bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential for Development of an Escherichia coli—Based Biosensor for Assessing Bioavailable Methionine: A Review
Authors: Chalova Vesela I. , Froelich Clifford A. , Ricke Steven C.
Published: April 2010

Methionine is an essential amino acid for animals and is typically considered one of the first limiting amino acids in animal feed formulations. Methionine deficiency or excess in animal diets can lead to sub-optimal animal performance and increased environmental pollution, which necessitates its accurate quantification and proper dosage in animal rations. Animal bioassays are the current industry standard to quantify methionine bioavailability. However, animal-based assays are not only time consuming, but expensive and are becoming more scrutinized by governmental regulations. In addition, a variety of artifacts can hinder the variability and time efficacy of these assays. Microbiological assays, which are based on a microbial response to external supplementation of a particular nutrient such as methionine, appear to be attractive potential alternatives to the already established standards. They are rapid and inexpensive in vitro assays which are characterized with relatively accurate and consistent estimation of digestible methionine in feeds and feed ingredients. The current review discusses the potential to develop Escherichia coli-based microbial biosensors for methionine bioavailability quantification. Methionine biosynthesis and regulation pathways are overviewed in relation to genetic manipulation required for the generation of a respective methionine auxotroph that could be practical for a routine bioassay. A prospective utilization of Escherichia coli methionine biosensor would allow for inexpensive and rapid methionine quantification and ultimately enable timely assessment of nutritional profiles of feedstuffs.
Symmetry and Asymmetry Level Measures
Authors: Garrido Angel
Published: April 2010

Usually, Symmetry and Asymmetry are considered as two opposite sides of a coin: an object is either totally symmetric, or totally asymmetric, relative to pattern objects. Intermediate situations of partial symmetry or partial asymmetry are not considered. But this dichotomy on the classification lacks of a necessary and realistic gradation. For this reason, it is convenient to introduce "shade regions", modulating the degree of Symmetry (a fuzzy concept). Here, we will analyze the Asymmetry problem by successive attempts of description and by the introduction of the Asymmetry Level Function, as a new Normal Fuzzy Measure. Our results (both Theorems and Corollaries) suppose to be some new and original contributions to such very active and interesting field of research. Previously, we proceed to the analysis of the state of art.
The Effects of Cholera Toxin on Cellular Energy Metabolism
Authors: Snider Rachel M. , McKenzie Jennifer R. , Kraft Lewis , Kozlov Eugene , Wikswo John P. , Cliffel David E.
Published: April 2010

Multianalyte microphysiometry, a real-time instrument for simultaneous measurement of metabolic analytes in a microfluidic environment, was used to explore the effects of cholera toxin (CTx). Upon exposure of CTx to PC-12 cells, anaerobic respiration was triggered, measured as increases in acid and lactate production and a decrease in the oxygen uptake. We believe the responses observed are due to a CTx-induced activation of adenylate cyclase, increasing cAMP production and resulting in a switch to anaerobic respiration. Inhibitors (H-89, brefeldin A) and stimulators (forskolin) of cAMP were employed to modulate the CTx-induced cAMP responses. The results of this study show the utility of multianalyte microphysiometry to quantitatively determine the dynamic metabolic effects of toxins and affected pathways.
Anatomical relations among endophytic holoparasitic angiosperms, autotrophic host plants and mycorrhizal fungi: A novel tripartite interaction
Authors: de Vega Clara , Arista Montserrat , Ortiz Pedro L. , Talavera Salvador
Published: April 2010

Mycorrhizae are widespread mutualistic symbioses crucial for the functioning of terrestrial ecosystems. Not all plants associate with mycorrhizae; most parasitic plants have been suggested to be nonmycorrhizal because they have developed alternative strategies to obtain nutrients. In endophytic parasitic plants, whose vegetative bodies grow completely inside their mycorrhizal host roots, the opportunity for establishing a tripartite association seems evident, but information on these systems is lacking. In studying natural associations among the endophytic holoparasite Cytinus hypocistis, their Cistaceae host species, and associated mycorrhizal fungi, we found that mycorrhizae were associated with the hosts and the parasites, reaching high frequencies of colonization. In parasitic and host root tissues, mycorrhizal fungi spread in the parenchymatic cells by intracellular growth and formed hyphal coils and vesicles, while the cambium and the vascular tissues were never colonized. This report is the first on a tripartite association of an endophytic parasitic plant, its host, and mycorrhizae in natural conditions, representing a novel trophic interaction not previously reported within the angiosperms. Additional studies on the interactions occurring among these three players are needed because they may be crucial to our understanding of how this mutualistic‐antagonistic system is functioning and evolving.
A thermally-induced, tandem [3,3]-sigmatropic rearrangement/[2 + 2] cycloaddition approach to carbocyclic spirooxindoles
Authors: Brummond Kay M , Osbourn Joshua M
Published: April 2010

The synthesis of C3-carbocyclic spirooxindoles was realized by way of an intramolecular [2 + 2] cycloaddition reaction between a vinylidene indolin-2-one and an alkyne. The cycloaddition reaction occurs selectively with the distal double bond of the allene, is tolerant of a phenyl and trimethylsilyl group on the terminus of the alkyne, and can be used to access bicyclo[4.2.0]octadienes and bicyclo[5.2.0]nonadienes. The allene precursors are not observed, but are likely intermediates of an infrequently encountered thermal [3,3]-sigmatropic rearrangement of a propargylic acetate.
TRIF Signaling Stimulates Translation of TNF-α mRNA via Prolonged Activation of MK2
Authors: Gais Petra , Tiedje Christopher , Altmayr Felicitas , Gaestel Matthias , Weighardt Heike , Holzmann Bernhard
Published: April 2010

The adapter protein TRIF mediates signal transduction through TLR3 and TLR4, inducing production of type I IFNs and inflammatory cytokines. The present study investigates the mechanisms by which TRIF signaling controls TNF-α biosynthesis. We provide evidence that, in LPS-stimulated murine dendritic cells, TRIF stimulates TNF-α biosynthesis selectively at the posttranscriptional level by promoting mRNA translation. In the absence of functional TRIF, the production of TNF-α protein was severely impaired, whereas TNF-α mRNA levels and stability, as well as transcriptional activity of the Tnfa gene, were not affected. Similarly, TRIF was required for production of LPS-induced TNF-α protein, but not of mRNA, in bone marrow-derived macrophages. In peritoneal macrophages, however, TRIF was also required for normal induction of TNF-α mRNA, suggesting cell type-related functions of TRIF. The influence of TRIF on dendritic cell TNF-α production was independent of type I IFNs. TRIF was required for prolonged activation of MAPKs in LPS-stimulated dendritic cells but was dispensable for the activation of NF-κB. Inhibition of late p38 activity attenuated LPS-stimulated elevation of TNF-α protein but not mRNA levels. The p38 effector kinase MK2 was directly activated through the TRIF pathway of TLR4. Importantly, stimulation of Mk2−/− cells through TLR3 or TLR4 severely impaired TNF-α protein production but did not affect TNF-α mRNA induction. Together, these results indicate that the TRIF signaling pathway promotes TNF-α mRNA translation through activation of the protein kinase MK2.
Induction of Distinct Neurologic Disease Manifestations during Relapsing Fever Requires T Lymphocytes
Authors: Liu Hongqi , Fitzgerald Denise , Gran Bruno , Leong John M. , Alugupalli Kishore R.
Published: April 2010

Relapsing fever borreliosis is a multisystemic infection characterized primarily by bacteremia but can extend to the CNS. The incidence of CNS disease manifestations in humans depends on the infecting relapsing fever Borrelia species. In the murine model of Borrelia hermsii infection we found high incidence of distinct signs of CNS disease that ranged from a flaccid tail to complete paralysis of hind limbs. Infiltration of large number of T cells into the spinal cord of B. hermsii-infected mice and the upregulation of MHC class II and CD80 on infiltrating macrophages and on microglial cells suggested a role for T cell and Ag-presenting cell interactions in this pathogenesis. Indeed, B. hermsii infection did not induce CNS disease manifestations in T cell-deficient mice (TCR-β × δ−/−), although it resulted in bacteremia comparable to wild-type (Wt) level. Moreover, the infiltration of immune cells into the spinal cord of TCR-β × δ−/− mice was reduced and the resident microglial cells were not activated. Histopathological analysis of lumbar sections of the spinal cord confirmed severe inflammation in Wt but not in TCR-β × δ−/− mice. Induction of CNS disease was dependent on the B. hermsii strain as well as on the ability of the host to control bacteremia. Mice that are impaired in controlling B. hermsii, such as CD14−/− mice, exhibited more severe CNS disease than Wt mice. This study demonstrates that distinct neurologic disease manifestations develop during relapsing fever and that T cells play a critical role in the induction of neuropathogenesis.
miR-146a Is Differentially Expressed by Myeloid Dendritic Cell Subsets and Desensitizes Cells to TLR2-Dependent Activation
Authors: Jurkin Jennifer , Schichl Yvonne M. , Koeffel Rene , Bauer Thomas , Richter Susanne , Konradi Sabine , Gesslbauer Bernhard , Strobl Herbert
Published: April 2010

Langerhans cells (LCs) in epithelia and interstitial dendritic cells (intDCs) in adjacent connective tissues represent two closely related myeloid-derived DC subsets that exert specialized functions in the immune system and are of clinical relevance for cell therapy. Both subsets arise from monocyte-committed intermediates in response to tissue-associated microenvironmental signals; however, molecular mechanisms underlying myeloid DC subset specification and function remain poorly defined. Using microarray profiling, we identified microRNA (miRNA) miR-146a to be constitutively expressed at higher levels in human LCs compared with intDCs. Moreover, miR-146a levels were low in monocytes and nondetectable in neutrophil granulocytes. Interestingly, constitutive high miR-146a expression in LCs is induced by the transcription factor PU.1 in response to TGF-β1, a key microenvironmental signal for epidermal LC differentiation. We identified miR-146a as a regulator of monocyte and DC activation but not myeloid/DC subset differentiation. Ectopic miR-146a in monocytes and intDCs interfered with TLR2 downstream signaling and cytokine production, without affecting phenotypic DC maturation. Inversely, silencing of miR-146a in LCs enhanced TLR2-dependent NF-κB signaling. We therefore conclude that high constitutive miR-146a levels are induced by microenvironmental signals in the epidermis and might render LCs less susceptible to inappropriate activation by commensal bacterial TLR2 triggers at body surfaces.
Mesenchymal Stem Cells Protect Breast Cancer Cells through Regulatory T Cells: Role of Mesenchymal Stem Cell-Derived TGF-β
Authors: Patel Shyam A. , Meyer Justin R. , Greco Steven J. , Corcoran Kelly E. , Bryan Margarette , Rameshwar Pranela
Published: April 2010

Mesenchymal stem cells (MSCs) have been shown to support breast cancer growth. Because MSCs also increase the frequency of regulatory T cells (Tregs), this study tested the hypothesis that human MSCs, via Tregs, protect breast cancer cells (BCCs) from immune clearance MSCs suppressed the proliferation of PBMCs when the latter were exposed to gamma-irradiated BCCs. Similarly, MSCs showed significant inhibition of PBMC migration toward BCCs and a corresponding decrease in CXCL12. MSCs also inhibited NK cell and CTL functions, which correlated with reduced numbers of CD8+ and CD56+ cells compared with parallel cultures without MSCs. The reduced NK and CTL activities correlated with a decrease in intracellular and secreted granzyme B. To explain these immunosuppressive findings, we compared Treg levels after coculture with MSCs and found an ∼2-fold increase in Tregs, with associated decreases in antitumor Th1 cytokines and increases in Th2 cytokines. MSC-derived TGF-β1 was largely responsible for the increase in Tregs based on knockdown studies. In the presence of Treg depletion, PBMC proliferation and effector functions were partially restored. Together, these studies show an MSC-mediated increase in Tregs in cocultures of PBMCs and BCCs. The results could be explained, in part, by the increase in Th2-type cytokines and MSC-generated TGF-β1. These findings demonstrate immune protection by MSCs to BCCs. The reduction in immune cell proliferation and recruitment mediated by MSCs has implications for treatment of breast cancer with chemotherapy.
B7-H1 Expression on Old CD8+ T Cells Negatively Regulates the Activation of Immune Responses in Aged Animals
Authors: Mirza Noweeda , Duque Maria Adelaida , Dominguez Ana Lucia , Schrum Adam G. , Dong Haidong , Lustgarten Joseph
Published: April 2010

T cell responses are compromised in the elderly. The B7-CD28 family receptors are critical in the regulation of immune responses. We evaluated whether the B7-family and CD28-family receptors were differentially expressed in dendritic cells, macrophages, and CD4+ and CD8+ T cells from young and old mice, which could contribute to the immune dysfunction in the old. Although most of the receptors were equally expressed in all cells, >85% of the old naive CD8+ T cells expressed B7-H1 compared with 25% in the young. Considering that B7-H1 negatively regulates immune responses, we hypothesized that expression of B7-H1 would downregulate the function of old CD8+ T cells. Old CD8+ T cells showed reduced ability to proliferate, but blockade of B7-H1 restored the proliferative capacity of old CD8+ T cells to a level similar to young CD8+ T cells. In vivo blockade of B7-H1 restored antitumor responses against the B7-H1− BM-185–enhanced GFP tumor, such that old animals responded with the same efficiency as young mice. Our data also indicate that old CD8+ T cells express lower levels of TCR compared with young CD8+ T cells. However, following antigenic stimulation in the presence of B7-H1 blockade, the levels of TCR expression were restored in old CD8+ T cells, which correlated with stronger T cell activation. These studies demonstrated that expression of B7-H1 in old CD8+ T cells impairs the proper activation of these cells and that blockade of B7-H1 could be critical to optimally stimulate a CD8 T cell response in the old.
The importance of boundary‐layer flows in supplying phytoplankton to the benthic suspension feeder, Mytilus edulis L.
Authors: Fréchette Marcel , Butman Cheryl Ann , Geyer W. Rockwell
Published: April 2010

Measurements of vertical gradients in phytoplankton fluorescence over an intertidal mussel bed in the St. Lawrence River estuary (Québec) indicate a significant reduction in phytoplankton concentration close to the bed. Furthermore, measurements of near#x2010;bed fluorescence as a function of current speed, and of mussel consumption rate as a function of in situ fluorescence, suggest that consumption rate varies with flow speed. A steady, two#x2010;dimensional, finite#x2010;difference model was constructed to represent the balance between horizontal advection and vertical diffusion of phytoplankton over a mussel bed, in order to simulate the observed influence of mussels on the phytoplankton distribution. The vertical distribution of phytoplankton generated by the model shows a marked reduction close to the bed, consistent with the field measurements, and the model also confirms the dependence of consumption rate on flow speed. Enhanced vertical diffusive transport at higher current speeds results in a higher rate of replenishment of phytoplankton to food#x2010;impoverished near#x2010;bottom waters. Model runs with different values of the bottom roughness parameter indicate that roughness due to the mussels themselves may significantly increase the food supply to the bed, due to enhanced turbulent transport. In addition, since there is a strong vertical gradient in food concentration above the seabed, the time#x2010;averaged food concentration obtained by the mussels is a strong function of the height from which they ingest.
Production of dimethylsulfonium propionate and dimethylsulfide by phytoplankton in estuarine and coastal waters
Authors: Iverson R. L. , Nearhoof F. L. , Andreae M. O.
Published: April 2010

We determined the concentrations of dimethylsulfide (DMS) and its metabolic precursor, dimethylsulfonium propionate (DMSP), in water and particulate samples obtained along transects through Delaware Bay, Chesapeake Bay (including the Potomac River), and Ochlockonee Bay (Florida). The Delaware and Chesapeake Bay transects extended into the open ocean. In most cases, we observed positive correlations between the concentrations of the biogenic sulfur species and salinity, particularly when the concentrations of the sulfur compounds were normalized to chlorophyll a as a measure of phytoplankton biomass. The normalized concentrations of DMS, dissolved DMSP, and particulate (intracellular) DMSP increased nonlinearly with salinity from estuarine through shelf to oceanic environments. Within each environment, dissolved DMS and dissolved and particulate DMSP correlated more strongly with salinity than with phytoplankton species composition. On the other hand, the sharp increases in Chl a#x2010;normalized biogenic sulfur concentrations from the estuarine to the coastal and shelf environments were most strongly correlated with differences in the species composition of the phytoplankton community between environments and appear to reflect differences in DMSP production between oceanic, coccolithophore#x2010;dominated communities and estuarine, diatom#x2010;dominated communities.
Modeling the effects of temperature, light, and nutrients on primary productivity: An empirical and a mechanistic approach compared
Authors: Keller Aimee A.
Published: April 2010

The prospect of reliably predicting production from environmental variables in heterogeneous estuarine environments offers clear logistic advantages over measurement with the 14C technique, particularly if detailed coverage (in space and time) is desired. To that end, two different techniques for predicting phytoplankton production were tested and compared using data from Narragansett Bay, R.I., and experimental estuarine ecosystems. Primary productivity was first estimated via an empirical technique (principal component regression), which incorporated temperature, light, and nutrients as independent variables. This approach was compared with a traditional mechanistic formulation which included the same environmental variables as the major limiting factors. Both models provided good fits to the data (explaining 77–82% of the total variance). The predictive ability of the mechanistic model was significantly greater (P < 0.05) than the principal component regression when tested on two independent data sets. Predictive ability between the two models was statistically compared by F#x2010;tests on the residual variability from each method.
Discrimination of phytoplankton via light‐scattering properties
Authors: Wyatt Philip J. , Jackson Christian
Published: April 2010

Measurements of multiangle light scattering were made on individual phytoplankter cells in vitro by means of a commercial light#x2010;scattering photometer and in situ with a new instrument capable of measurements in an unconfined environment. Both instruments contain collimated detectors that measure light scattered from a small, defined#x2010;volume element of a detector#x2010;circumscribed, plane#x2010;polarized laser beam. As a single phytoplankter enters this volume, a scattering signal detected at a selected angle triggers repeated electronic scans of the particle as it moves through the volume. Data collected at up to 16 distinct angles are recorded 100 times during a period of a few hundred milliseconds. A subsequent analysis of data from 1,265 individual phytoplankters covering 12 distinct species confirms (for this group) the hypothesis that different species of phytoplankton produce distinctive scattering signals.
Analyzing zooplankton size distributions using high‐frequency sound
Authors: Greene Charles H. , Wiebe Peter H. , Burczynski Janusz
Published: April 2010

A high#x2010;frequency, dual#x2010;beam acoustical technique for directly estimating the size distributions within zooplankton assemblages has been developed. In combination with data from echo integration, acoustical size distributions can be used to apportion zooplankton numerical density and biomass concentration into different size classes. Two major conclusions can be drawn from calibration experiments and preliminary field studies using the technique: the backscattering intensities from individual zooplankters increase proportionally with the cubes of their lengths; and the combination of dual#x2010;beam and echo#x2010;integration techniques has the potential to produce rapid, high#x2010;resolution, size#x2010;specific data on zooplankton distributions in the water column.
A steady state description ofgrowth and light absorption in the marine planktonic diatom Skeletonema costatum
Authors: Sakshaug Egil , Andresen Kjersti , Kiefer Dale A.
Published: April 2010

Studies of the marine diatom Skeletonema costatum indicate that for a given irradiance and day length, increases in the rate of supply of a limiting nutrient cause linearly proportional increases in the growth rate and the Chl : C ratio. For a given irradiance, increases in day length cause decreases in the Chl : C ratio, and the growth rate is linearly proportional to the product of day length and the Chl : C ratio. For a given day length, increases in irradiance cause decreases in the Chl : C ratio and quantum yield, and the growth rate and irradiance are curvilinearly related.

These observations are incorporated into a formulation of steady state growth, which includes day length, irradiance, and the Chl : C ratio, and two coefficients, which are the product of the maximal quantum yield and the specific absorption coefficient and the product of the average absorption cross section of the photosynthetic unit and the minimal rate of turnover of the unit. The photosynthetic quantum yield is represented by a Poisson distribution and is a function of irradiance alone.
Differences in silica content between marine and freshwater diatoms
Authors: Conley Daniel J. , Kilham Susan S. , Theriot Edward
Published: April 2010

Marine diatoms are shown to have on average one order of magnitude less silica per unit of biovolume than freshwater species. Silica content (pmol cell−1) increases linearly with biovolume (µm3) in both marine (1og10[silica content] = 0.91 log10[biovolume] — 3.16; r = 0.92; P < 0.0001; N = 44) and freshwater diatoms (log10[silica content] = 1.03 1og10[biovolume] — 2.45; r = 0.91; P < 0.0001; N = 62). Therefore, a first#x2010;order estimate of the amount of silica utilized by diatom production can be made from diatom biovolumes. Si: C molar ratios for marine diatoms and for freshwater diatoms also are different and demonstrate that appropriate molar ratios must be used for marine and freshwaters in estimating biogenic silica production from primary production. Among possible reasons for the disparity are differences in sinking strategy, the adaptation of marine diatom species to a low dissolved silica environment, and differences in salinity between the two environments.
The role of endosymbiotic bacteria in the nutrition of Solemya velum: Evidence from a stable isotope analysis of endosymbionts and host
Authors: Conway Noellette , Capuzzo Judith McDowell , Fry Brian
Published: April 2010

C, N, and S stable isotope compositions were investigated in tissues of the protobranch bivalve Solemya velum. This species is known to harbor endosymbiotic chemoautotrophic bacteria. C and N isotope values were also examined in an enriched bacterial fraction, separated from intact gills by differential centrifugation.

The bacterial fraction and host tissues had similar δ13C values, suggesting that endosymbiotic bacteria provide as much as 98% of the carbon requirements of S. velum. The δ15N values of both S. velum and the endosymbionts were comparable and considerably lower than those of bivalve controls that do not harbor endosymbionts. Uptake of pore‐water ammonium by the endosymbionts and subsequent translocation of nitrogenous compounds to the host may account for the low δ15N of S. velum. In this context, the symbionts may provide 100% of the host nitrogen. The δ34S values of S. velum suggest the use of biogenically produced H2S as a source of S. The stable isotope ratios of sulfur and nitrogen are among the lowest reported for animal tissues. This study attempts to estimate the nutritional significance of bacterial endosymbionts by analyzing the stable isotope ratios of both bacteria and host tissue.
Protein measurement and energetic considerations: Comparisons of biochemical and stoichiometric methods using bovine serum albumin and protein isolated from sea anemones
Authors: Zamer William E. , Shick J. Malcolm , Tapley David W.
Published: April 2010

Use of bovine serum albumin (BSA) as standard resulted in consistent underestimates of protein in tissues of cnidarians when either microbiuret or Bradford (Coomassie blue) analytical procedures were used. Slopes of the linear plots of absorbance vs. quantity of protein isolated from the sea anemones Anthopleura elegantissima and Aiptasia sp. were lower than the ones for BSA. Crude protein from sea anemones is not soluble in water, but dissolves in 10% NaOH—a solvent that interferes with the Lowry method, probably the most commonly used method of protein quantification among researchers studying cnidarians. Therefore choice of an appropriate solvent complicates the use of the Lowry procedure, since total protein may be underestimated if deionized water or a weaker base is used as solvent in either extraction or quantification. Values for the biochemical composition of tissues of A. elegantissima as determined by routine biochemical methods and CHN stoichiometric analysis are in agreement, but only after correction for the presence of substantial amounts of glycoprotein in total anemone protein. Glycoprotein components of total tissue protein may lead to similar errors in spectrophotometric quantification of protein in other marine invertebrates.
Complexation of zinc by natural organic ligands in the central North Pacific
Authors: Bruland Kenneth W.
Published: April 2010

The complexation of zinc by natural organic ligands in the upper 600 m of the central North Pacific was determined with differential pulse anodic stripping voltammetry at a thin mercury film, rotating glassy‐carbon disk electrode. Of the dissolved zinc in surface waters >98% was bound in strong complexes (log K′cond, Zn2+ = 11.0) by relatively zinc‐specific organic ligands existing at low concentrations (1.2 nM). Although the vertical distribution of this ligand class is relatively uniform, total dissolved zinc varies from concentrations close to 0.1 nM in surface waters of the central North Pacific to 3 nM at 500 m. Complexation of dissolved zinc by this class of organic ligands causes the concentration of inorganic zinc to vary from 2 pM in surface waters to 2 nM at 500 m, a 1,000‐fold variation. The free zinc ion activity, expressed as pZn, is calculated to be of the order of 12.7 in the surface waters of the central North Pacific. This low free zinc ion activity may influence distributions of oceanic and neritic phytoplankton species.
Bacterial activity and protozoan grazing potential in a stratified lake
Authors: Bloem Jaap , Bär‐Gilissen Marie‐José B.
Published: April 2010

During summer stratification in Lake Vechten, heterotrophic nanoflagellates (HNAN) showed peak densities at very low oxygen concentrations in the lower metalimnion at a depth of 6–7 m. In this stratum, high HNAN numbers (>30 × 106 HNAN liter−1) coincided with high bacterial activity. Assuming a conversion factor of 2 × 1018 bacteria mol−1 thymidine, we estimated a maximal bacterial production of about 4 × 109 bacteria liter−1 d−1 from thymidine incorporation. In the upper metalimnion (5–6‐m depth) we found a low bacterial activity (estimated production 1 × 108 bacteria liter−1 d−1) and low HNAN numbers (3 × 106 HNAN liter−1). HNAN seem to be a link in the food web between bacteria and cyanobacteria on the one hand and ciliates on the other. Grazing experiments with selectively filtered lake water indicated ingestion rates of about 7 bacteria HNAN−1 h−1. We calculated that the metalimnetic HNAN are able to consume the entire bacterial production even at high bacterial growth rates.
Effects of Si : P supply ratio, supply variability, and selective grazing in the plankton: An experiment with a natural algal and protistan assemblage.
Authors: Grover James P.
Published: April 2010

Semicontinuous cultures were used to examine the effects of Si and P supply on a natural algal community. Three Si : P supply ratios were used, with different patterns of supply variability imposed by various schedules of Si and P pulses delivered 1, 4, or 10 d apart. All cultures with a given Si: P supply ratio received the same time‐averaged supply of Si and P. The Si: P supply ratio had a strong effect on the species composition of the algae. Chlorophytes were most abundant at the low Si: P supply ratio (20 : 1), diatoms were most abundant at the intermediate Si : P supply ratio (80 : 1), and the siliceous chrysophyte Mallomonas sp. was most abundant at the high Si : P supply ratio (160 : 1). Diatom species showed differentiation in their ability to compete for Si and P. On average, algal cells became smaller as the Si: P supply ratio decreased. Higher algal species richness was associated with increased variability in P supply. Competitive ability of some algae was increased by variability in P supply, but that of others was decreased.

A flagellated protist grazed selectively on two Nitzschia spp., and thereby altered their competitive dynamics. The biovolume of this protist, and that of other heterotrophic flagellates, decreased with increasing variability in P supply. Despite selective grazing and nutrient supply variability, patterns in the algal communities were generally consistent with expectations based on resource competition theory and previous experience with algal competition in cultures.
Multivariate statistical analysis of the factors controlling the distribution of scaled chrysophytes
Authors: Siver Peter A. , Hamer Josephine S.
Published: April 2010

A total of 332 collections from 62 water bodies was analyzed for scaled chrysophytes with electron microscopy and correlated with limnological characteristics. The pH and specific conductance were the most important factors controlling the distribution of scaled chrysophytes; temperature and total phosphorus were of lesser importance.

A mean of nine and seven taxa per collection were recorded at a pH of 5.5–6.0 and a specific conductance <40 µS, respectively. Significantly fewer taxa per collection were found as the pH lowered below 5.5 or raised above 6.0 or as the specific conductance increased above 40 S. Similar distributional patterns were found for the genera Mallomonas, Synura, and Spiniferomonas.

A two‐factor principal component model explained 70% of the total variance within the data set (n = 1,355). The first principal component explained 80 and 83% of the total variance within the pH and specific conductance variables. The pH and specific conductance also dominated the first principal component for each genus and for 23 of the 25 species tested. A cluster analysis, using within‐group linkages, produced five groups of organisms that differed primarily with respect to their distribution along a pH gradient.
Tidally induced estuarine phytoplankton patchiness
Authors: Dustan Phillip , Pinckney James L.
Published: April 2010

The patchiness of phytoplankton in Charleston Harbor, as measured by the distribution of chlorophyll a, is coupled to the periodicity of the tidal cycle. Phytoplankton aggregations occur at frontal zones that form on the flood when river and tidal flow are in opposition. The magnitude and variability of the chlorophyll distribution decrease during the ebb, and phytoplankton patches do not form at frontal zones. Tidal current velocities and not tidal heights appear to be the important ecological variables. This tidally driven periodic aggregation of phytoplankton represents an interaction between physical forcing functions and biological activity that may focus and locally intensify the trophodynamics of the pelagic component of the Charleston Harbor estuary. Tidally induced aggregation and subsequent offshore transport on the ebb may, in part, provide the mechanism that links the scale lengths of estuarine and coastal phytoplankton variability.
Dynamics of horizontal turbulent mixing in a nearshore zone of Lake Geneva
Authors: Lemmin U.
Published: April 2010

Time series of currents measured during the fall/winter period in a nearshore zone (near a headland and in an adjacent bay) of Lake Geneva, Switzerland, were used to determine horizontal turbulent mixing coefficients. The data were filtered to obtain components in the time range 0.5–12 h, which are suitable for mixing studies because spectra showed no energy source or system response there. From the filtered data, eddy diffusion coefficients were calculated by the integral time‐scale method and eddy viscosity coefficients by the Ertel mixing length method. Viscosity coefficients were systematically higher than diffusion coefficients by a factor of at least two. Longterm horizontal turbulent mixing coefficients calculated over periods of several months were of order 103 cm2 s 1, a factor of 10 lower than coefficients obtained for coastal zones of larger lakes. Short‐term (3 d) mixing coefficients varied between 102 cm2 s−1 for quiet background situations and 104 cm2 s−1 for periods of wind‐induced, large‐scale advection. This variability was traced to the history of wind events, indicating that energy input is not sufficiently homogeneous in time to maintain mixing at a constant level. Sheltering by local topography caused the sensitivity of the mixing coefficients to wind direction. Variability in space, with larger values at the headland and smaller ones inside the bay, underlined the modifying influence of shoreline geometry. Inside the bay, diffusion diagrams show that near the surface mixing is generated by shear, while near the bottom inertial subrange diffusion is found. The importance of shear is also evidenced by a correlation between wind forcing and diffusion coefficients for events of long wind fetch. Near the headland none of these simple concepts hold because local topography influences mixing.
An oxygen microsensor with a guard cathode
Authors: Revsbech Niels Peter
Published: April 2010

A new oxygen microsensor has an internal guard cathode that removes all oxygen diffusing toward the sensor from the internal electrolyte. It exhibits unprecedented signal stability and is easy to construct. The high stability may make the use of such microsensors advantageous for routine environmental applications.
Simulation of bacterial attraction and adhesion to falling particles in an aquatic environment
Authors: Jackson George A.
Published: April 2010

Chemosensory movement of bacteria toward the cloud of leaked material around planktonic algae has been suggested as an important aspect of bacterial nutrition in aquatic ecosystems. Inability of bacteria to keep pace with falling algae has been suggested as inhibiting such interactions. The interaction between bacteria and falling particles, including microalgae, is explored with a simulation model of bacterial chemotaxis that incorporates low Reynolds number fluid flow and resulting substrate spatial distributions. Results show that although bacteria cannot maintain a position relative to a falling particle unless the particle is extremely large, such as a marine snow aggregate, chemosensory response does allow them to stay in the high substrate environment of the leaky particle longer than if they did not have it. The ecological significance for bacterial metabolism depends on several factors, including the frequency of contact between algae and bacteria and the relative concentrations of substrate at the cell surface and in the background. Optimal enhancement should occur in eutrophic conditions of large algal cells present in high abundances. Presently available values for the ratio of substrate concentration next to the algal cell relative to that in solution are not large enough to suggest that the microzones around algal cells provide significant enhancement of bacterial nutrition.

Chemotaxis should enhance interactions with large marine snow aggregates, both by allowing bacteria to stay for significant periods around them and by enhancing the rates at which bacteria attach to the aggregate surfaces. This enhancement is greater for surfaces in which there is a lower probability of sticking.
The measurement and distribution of dissolved nucleic acids in aquatic environments
Authors: Karl David M. , Bailiff Megan D.
Published: April 2010

Nucleic acids (DNA and RNA) are ubiquitous components of the dissolved organic matter (DOM) pool of all oceanic, neritic, estuarine, and freshwater habitats studied to date. A new method for the quantitative determination of dissolved nucleic acids (DNA and RNA) in water and sediment samples was developed, evaluated, and utilized in a study of various marine and freshwater ecosystems. Under appropriate reaction conditions, dissolved DNA (D‐DNA) and dissolved RNA (D‐RNA) are efficiently removed from solution with the addition of cetyltrimethylammonium bromide (CTAB) and subsequent formation of insoluble CTA‐nucleic acid salts. The insoluble salts are collected, by filtration, onto glass‐fiber filters and analyzed for DNA and RNA with fluorometric and colorimetric procedures, respectively. The performance of this CTAB method is simple, reliable, and reproducible for measuring dissolved nucleic acids in natural aquatic environments. For the ecosystems investigated herein, D‐DNA and D‐RNA concentrations ranged from 0.56 to 88 µg liter−1 and 4.03 to 871 µg liter−1; the ratio of D‐RNA to D‐DNA ranged from 4.1 to 11.5.
The effect of Daphnia interference on a natural rotifer and ciliate community: Short‐term bottle experiments
Authors: Gilbert John J.
Published: April 2010

Two bottle experiments were conducted using water from a small, eutrophic lake to assess the impact of Daphnia interference (encounter) competition on the dynamics of the rotifer and ciliate populations dominating the zooplankton community. Indirect effects of Daphnia exploitative competition were minimized by adding food resources and using short incubation periods. The introduction of Daphnia pulex (16 liter−1) to Cryptomonas‐enriched (3–3.5 × 104 cells ml−1) water for 2 d significantly suppressed numbers of the ciliate Campanella sp.; the rotifers Kellicottia bostoniensis, Keratella cochlearis, Keratella crassa, Polyarthra vulgaris, and Synchaeta pectinata; and total rotifers. The presence of Daphnia did not affect numbers of the rotifers Asplanchna girodi, Polyarthra euryptera, and Trichocerca similis. Daphnia‐induced death rates of significantly suppressed, common species were highest for K. cochlearis (0.79–1.14 d−1), intermediate for S. pectinata and Campanella (0.23–0.33 d−1), and lowest for K. crassa and P. vulgaris (0.14–0.28 d−1). The most marked effects of Daphnia on community structure were 61–77% reductions in the relative abundance of K. cochlearis and up to 100% increases in the relative abundances of K. crassa and T. similis. The observed effects of Daphnia on the rotifer species are consistent with, and largely explicable by, previously conducted laboratory experiments and behavioral observations on interference between Daphnia and these or closely related species. Interference from Daphnia can rapidly reduce the abundance and shift the species structure of rotifer and ciliate assemblages in natural communities.
Swimming behavior of krill in response to algal patches: A mesocosm study
Authors: Price Holly J.
Published: April 2010

An understanding of the response of zooplankton to phytoplankton patches is required to determine the relative importance of behavior vs. physical dynamics in generating and maintaining zooplankton aggregations. The swimming behavior of the krill Thysanoessa raschii was monitored with dual video cameras in a 117‐m3 tank before and after the introduction of a subsurface algal patch. Krill density within the patch was an order of magnitude higher than the control density within 0.5 h after algal introduction, suggesting krill have some means of detecting and remaining within a concentrated food source. Orientation of the swimming paths became more horizontal, swimming speed doubled, and sinking bouts were almost entirely eliminated inside the algal patch. The net‐to‐gross displacement ratio of the swimming paths indicated no increase in looping or spiraling. However, individual krill kept themselves within the patch by turning back at the boundary so that the angle of approach to and return from the edge was held roughly constant. The behavioral changes shown by T. raschii within the algal patch were maintained over the 24‐h period following its introduction. The ability to detect and remain within algal patches must be considered in explanations of euphausiid distribution and in the construction of more realistic energy budgets.
Effects of flocculated humic matter on free and attached pelagic microorganisms
Authors: Tranvik Lars J. , Sieburth John McN.
Published: April 2010

The effect of dissolved and particulate humic matter on pelagic microorganisms was studied in laboratory experiments. A humic concentrate was added to cultures of natural bacterial populations in either dissolved or partly flocculated form. Due to the occurrence of epibacteria attached to particles, a markedly higher bacterial yield was obtained when a fraction of the added carbon was flocculated. Attached bacteria apparently utilized flocs as well as dissolved organic carbon surrounding the particles. Both free and attached bacteria were grazed by phagotrophic flagellates. In addition to grazing attached bacteria, attached flagellates could ingest free bacteria. In 11 oligotrophic lakes, ranging from those with clear water to those heavily colored with humic substances, a linearly increasing amount of both particulate material and particle‐associated epibacteria was found in the pelagial with increasing humic content. We suggest that suspended detritus particles (humic flocculates) have a positive influence on the secondary productivity of humic lakes due to an enrichment of the heterotrophic epibacterial‐bacterivorous flagellate segment of the microbial food web.
Whole‐lake experiments: The annual record of fossil pigments and zooplankton
Authors: Leavitt P. R. , Carpenter S. R. , Kitchell J. F.
Published: April 2010

The annual record of fossil pigments and zooplankton was compared with detailed contemporaneous records from two manipulated lakes from 1940 to 1986. Annually resolved sedimentary records accurately monitored known changes inplankton communities, identified periods of trophic change, and proved a powerful tool for examining long‐term, complex interactions. Both Paul and Peter Lakes underwent the same three complete changes in their fish assemblages (trout, cyprinid, bass), and Peter Lake received repeated inputs of lime. Alterations in fish community composition produced long‐lived changes in zooplankton communities that cascaded to the microbial level of the food web. Liming, in concert with trophic changes, caused distinctive phytoplankton dynamics in Peter Lake.

Paleolimnological data recorded all major plankton dynamics known from coeval limnological data. Specifically, the sediment record showed transitions in cladoceran size structure and species composition, changes in water clarity resulting from both food web and chemical manipulations that affected vertical zonation of primary producers, and changes in absolute abundance of all algal divisions except dinoflagellates. Undegraded Chl a indicated deep blooms and, in conjunction with Chl c, fucoxanthin and β‐carotene, indicated metalimnetic chrysophytes. Transient (2–3 yr) nonselective increases in sedimentation corresponded with increases in grazing rates. Isorenieratene indicated overlap of photic and anoxic zones, revealing changes in transparency and conditions for pigment preservation.
Diel fluctuations in bacterial activity on streambed substrata during vernal algal blooms: Effects of temperature, water chemistry, and habitat
Authors: Kaplan Louis A. , Bott Thomas L.
Published: April 2010

Diel fluctuations in stream water temperature and chemistry, microbial biomass, and bacterial activity were measured in White Clay Creek, Pennsylvania, during vernal algal blooms in three different years. DOC concentrations increased 24–37% over early morning minima and temperature increased nearly 10°C over a 7–10‐h period. Total carbohydrates and monosaccharides exhibited irregular fluctuations with total carbohydrates showing concentration peaks in the morning and afternoon. Acetate concentrations were highest in midafternoon, while the concentration pattern for primary amines differed from the DOC pattern with highest values at midnight. No distinct diel patterns were found for streambed ATP, : ATP, Chl a, and total or active bacteria, although significant year‐to‐year and between‐habitat differences were observed. Bacterial activity, measured by phospholipid biosynthesis, total lipid biosynthesis, respiration, and incorporation of [3H]thymidine into DNA increased 1.4‐fold to 3.0‐fold from morning to afternoon. Microcosm experiments indicated that the activity of bacteria attached to sediments was more sensitive to increases in water temperature than to changes in water chemistry, whereas bacteria attached to porcelain disks responded to the influences of both temperature and water chemistry.