein-synthesis capacity to low temperature. In contrast to observations in cold-shock and batch-culture studies, transcript levels of environmental stress response genes were reduced at 12°C. Transcription of trehalose-biosynthesis genes and intracellular trehalose levels indicated that, in contrast to its role in cold-shock adaptation, trehalose is not involved in steady-state low-temperature adaptation. Comparison of the chemostat-based transcriptome data with literature data revealed large differences between transcriptional reprogramming during long-term low-temperature acclimation and the transcriptional responses to a rapid transition to low temperature