bluuebunny/crossref_metadata_2025 huggingface dataset:
Stereoselective synthesis of four possible isomers of streptopyrrolidine
Authors: Mohapatra Debendra K , Thirupathi Barla , Das Pragna P , Yadav Jhillu S
Published: January 2011

The synthesis of (4R,5R)-streptopyrrolidine (1), (4S,5R)-streptopyrrolidine (2) (4R,5S)-streptopyrrolidine (3) and (4S,5S)-streptopyrrolidine (4) have been achieved in a concise and highly efficient manner via a highly stereoselective aldol type reaction with the trimethylsilyl enolate of ethyl acetate and Lewis acid mediated lactamization as the key reactions in ≈42% yield over six steps starting from D-phenylalanine and L-phenylalanine, respectively. The absolute configuration of the natural product was shown to be (4S,5S) by comparing its spectral and analytical data with the reported values.
INTEGRATED DSS FOR STRATEGIC PLANNING IN PUBLIC INSTITUTIONS
Authors: Tunčikienė Živilė , Bivainis Juozas , Drejeris Rolandas
Published: January 2011

The paper deals with a problem of support to the strategic planning decision‐making in public institutions. In special literature there are various approaches proposed to what decision support system (DSS) is rational to use in management area. This diversity is determined by the nature of management problems, goals and the chosen approaches for achieving the goals. In order to prepare the approaches which are necessary to carryout the strategic planning in the institutions, the role of the DSS was revealed, the structure of the system was defined, and the variety of the DSS was systematized. Besides, the factors which predetermine the requirements for the DSS of strategic planning in the institutions were defined. According to these factors and the results of the research on theoretical potential of decision support, it is rational to apply a complex character of intelligent support to prepare alternatives and to make decisions of strategic planning in public institutions. The authors have based a solution with regard to the integrated DSS for the strategic planning. Santrauka Straipsnyje nagrinejama viešojo sektoriaus instituciju strateginio planavimo sprendimu paramos problematika. Specialiojoje literatūroje pateikiami skirtingi požiūriai i tai, kokia sprendimu paramos sistema (toliau – SPS) racionalu taikyti valdymo problemoms spresti. Tokia ivairove lemia nagrinejamu valdymo problemu, kartu keliamu tikslu ir ju igyvendinimo nuostatu pobūdis. Siekiant parengti viešojo sektoriaus instituciju strateginiam planavimui reikalingos SPS principines nuostatas, atskleistas SPS vaidmuo, apibrežta pagrindinems SPS funkcijoms igyvendinti būtina sistemos struktūra, susistemintos SPS atmainu savybes. Be to, nustatyti veiksniai, kurie lemia reikalavimus, keliamus viešojo sektoriaus instituciju strateginio planavimo SPS. Atsižvelgiant i tokius veiksnius ir sprendimu paramos teorinio potencialo nagrinejimo rezultatus, numatyta skirtinga pagal pobūdi intelektine parama viešojo sektoriaus instituciju strateginio planavimo sprendimams rengti ir priimti, pagristas sprendimas del integruotos strateginio planavimo SPS.
A method for continuous rearing of grapevine leafhoppers,Erythroneuraspp. (Hemiptera: Cicadellidae)
Authors: Saguez J. , Vincent C.
Published: January 2011

We report a two-step method to rear three leafhopper species,Erythroneura elegantulaOsborn,Erythroneura vitis(Harris), andErythroneura ziczacWalsh, for experimental purposes on grapevines. The first step involves rearing adults on grapevines for reproduction, oviposition, and egg development. The second step involves rearing nymphs on isolated leaves placed in Petri dishes lined with agar. No mortality was observed and adults emerged in about three weeks. The threeErythroneuraspecies were reared for 10 consecutive generations with minimal resources.
Increased Nitric Oxide and Attenuated Diastolic Blood Pressure Variability in African Americans with Mildly Impaired Renal Function
Authors: Diaz Keith M. , Feairheller Deborah L. , Sturgeon Kathleen M. , Veerabhadrappa Praveen , Williamson Sheara T. , Crabbe Deborah L. , Brown Michael D.
Published: January 2011

We investigated the relationship between renal function, blood pressure variability (BPV), and nitric oxide (NO) in a group of African Americans with normal or mildly impaired renal function. 24-hour ambulatory blood pressure monitoring was performed, NO measured, and glomerular filtration rate (GFR) calculated in 38 African Americans. Participants were categorized as having normal (GFR > 90 mL/min per 1.73 m2) or mildly impaired (GFR 60–89 mL/min per 1.73 m2) renal function. Diastolic BPV was significantly lower in the mildly impaired renal function group. Regression analyses revealed a significant positive association between GFR and diastolic BPV for the entire study group. Plasma NO levels were significantly higher in the mildly impaired renal function group and negatively correlated with diastolic BPV. In conclusion, diastolic BPV was reduced in African Americans with mildly impaired renal function, which may be the result of increased NO production. These results conflict with previous findings in diseased and nonblack populations and could provide rationale for studying BPV early in the disease state when BP-buffering mechanisms are still preserved.
Preparation of Antioxidant Enzymatic Hydrolysates from Honeybee-Collected Pollen Using Plant Enzymes
Authors: Marinova Margarita D. , Tchorbanov Bozhidar P.
Published: January 2011

Enzymatic hydrolysates of honeybee-collected pollen were prepared using food-grade proteinase and aminopeptidases entirely of plant origin. Bromelain from pineapple stem was applied (8 mAU/g substrate) in the first hydrolysis stage. Aminopeptidase (0.05 U/g substrate) and proline iminopeptidase (0.03 U/g substrate) from cabbage leaves (Brassica oleraceavar.capitata), and aminopeptidase (0.2 U/g substrate) from chick-pea cotyledons (Cicer arietinumL.) were involved in the additional hydrolysis of the peptide mixtures. The degree of hydrolysis (DH), total phenolic contents, and protein contents of these hydrolysates were as follows: DH (about 20–28%), total phenolics (15.3–27.2 μg/mg sample powder), and proteins (162.7–242.8 μg/mg sample powder), respectively. The hydrolysates possessed high antiradical scavenging activity determined with DPPH (42–46% inhibition). The prepared hydrolysates of bee-collected flower pollen may be regarded as effective natural and functional dietary food supplements due to their remarkable content of polyphenol substances and significant radical-scavenging capacity with special regard to their nutritional-physiological implications.
A Modified Porous Titanium Sheet Prepared by Plasma-Activated Sintering for Biomedical Applications
Authors: Tamaki Yukimichi , Lee Won Sik , Kataoka Yu , Miyazaki Takashi
Published: January 2011

This study aimed to develop a contamination-free porous titanium scaffold by a plasma-activated sintering within an originally developed TiN-coated graphite mold. The surface of porous titanium sheet with or without a coated graphite mold was characterized. The cell adhesion property of porous titanium sheet was also evaluated in this study. The peak of TiC was detected on the titanium sheet processed with the graphite mold without a TiN coating. Since the titanium fiber elements were directly in contact with the carbon graphite mold during processing, surface contamination was unavoidable event in this condition. The TiC peak was not detectable on the titanium sheet processed within the TiN-coated carbon graphite mold. This modified plasma-activated sintering with the TiN-coated graphite mold would be useful to fabricate a contamination-free titanium sheet. The number of adherent cells on the modified titanium sheet was greater than that of the bare titanium plate. Stress fiber formation and the extension of the cells were observed on the titanium sheets. This modified titanium sheet is expected to be a new tissue engineering material in orthopedic bone repair.
The Pathological Roles of Ganglioside Metabolism in Alzheimer′s Disease: Effects of Gangliosides on Neurogenesis
Authors: Ariga Toshio , Wakade Chandramohan , Yu Robert K.
Published: January 2011

Conversion of the soluble, nontoxic amyloid β‐protein (Aβ) into an aggregated, toxic form rich in β‐sheets is a key step in the onset of Alzheimer′s disease (AD). It has been suggested that Aβ induces changes in neuronal membrane fluidity as a result of its interactions with membrane components such as cholesterol, phospholipids, and gangliosides. Gangliosides are known to bind Aβ. A complex of GM1 and Aβ, termed “GAβ”, has been identified in AD brains. Abnormal ganglioside metabolism also may occur in AD brains. We have reported an increase of Chol‐1α antigens, GQ1bα and GT1aα, in the brain of transgenic mouse AD model. GQ1bα and GT1aα exhibit high affinities to Aβs. The presence of Chol‐1α gangliosides represents evidence for genesis of cholinergic neurons in AD brains. We evaluated the effects of GM1 and Aβ1–40 on mouse neuroepithelial cells. Treatment of these cells simultaneously with GM1 and Aβ1–40 caused a significant reduction of cell number, suggesting that Aβ1–40 and GM1 cooperatively exert a cytotoxic effect on neuroepithelial cells. An understanding of the mechanism on the interaction of GM1 and Aβs in AD may contribute to the development of new neuroregenerative therapies for this disorder.
Clinical Interaction between Brain and Kidney in Small Vessel Disease
Authors: Mogi Masaki , Horiuchi Masatsugu
Published: January 2011

Patients with chronic kidney disease (CKD) are well known to have a higher prevalence of cardiovascular disease from epidemiological studies. Recently, CKD has also been shown to be related to neurological disorders, not only ischemic brain injury but also cognitive impairment. This cerebrorenal connection is considered to involve small vessel disease in both the kidney and brain, based on their hemodynamic similarities. Clinical studies suggest that markers for CKD such as estimated glomerular filtration rate (eGFR), proteinuria, and albuminuria may be helpful to predict brain small vessel disease, white matter lesions (WMLs), silent brain ischemia (SBI), and microhemorrhages. Recently, changes in the vascular system of the brain have been shown to contribute to the onset and progression of cognitive impairment, not only vascular dementia but also Alzheimer's disease. Patients with CKD are also reported to have higher risk of impaired cognitive function in the future compared with non-CKD subjects. These results indicate that CKD markers may be helpful to predict the future risk of neuronal disease.
Basal-Like Phenotype in a Breast Carcinoma Case Series from Sudan: Prevalence and Clinical/Pathological Correlations
Authors: Awadelkarim Khalid Dafaallah , Arizzi Carmelo , Elamin Elgizouli Omer Musa , Hamad Hussein M. A. , De Blasio Pasquale , Mekki Salwa O. , Osman Ihsan , Biunno Ida , Elwali Nasr Eldin , Barberis Massimo Costanzo , Mariani-Costantini Renato
Published: January 2011

Basal-like breast cancer, an aggressive subtype associated with high grade, poor prognosis, and younger age, is reported frequently in Africa. We analyzed the expression of the basal cytokeratins (CKs) 5/6 and 17 in a case series from Central Sudan and investigated correlations among basal CK status, ER, PgR, and Her-2/neu, and individual/clinicopathological data. Of 113 primary breast cancers 26 (23%), 38 (34%), and 46 (41%) were, respectively, positive for CK5/6, CK17, and combined basal CKs (CK5/6 and/or CK17). Combined basal CK+ status was associated with higher grade (P<.03) and inversely correlated with ER (P<.002), PgR (P=.004) and combined ER and/or PgR (P<.0002). Two clusters based on all tested markers were generated by hierarchical cluster analysis and k-mean clustering: I: designated ``hormone receptors positive/luminal-like’’ and II: designated ``hormone receptors negative’’, including both basal-like and Her-2/neu+ tumors. The most important factors for dataset variance were ER status, followed by PgR, CK17, and CK5/6 statuses. Overall basal CKs were expressed in a fraction of cases comparable to that reported for East and West African case series. Lack of associations with age and tumor size may represent a special feature of basal-like breast cancer in Sudan.
Lifestyle Practices and Cardiovascular Disease Mortality in the Elderly: The Leisure World Cohort Study
Authors: Paganini-Hill Annlia
Published: January 2011

Modifiable behavioral risk factors are major contributing causes of death, but whether the effects are maintained in older adults is uncertain. We explored the association of smoking, alcohol consumption, caffeine intake, physical activity, and body mass index on cardiovascular disease (CVD) mortality in 13,296 older adults and calculated risk estimates using Cox regression analysis in four age groups (<70, 70–74, 75–79, and 80+ years). The most important factor was current smoking, which increased risk in all age-sex groups. In women, alcohol consumption (≤3 drinks/day) was related to decreased (15–30%) risk in those <80 years old; in men, 4+ drinks/day was associated with reduced (15–30%) risk. Active 70+ year olds had 20–40% lower risk. Both underweight and obese women were at increased risk. Lifestyle practices impact CVD death rates in older adults, even those aged 80+ years. Not smoking, moderate alcohol consumption, physical activity, and normal weight are important health promoters in our aging population.
CO2 control of Trichodesmium N2 fixation, photosynthesis, growth rates, and elemental ratios: Implications for past, present, and future ocean biogeochemistry
Authors: Hutchins D. A. , Fu F.-X. , Zhang Y. , Warner M. E. , Feng Y. , Portune K. , Bernhardt P. W. , Mulholland M. R.
Published: January 2011

Diazotrophic marine cyanobacteria in the genus Trichodesmium contribute a large fraction of the new nitrogen entering the oligotrophic oceans, but little is known about how they respond to shifts in global change variables such as carbon dioxide (CO2) and temperature. We compared Trichodesmium dinitrogen (N2) and CO2 fixation rates during steady‐state growth under past, current, and future CO2 scenarios, and at two relevant temperatures. At projected CO2 levels of year 2100 (76 Pa, 750 ppm), N2 fixation rates of Pacific and Atlantic isolates increased 35–100%, and CO2 fixation rates increased 15‐128% relative to present day CO2 conditions (39 Pa, 380 ppm). CO2‐mediated rate increases were of similar relative magnitude in both phosphorus (P)‐replete and P‐limited cultures, suggesting that this effect may be independent of resource limitation. Neither isolate could grow at 15 Pa (150 ppm) CO2, but N2 and CO2 fixation rates, growth rates, and nitrogen : phosophorus (N : P) ratios all increased significantly between 39 Pa and 152 Pa (1500 ppm). In contrast, these parameters were affected only minimally or not at all by a 4°C temperature change. Photosynthesis versus irradiance parameters, however, responded to both CO2 and temperature but in different ways for each isolate. These results suggest that by the end of this century, elevated CO2 could substantially increase global Trichodesmium N2 and CO2 fixation, fundamentally altering the current marine N and C cycles and potentially driving some oceanic regimes towards P limitation. CO2 limitation of Trichodesmium diazotrophy during past glacial periods could also have contributed to setting minimum atmospheric CO2 levels through downregulation of the biological pump. The relationship between marine N2 fixation and atmospheric CO2 concentration appears to be more complex than previously realized and needs to be considered in the context of the rapidly changing oligotrophic oceans.
Nitrogen fixation along a north‐south transect in the eastern Atlantic Ocean
Authors: Staal Marc , te Lintel Hekkert Sacco , Jan Brummer Geert , Veldhuis Marcel , Sikkens Cor , Persijn Stefan , Stal Lucas J.
Published: January 2011

Nitrogenase activity, indicative of N2 fixation, was measured in the surface waters along a north‐south transect in the eastern Atlantic Ocean, from Texel (The Netherlands, 53°N) to Cape Town (South Africa, 35°S) using a sensitive on‐line, near real‐time acetylene reduction assay. From the beginning of January to the end of February 2000 nitrogenase activity was detected in varying rates, but only between 14°N and 13°S latitudes. Dark incubations yielded an average activity of 2.2 (± 2.4) µmol m−2 d−1 N, but light increased the activity to 3.7 (± 2.9) µmol m−2 d−1 N. However, nitrogenase activity in the light was sensitive to O2 doubling to 7.6 (± 12.7) µmol m−2 d−1 N when the incubation was anaerobic. In the area where N2 fixation occurred, phosphate concentrations were fourfold lower than in the area where N2 fixation was absent, while silicate levels were higher. The water temperature in the area with N2 fixation was 28°C, while in the adjacent area the temperature was 3°C lower, which might have prevented the proliferation of diazotrophic cyanobacteria. Action spectra revealed that chlorophyll a, phycocyanin, and phycoerythrin are the light‐harvesting pigments supporting nitrogenase activity. In one area in the northern latitudes, potential nitrogenase activity was highest during daytime, which is characteristic for Trichodesmium. In areas with a high potential nitrogenase activity, surface waters were dominated by a phycoerythrin‐containing cyanobacterium. Since nitrogenase activities were highest at night, these cells may have been unicellular cyanobacteria like Crocosphaera.
Nitrogen fixation by unicellular diazotrophic cyanobacteria in the temperate oligotrophic North Pacific Ocean
Authors: Needoba Joseph A. , Foster Rachel A. , Sakamoto Carole , Zehr Jonathan P. , Johnson Kenneth S.
Published: January 2011

N2 fixation has been understudied in marine environments outside of the subtropical and tropical oceans and where water temperatures are typically below 20‐25°C. We identified nifH phylotypes and measured N2 fixation rates under ambient conditions (maximum of 19°C) in water collected 750 km off the coast of California in oligotrophic waters of the North Pacific Ocean (34°N, 129°W). Near‐surface N2 fixation rates averaged 0.25 ± 0.05 nmol N L−1 d−1 for 24 incubation bottles. Despite low ambient concentrations of iron (<0.1 nmol L−1) and phosphorus (<0.3 µmol L−1), N2 fixation rates were unaffected by iron and phosphorus amendments. Using reverse transcription‐quantitative polymerase chain reaction (RT‐QPCR) methodology, we estimated transcript abundance and patterns of expression for several unicellular diazotrophs, including the group A phylotype, which showed the highest daily mRNA abundances. The N2‐fixing assemblage extended to 60‐80 m depth, well below the seasonal thermocline (40 m). The calculated areal N2 fixation rate (15 µmol N m−2 d−1) was small compared with estimates from other regions of the Pacific; however, the estimated fixation rate was similar to other published results, suggesting that processes other than cellular growth rate may determine the abundance of unicellular diazotrophs. Despite the low N2 fixation rates, the new nitrogen added to the euphotic zone by N2 fixation could account for at least 10% of new production during the study period.
Biogeochemical budgets in the eastern boundary current system of the North Atlantic: Evidence of net heterotrophy and nitrogen fixation
Authors: Álvarez Marta , Álvarez-Salgado XosÉ Antín
Published: January 2011

Thermohaline and chemical data from three WOCE (World Ocean Circulation Experiment) cruises conducted in 1997 and 1998 define the MedBox region, bounded by the Strait of Gibraltar, 24°N, 41°N, and 22°W. The carbon budget indicates that the MedBox is a heterotrophic region, where carbon is mineralized at a net rate of 17 ± 11 g C m−2 yr−1, supported by the input of allochthonous organic matter, mainly in the dissolved form, from the adjacent ocean. Dissolved organic carbon accounts for 90% of the organic carbon demand. In vitro measurements to estimate the net community production of the study area differ largely from our geochemical budget estimation, likely reflecting different spatial and temporal scales and/or terms or processes not taken into account by both methods. The nitrogen budget of the MedBox pointed to a significant atmospheric input via N2 fixation (3.4 ± 3.1 g N m−2 yr−1).
Shift from denitrification to anammox after inflow events in the central Baltic Sea
Authors: Hannig M. , Lavik G. , Kuypers M. M. M. , Woebken D. , Martens-Habbena W. , JÜrgens K.
Published: January 2011

Incubation experiments with 15N‐labeled compounds (NO3− and NH4+) were performed during three cruises (2002, 2004, and 2005) to study the loss of inorganic N as dinitrogen gas (N2) via denitrification and anammox in the water column of the Gotland Deep (central Baltic Sea). 15N incubations did not provide evidence for direct conversion of NO3− reduction to N2 (heterotrophic denitrification) in the suboxic (O2 < 10 µmol L−1) sulfide‐free waters. Substantial denitrification rates (up to 2.7 µmol L−1 d−1 N2) were measured in water samples collected from the NO3−‐H2S interface (redoxcline) in 2002 and in water from the sulfidic zone in 2004, which indicates chemolithotrophic denitrification as the dominant N‐loss process in both years. Massive inflows of oxygenated North Sea water from 2002 to 2003 caused a complete ventilation of the Baltic Sea with high oxygen concentrations in the Gotland Deep bottom water. After the reestablishment of the redoxcline in 2004, a newly formed suboxic zone above sulfidic waters—with NO3−, NO2−, and NH4+ at the detection limit—was observed in spring 2005. The development of this zone was associated with a several‐fold increase in reduced and oxidized manganese and with a shift from denitrification to anammox as the main N‐loss process. Fluorescence in situ hybridization analysis confirmed the presence of anammox bacteria and the number of anammox cells was consistent with the observed N2 production rates in 2005.
Nitrate‐depleted conditions on the increase in shallow northern European lakes
Authors: Weyhenmeyer Gesa A , Jeppesen Erik , Adrian Rita , Arvola Lauri , Blenckner Thorsten , Jankowski Thomas , Jennings Eleanor , Nõges Peeter , Nõges Tiina , Straile Dietmar
Published: January 2011

We determined relative nitrate‐nitrogen (NO3‐N) loss rates in 100 north‐mid‐European lakes from late spring to summer by using the exponential function N2 = N1e−k(t2−t2), where N1 and N2 are NO3‐N concentrations at the beginning (t1) and the end (t2) of the time interval, respectively, and k is the specific NO3‐N loss rate. We found that k decreased with increasing lake depth. Adjusting k to the lake depth (kadj), we observed that kadj was positively related to spring NO3‐N concentrations, but this relationship became insignificant at mean lake depths exceeding 12.5 m. A relationship between kadj and spring NO3‐N concentrations in lakes shallower than 12.5 m implies that changes in spring NO3‐N concentrations influence the NO3‐N loss rate and thereby summer NO3‐N concentrations. Time series from one Estonian, one German, and 14 Swedish lakes shallower than 12.5 m since 1988 revealed that May to August NO3‐N concentrations have decreased over time everywhere, and the number of time periods exhibiting a NO3‐N depleted condition, i.e., NO3‐N levels below 10 mg L−1, in these lakes has tripled since 1988. We explained the decreasing NO3‐N concentrations by a reduction in external nitrogen loading including atmospheric deposition, and by changes in climate. The observed prolongation of NO3‐N depleted conditions might be one possible explanation for the increasing occurrence of nitrogen‐fixing cyanobacteria in a variety of lake ecosystems.
Potential role of copper availability in nitrous oxide accumulation in a temperate lake
Authors: Twining Benjamin S. , Mylon Steven E. , Benoit Gaboury
Published: January 2011

Denitrifying bacteria require copper for the synthesis of nitrous oxide reductase. In the absence of sufficient bioavailable Cu, nitrous oxide (N2O) may accumulate in natural waters during denitrification. Cultures of Paracoccus denitrificans and natural bacterial assemblages collected from a mesotrophic lake (Linsley Pond) were grown at varying Cu concentrations to determine the Cu speciation that results in elevated N2O accumulation. P. denitrificans experienced Cu limitation beginning at inorganic Cu concentrations of 0.6 fmol L−1 (−log of inorganic Cu, pCu′, = 15.2). The natural community did not show an effect until pCu′ was reduced to 23.7 with 8‐hydroxyquinoline, resulting in an approximate 10‐fold increase in N2O concentrations during denitrification. Additions of ethylenediaminetetraacetic acid alone to natural communities did not affect N2O concentrations. Natural copper‐binding ligands detected with competitive ligand exchange‐cathodic stripping voltammetry occurred at concentrations of 6 to 25 nmol L21 with conditional stability constants (KCu2+ L) between 1014.4 and 1015.1. Although more than 99% of total Cu in Linsley Pond was bound to these ligands, inorganic Cu concentrations remained 10 orders of magnitude above those found to increase N2O accumulation during denitrification incubations. Measurements of nitrogen species, dissolved oxygen, and sulfide in the water column of Linsley Pond over the spring growing season revealed that N2O was produced by assimilatory nitrate reduction and nitrification in addition to denitrification, with nitrification generating most of the N2O found in the surface waters of the lake. The results suggest that inorganic Cu concentrations in Linsley Pond are sufficient to support denitrification. Moreover, some denitrifying bacteria may be able to access organically bound Cu, reducing the potential for this metal to affect N2O production in other aquatic environments.
Biogas (CO2, O2, dimethylsulfide) dynamics in spring Antarctic fast ice
Authors: Delille Bruno , Jourdain Bruno , Borges Alberto V. , Tison Jean-Louis , Delille Daniel
Published: January 2011

We studied the temporal variations of CO2, O2, and dimethylsulfide (DMS) concentrations within three environments (sea‐ice brine, platelet ice‐like layer, and underlying water) in the coastal area of Adeélie Land, Antarctica, during spring 1999 before ice breakup. Temporal changes were different among the three environments, while similar temporal trends were observed within each environment at all stations. The underlying water was always undersaturated in O2 (around 85%) and oversaturated in CO2 at the deepest stations. O2 concentrations increased in sea‐ice brine as it melted, reaching oversaturation up to 160% due to the primary production by the sea‐ice algae community (chlorophyll a in the bottom ice reached concentrations up to 160 µg L−1 of bulk ice). In parallel, DMS concentrations increased up to 60 nmol L21 within sea‐ice brine and the platelet ice‐like layer. High biological activity consumed CO2 and promoted the decrease of partial pressure of CO2 (pCO2). In addition, melting of pure ice crystals and calcium carbonate (CaCO3) dissolution promoted the shift from a state of CO2 oversaturation to a state of marked CO2 undersaturation (pCO2 < 30 dPa). On the whole, our results suggest that late spring land fast sea ice can potentially act as a sink of CO2 and a source of DMS for the neighbouring environments, i.e., the underlying water or/and the atmosphere.
Chemical and physical speciation of mercury in Offatts Bayou: A seasonally anoxic bayou in Galveston Bay
Authors: Han Seunghee , Lehman Ronald D. , Choe Key-Young , Gill Gary A.
Published: January 2011

A chemical equilibrium model was used to predict the solution speciation of dissolved mercury (Hg) in the stratified water column of Offatts Bayou, a subestuary in Galveston Bay, Texas, which undergoes seasonal anoxia in bottom waters. Chemical equilibrium modeling was conducted using conditional stability constants and concentrations of Hg‐complexing organic ligands experimentally determined by competitive ligand equilibration methods. Dissolved Hg complexation was dominated by interactions with sulfide and dissolved organic matter (DOM) (HOHgHS0, HOHgHS(DOM), HgSHS−, and HgS22‐ at all depths. Sulfide and glutathione competed for methylmercury (MeHg) complexation in oxic layers; in anoxic waters, sulfide complexation dominated MeHg speciation. The particle‐water distribution coefficient (Kd) of Hg decreased in the anoxic layer of the water column, where the dissolved sulfide concentration increased, providing evidence that sulfide complexation influences the solubility of Hg. The solubility of MeHg was elevated in the anoxic as compared to the oxic layers, and this distributional feature was coincident with a change in the solution speciation of dissolved MeHg from glutathione/sulfide complexation in the oxic layers to a predominantly sulfide complexation in the anoxic layers. Maximum enrichment of Hg, MeHg, and iron (Fe) in suspended particulate matter was observed in the lower layer of the pycnocline, most likely resulting from formation of insoluble Fe oxide, which scavenged dissolved Hg‐sulfide and MeHg‐sulfide species. The concomitant decrease in dissolved inorganic Hg, Fe, and sulfide in the anoxic layers is suggested to result from scavenging of inorganic Hg by FeS, which is in accordance with the Hg speciation model. Overall, Hg cycling in the water column of Offatts Bayou was associated with sulfide and DOM complexation, Fe dissolution/precipitation, water column production of MeHg, and/or efflux of MeHg from anoxic sediment.
Characterization of methanogenic Archaea and stable isotope fractionation during methane production in the profundal sediment of an oligotrophic lake (Lake Stechlin, Germany)
Authors: Conrad Ralf , Chan On-Chim , Claus Peter , Casper Peter
Published: January 2011

The methanogenic archaeal community, methane production, and carbon isotopic fractionation were studied in the profundal sediments of oligotrophic Lake Stechlin. Because the water column of oligotrophic lakes is usually oxic, CH4 is normally not produced in the sediment surface layers. Nevertheless, 16S rRNA gene sequences of both acetoclastic Methanosaeta spp. and hydrogenotrophic Methanomicrobiales were detected, and potential CH4 production (assayed at 30°C) was much higher at the surface (0‐5 cm) than in the deeper (20‐ 25 cm) sediment layers, albeit starting only after sulfate was reduced. Copy numbers of the bacterial 16S rRNA genes were also higher in the surface than in the deeper sediment layers, but those of archaeal 16S rRNA genes were similar. Hydrogenotrophic and acetoclastic methanogenesis contributed equally to methane production, as quantified by a comprehensive analysis of δ13C in organic carbon, acetate, CO2, and CH4 and by determination of the isotopic enrichment factor for conversion of CO2 to CH4. This value (≈−78‰) indicates that the Gibbs free energy of hydrogenotrophic methanogenesis was more negative, implying the energetic conditions in situ were more favorable, than suggested by measured H2 partial pressures. The fermentatively produced acetate‐methyl was by about 10% lighter than the δ13C of sediment organic carbon, indicating an unusual fractionation during fermentative production of acetate. Homoacetogenesis from CO2 probably played only a minor role because the intramolecular difference between the δ13C of the carboxyl and the methyl groups of acetate was only on the order of 20‰. A remarkable microbial community is able to produce methane from organic matter in the oxidized surface layer of oligotrophic lake sediments in which methane normally is not produced, so that the ecological relevance of this potential is presently unclear.
Algal—bacterial competition for phosphorus from dissolved DNA, ATP, and orthophosphate in a mesocosm experiment
Authors: Løvdal Trond , Tanaka Tsuneo , Thingstad T. Frede
Published: January 2011

We measured the turnover of phosphorus (P) from radioactive‐labeled dissolved deoxyribonucleic acid (dDNA), adenosine triphosphate (ATP), and orthophosphate, and the partitioning of P from these sources into different size fractions of algae and bacteria in nutrient‐manipulated mesocosms. There was a transition from uptake dominated by larger organisms during balanced enrichment toward uptake dominated by smaller organisms during nitrogen (N) enrichment (P starvation). Contrary to expectation, this effect was counteracted by glucose enrichment, probably because bacterial cells increased in size in a glucose‐amended mesocosm. During P starvation, estimates of biomass‐specific affinity for all substrates were consistent with uptake becoming limited by molecular diffusion transport toward the cells. Dissolved organic phosphorus (DOP) turnover times (T) fell to ~5 min for ATP and ~1.5 h for dDNA (compared to 1.1 and 15.6 h, respectively, during balanced enrichment), coincided with little inorganic P liberated from DOP in the water, and reflected a tight coupling between hydrolysis and uptake in this situation. At one time during the experiment, the ability of algae and bacteria to compete for P was also assessed by the combination of isotope dilution experiments and affinity estimates. High affinity and low values of the term K + Sn (the half saturation constant + the natural concentration of bioavailable substrate) when the 1‐0.2‐µm size fraction was compared to the >1‐µm size fraction for all substrates indicated bacterial supremacy while in competition for both inorganic and organic P. No significant shift in algal‐bacterial competition for DOP relative to dissolved inorganic phosphorus (DIP) was found.
Strong purifying selection in the silicon transporters of marine and freshwater diatoms
Authors: Alverson Andrew J.
Published: January 2011

Marine and freshwater diatoms show several important differences in silicon physiology. In addition to containing an order of magnitude more silica in their cell walls, freshwater diatoms also appear to have a less efficient silicic acid uptake mechanism. A novel set of silicon transporters (SITs), encoded by a small gene family, import silicic acid from the environment into the diatom cell. Some evidence suggests that the disparity in uptake efficiency between marine and freshwater diatoms might be attributable to different demands on SITs in the two environments. To test this hypothesis, partial SIT genes were cloned and sequenced from 45 species of Thalassiosirales, a diatom lineage with high diversity in marine and freshwaters. Phylogenetically based codon substitution models were used to test whether SITs from marine and freshwater taxa were under similar selective constraints and whether codons in different structural locations of the protein were under similar functional constraints. Purifying selection is the predominant evolutionary force acting on SITs, irrespective of location in the protein, and differences in efficiency of silicic acid uptake between marine and freshwater diatoms are not due to sequence differences in SITs.
Acclimation to a dynamic irradiance regime changes excessive irradiance sensitivity of Emiliania huxleyi and Thalassiosira weissflogii
Authors: van de Poll Willem H. , Visser Ronald J. W. , Buma Anita G. J.
Published: January 2011

Effects of fluctuating irradiance regimes on excessive photosynthetically active radiation (PAR) and ultraviolet (UV) radiation sensitivity were assessed for Emiliania huxleyi (Lohman) and Thalassiosira weissflogii (Grunow) Fryxell and Hasle. Cultures acclimated to low irradiance were subjected to two irradiance regimes of equal daily dose: dynamic irradiance simulating vertical mixing within the water column and constant irradiance. For each regime two irradiance levels were studied. Growth was monitored for 3 d, after which pigment composition was determined. Next, excessive PAR and UV sensitivity was measured by studying viability loss during 4‐h exposure to simulated surface irradiance (SSI). Furthermore, the effects of inhibition of D1 reaction center protein turnover were investigated by incubating samples with lincomycin prior to exposure. Dynamic irradiance reduced growth rates of both species as compared to constant irradiance. Pools of light‐harvesting pigments increased in dynamic irradiance, whereas the protective pigment pools decreased compared to constant irradiance. Excessive irradiance sensitivity was enhanced in cells grown in fluctuating irradiance. Furthermore, viability loss was most pronounced in UV treatments combined with lincomycin. E. huxleyi was more sensitive to excessive irradiance than T. weissflogii, which coincided with a lower ratio between protective and light‐harvesting pigments in the former species. Irradiance modulation by deep vertical mixing influences growth, pigment composition, and excessive PAR and UV sensitivity within days.
The oxygen‐18 isotope approach for measuring aquatic metabolism in high productivity waters
Authors: Tobias Craig R. , Böhlke John Karl , Harvey Judson W.
Published: January 2011

We examined the utility of δ18O2 measurements in estimating gross primary production (P), community respiration (R), and net metabolism (P : R) through diel cycles in a productive agricultural stream located in the midwestern U.S.A. Large diel swings in O2 (±200 µmol L−1) were accompanied by large diel variation in δ18O2 (±10‰). Simultaneous gas transfer measurements and laboratory‐derived isotopic fractionation factors for O2 during respiration (αr) were used in conjunction with the diel monitoring of O2 and δ18O2 to calculate P, R, and P :R using three independent isotope‐based methods. These estimates were compared to each other and against the traditional “open‐channel diel O2‐change” technique that lacked δ18O2. A principal advantage of the δ18O2 measurements was quantification of diel variation in R, which increased by up to 30% during the day, and the diel pattern in R was variable and not necessarily predictable from assumed temperature effects on R. The P, R, and P :R estimates calculated using the isotope‐based approaches showed high sensitivity to the assumed system fractionation factor (αr). The optimum modeled ar values (0.986‐0.989) were roughly consistent with the laboratory‐derived values, but larger (i.e., less fractionation) than αr values typically reported for enzyme‐limited respiration in open water environments. Because of large diel variation in O2, P :R could not be estimated by directly applying the typical steady‐state solution to the O2 and 18O‐O2 mass balance equations in the absence of gas transfer data. Instead, our results indicate that a modified steady‐state solution (the daily mean value approach) could be used with time‐averaged O2 and δ18O2 measurements to calculate P :R independent of gas transfer. This approach was applicable under specifically defined, net heterotrophic conditions. The diel cycle of increasing daytime R and decreasing nighttime R was only partially explained by temperature variation, but could be consistent with the diel production/consumption of labile dissolved organic carbon from photosynthesis.
Changes in microcystin production in cyanobacteria exposed to zooplankton at different population densities and infochemical concentrations
Authors: Jang Min-Ho , Jung Jong-Mun , Takamura Noriko
Published: January 2011

We investigated microcystin (MC) production by four cyanobacterial strains (three Microcystis aeruginosa and one Planktothrix agardhii) in response to different grazer densities (direct exposure: zero, two, four, or eight individuals per 300 mL) and infochemical concentrations (indirect exposure: 0%, 10%, 25%, and 50%) of Daphnia magna and Moina macrocopa. MC production increased after direct exposure to both zooplankton species and was higher with increasing concentration of infochemicals. This MC production was significantly different among the control and three zooplankton treatment levels. Upon direct and indirect exposure of cyanobacteria to zooplankton, intracellular MC peaked on days 3 and 4. In most cyanobacterial strains, the peak MC contents were significantly higher in direct treatment with the highest zooplankton density and in indirect treatment with the highest concentration of zooplankton culture media filtrate than with treatments with the lowest density and concentration, respectively. Extracellular MC concentrations were much lower than intracellular ones, but both showed similar temporal patterns over the course of the experiment. Cyanobacteria directly exposed to Daphnia released greater amounts of extracellular MC than did those exposed to Moina. This is the first study to provide evidence of an induced defense of increased MC production by cyanobacteria in response to increasing zooplankton grazer density and increased concentrations of infochemicals released by zooplankton. In addition to the induction of tolerance in Daphnia to toxic Microcystis, we discuss how these reciprocal defenses may explain the coexistence of zooplankton and toxic cyanobacteria in eutrophic freshwaters.
A direct test of cyanobacterial chemical defense: Variable effects of microcystin‐treated food on two Daphnia pulicaria clones
Authors: Wilson Alan E. , Hay Mark E.
Published: January 2011

To determine the direct effects of microcystin on the fitness of herbivorous zooplankton, we experimentally added microcystin‐LR to freeze‐dried cells of palatable Chlorella and fed these compound‐treated cells to two clones of Daphnia pulicaria that had shown differing responses to a diet containing a strain of Microcystis aeruginosa that produces microcystin. The Daphnia that performed better on a diet containing live Microcystis showed reduced population growth when exposed to microcystin‐LR‐treated Chlorella, whereas the Daphnia that performed poorly on the diet containing live Microcystis was not affected by the experimental diet containing microcystin‐LR. This is the first study to unambiguously show that some Daphnia strains are and some strains are not harmed by the consumption of microcystin‐LR. These surprising results were not generated by interference from lipophilic secondary metabolites in Microcystis. When the crude lipophilic extract of Microcystis was added to dried Chlorella cells, it enhanced the fitness of both Daphnia clones. We hypothesize that the Daphnia clone more tolerant to live cells may upregulate resistance when cued by the presence of the live Microcystis cells, but not by microcystin‐LR alone. Alternatively, the Daphnia clone that grew well on a diet containing live Microcystis may sequester compounds from Microcystis that defend the cyanobacteria from autotoxicity; these compounds would have been unavailable to Daphnia consuming freeze‐dried Chlorella treated with microcystin‐LR alone. Thus, microcystin‐LR can suppress Daphnia fitness when consumed; however, the effects of microcystin vary across clones of herbivorous zooplankton and the consequences of this variance should not be overlooked when considering zooplankton‐cyanobacteria interactions.
Microzooplankton grazing in the coastal Gulf of Alaska: Variations in top‐down control of phytoplankton
Authors: Strom Suzanne L. , Macri Erin L. , Olson M. Brady
Published: January 2011

Microzooplankton grazing rates on three phytoplankton size fractions (<5, 5‐20, and >20 µm) were measured during spring and summer 2001 in the northern coastal Gulf of Alaska (CGOA). To a first approximation, microzooplankton consumed all production by phytoplankton <20 µm in size and nearly half the production by phytoplankton >20 µm, mainly diatoms. Microzooplankton (ciliate plus heterotrophic dinoflagellate) biomass ranged from 9.6 µg C L−1 to 82.2 µg C L−1. The highest levels were associated with diatom blooms and equaled those previously reported for highly productive coastal upwelling regions. Regulation of microzooplankton grazing differed according to size class. Grazing on phytoplankton <5 µm in size averaged 0.48 d−1 and was closely correlated with phytoplankton growth rates in the same size class. In contrast, grazing on phytoplankton >20 µm averaged 0.17 d−1 and was unrelated to phytoplankton growth rate in this size class. Variations in grazing pressure on these largest phytoplankton arose mainly through variations in the biomass of the larger (>40 µm) ciliates and dinoflagellates. This biomass, in turn, became more closely correlated with >20 µm chlorophyll as the season progressed, indicating removal of top‐down control on these ciliates and dinoflagellates as Neocalanus spp. copepods left the upper water column. Because microzooplankton directly consume much of the phytoplankton production in the CGOA, processes that regulate this trophic linkage have major implications for food web structure and secondary production in this coastal ecosystem.
The relative importance of microbial and classical food webs in a highly productive coastal upwelling area
Authors: Vargas Cristian A. , Martínez Rodrigo A. , Cuevas L. Antonio , Pavez Marcelo A. , Cartes Carolina , GonzÁlez Humberto E. , Escribano RubÉn , Daneri Giovanni
Published: January 2011

We present an analysis of seasonal variations in the trophic pathways of carbon in a highly productive coastal upwelling region in the Humboldt current system off Chile. Seasonal changes in phytoplankton, protozooplankton, and bacteria biomass, along with rates of primary production (PP), bacterial growth, secondary production, vertical particle fluxes, and feeding by protozooplankton, omnivorous mesozooplankton, and carnivorous gelatinous zooplankton were determined from July 2004 to June 2005. Phytoplankton biomass and PP were maximal during spring/summer months, associated with upwelling episodes. Heterotrophic nanoflagellates (HNF) were the principal consumers of bacteria, removing >100% of their biomass daily. During autumn/winter, the protozooplankton grazed down a large fraction of HNF production (56% to 96% d−1). The mesozooplankton consumed 1–6% of the PP d−1; the different size fractions of copepods were omnivorous mostly during autumn/winter months, and ctenophores preyed most strongly on small copepods (0.5% to 5% d−1). A large part of the PP was channeled through the microbial food web, and only a small part directly to copepods via the herbivore food chain. The microbial food web transfers bacterial or small algal carbon to protozooplankton, and then to mesozooplankton, and a large percentage of this carbon is also available for the gelatinous predators. Because zooplankton are not able to feed on dissolved organic matter and cyanobacteria, the combined feeding activity of zooplankton either by direct (phytoplankton) or indirect (microbial) pathways increases the yield of PP reaching the zooplankton and, eventually, the upper trophic levels. Our findings suggest that the carrying capacity for larger omnivorous and carnivorous metazoans, and even for commercially exploitable pelagic fishes, might be considerably larger than that expected from a simple herbivore‐dominated food chain in coastal upwelling areas.