bluuebunny/crossref_metadata_2025 huggingface dataset:
On the total domination subdivision numbers in graphs
Authors: Sheikholeslami Seyed
Published: May 2010

A set S of vertices of a graph G = (V, E) without isolated vertex is a total dominating set if every vertex of V(G) is adjacent to some vertex in S. The total domination number γ
t(G) is the minimum cardinality of a total dominating set of G. The total domination subdivision number sdγt
(G) is the minimum number of edges that must be subdivided (each edge in G can be subdivided at most once) in order to increase the total domination number. Karami, Khoeilar, Sheikholeslami and Khodkar, (Graphs and Combinatorics, 2009, 25, 727–733) proved that for any connected graph G of order n ≥ 3, sdγ
t(G) ≤ 2γ
t(G) − 1 and posed the following problem: Characterize the graphs that achieve the aforementioned upper bound. In this paper we first prove that sdγ
t(G) ≤ 2α′(G) for every connected graph G of order n ≥ 3 and δ(G) ≥ 2 where α′(G) is the maximum number of edges in a matching in G and then we characterize all connected graphs G with sdγ
t(G)=2γt(G)−1.
An accurate approximation of zeta-generalized-Euler-constant functions
Authors: Lampret Vito
Published: May 2010

Zeta-generalized-Euler-constant functions, $$
\gamma \left( s \right): = \sum\limits_{k = 1}^\infty {\left( {\frac{1}
{{k^s }} - \int_k^{k + 1} {\frac{{dx}}
{{x^s }}} } \right)}
$$ and $$
\tilde \gamma \left( s \right): = \sum\limits_{k = 1}^\infty {\left( { - 1} \right)^{k + 1} \left( {\frac{1}
{{k^s }} - \int_k^{k + 1} {\frac{{dx}}
{{x^s }}} } \right)}
$$ defined on the closed interval [0, ∞), where γ(1) is the Euler-Mascheroni constant and $$
\tilde \gamma
$$(1) = ln $$
\frac{4}
{\pi }
$$, are studied and estimated with high accuracy.
Otto Friedrich Bollnow’s concept of human space. A Critical Discussion on the Fundamentals of the Concepts of Space
Authors: De Silva Wasana
Published: May 2010

The concepts of space and place are well recognized and accepted in recent architectural theories and practices but definitions vary according to different interpretations. The concepts of "space and place" fall within the realms of philosophy the earliest of which can be traced to those of Aristotle whose notion of space was comprised of earthly as well as cosmic dimensions and was not an undefined Cartesian concept. Much Later, Christian Norberg Schulz has proposed the concept of ‘existential space' which was based on Jean Piaget's studies of a child's concept of space, (ontogenetical aspects of space conception 1963 -1973) ‘its socio/cultural aspects, (philogenetic problem of space conception) and philosophical phenomenological studies of his time. But his studies were inspired by many previous studies like well-known historian of religion Mircea Eliade, the art historian Dagobert Frey (1949) and the philosophical phenomenologist Otto Friedrich Bollnow. The concept of "Human Space" by O.F. Bollnow can be taken into broader discussions than the Schulz' concept of ‘existential space', because, Norberg Schulz (1971) directly related concept of ‘existential space' into more concrete ‘architectural space' of which definitions were unclear. Therefore in the realm of Architectural research on concepts of "space and place', O. F. Bollnow's ideas of ‘Man and Space' provides a fundamental basis for further critical and inspirational thinking. The intention of this paper is to reveal the idea of concept of space in Bollnow's work for further architectural research. DOI: 10.4038/besl.v7i2.1942 Built-Environment Sri Lanka Vol.7(2) 40-42
Lipopolysaccharide-Mediated Mast Cell Activation Induces IFN-γ Secretion by NK Cells
Authors: Vosskuhl Katja , Greten Tim F. , Manns Michael P. , Korangy Firouzeh , Wedemeyer Jochen
Published: May 2010

Mast cells (MCs) that are well known for their important effector function in IgE-associated immune responses play a key role in innate immune defenses. In this study, we investigate the interaction between MCs and NK cells in vitro and in vivo. We show that mouse bone marrow-derived cultured MCs activated with LPS, polyinosinic-polycytidylic acid, or CpG can stimulate NK cells to secrete increasing concentrations of IFN-γ. MCs induce a 20-fold increase in IFN-γ release from NK cells after LPS stimulation. This enhancement of IFN-γ secretion is cell contact dependent and TNF-α independent. Furthermore, we show that this interaction is in part mediated by OX40 ligand on MCs. NK cell-mediated cytotoxicity was not affected by the presence of MCs. Intracellular IFN-γ levels in splenic NK cells are significantly decreased after i.p. injection of LPS in mast cell-deficient (C57BL/6 Kitwsh/wsh) mice in comparison with wild-type mice. In conclusion, our data show for the first time a direct mast cell-dependent NK cell activation. This interaction might play an important role in innate immune defense, as it is dependent on the presence of stimulators relevant in innate immune responses.
Protein Tyrosine Nitration of Aldolase in Mast Cells: A Plausible Pathway in Nitric Oxide-Mediated Regulation of Mast Cell Function
Authors: Sekar Yokananth , Moon Tae Chul , Slupsky Carolyn M. , Befus A. Dean
Published: May 2010

NO is a short-lived free radical that plays a critical role in the regulation of cellular signaling. Mast cell (MC)-derived NO and exogenous NO regulate MC activities, including the inhibition of MC degranulation. At a molecular level, NO acts to modify protein structure and function through several mechanisms, including protein tyrosine nitration. To begin to elucidate the molecular mechanisms underlying the effects of NO in MCs, we investigated protein tyrosine nitration in human MC lines HMC-1 and LAD2 treated with the NO donor S-nitrosoglutathione. Using two-dimensional gel Western blot analysis with an anti-nitrotyrosine Ab, together with mass spectrometry, we identified aldolase A, an enzyme of the glycolytic pathway, as a target for tyrosine nitration in MCs. The nitration of aldolase A was associated with a reduction in the maximum velocity of aldolase in HMC-1 and LAD2. Nuclear magnetic resonance analysis showed that despite these changes in the activity of a critical enzyme in glycolysis, there was no significant change in total cellular ATP content, although the AMP/ATP ratio was altered. Elevated levels of lactate and pyruvate suggested that S-nitrosoglutathione treatment enhanced glycolysis. Reduced aldolase activity was associated with increased intracellular levels of its substrate, fructose 1,6-bisphosphate. Interestingly, fructose 1,6-bisphosphate inhibited IgE-mediated MC degranulation in LAD2 cells. Thus, for the first time we report evidence of protein tyrosine nitration in human MC lines and identify aldolase A as a prominent target. This posttranslational nitration of aldolase A may be an important pathway that regulates MC phenotype and function.
A Common Polymorphism in the Caspase Recruitment Domain of RIG-I Modifies the Innate Immune Response of Human Dendritic Cells
Authors: Hu Jianzhong , Nistal-Villán Estanislao , Voho Anu , Ganee Arnold , Kumar Madhu , Ding Yaomei , García-Sastre Adolfo , Wetmur James G.
Published: May 2010

Infection of human dendritic cells (DCs) by negative-strand RNA viruses, such as Newcastle disease virus, leads to the induction of the IFNβ gene, IFNB1, through the activation of the RNA helicase RIG-I, which is encoded by DDX58. Expression levels of IFNB1 and DDX58 in infected DCs showed positive correlations at the population and the single-cell levels. DDX58 has a common and potentially functional single nucleotide polymorphism, rs10813831 (A/G), encoding an Arg7Cys amino acid change in the RIG-I protein caspase recruitment domain (CARD). Quantitative RT-PCR analysis on Newcastle disease virus-infected primary DCs from 130 individuals revealed a significant association of the Arg7Cys single nucleotide polymorphism with increased IFNB1 and DDX58 transcription. Allelic imbalance analysis ruled out allele-specific DDX58 message levels and suggested that the observed association between Arg7Cys and IFNB1 and DDX58 transcription originated from a functional change in RIG-I due to the amino acid substitution in the CARD. DDX58 transfection experiments in 293T cells confirmed a biological functional difference between RIG-I 7Cys and the more common RIG-I 7Arg. Taken together, these data indicate that the innate immune response to viral infection of human cells is modified by a functional polymorphism in the RIG-I CARD.
α-Synuclein Activates Microglia by Inducing the Expressions of Matrix Metalloproteinases and the Subsequent Activation of Protease-Activated Receptor-1
Authors: Lee Eun-Jung , Woo Moon-Sook , Moon Pyong-Gon , Baek Moon-Chang , Choi In-Young , Kim Won-Ki , Junn Eunsung , Kim Hee-Sun
Published: May 2010

The mutation or overexpression of α-synuclein protein plays a pivotal role in the pathogenesis of Parkinson’s disease. In our preliminary experiments, we found that α-synuclein induced the expression of matrix metalloproteinases (MMPs) (MMP-1, -3, -8, and -9) in rat primary cultured microglia. Thus, the current study was undertaken to determine the roles of MMPs in α-synuclein–induced microglial activation. The inhibition of MMP-3, -8, or -9 significantly reduced NO and reactive oxygen species levels and suppressed the expression of TNF-α and IL-1β. Notably, MMP-8 inhibitor suppressed TNF-α production more efficaciously than MMP-3 or MMP-9 inhibitors. Inhibition of MMP-3 or -9 also suppressed the activities of MAPK, NF-κB, and AP-1. Previously, protease-activated receptor-1 (PAR-1) has been associated with the actions of MMPs, and thus, we further investigated the role of PAR-1 in α-synuclein–induced inflammatory reactions. A PAR-1–specific inhibitor and a PAR-1 antagonist significantly suppressed cytokine levels, and NO and reactive oxygen species production in α-synuclein–treated microglia. Subsequent PAR-1 cleavage assay revealed that MMP-3, -8, and -9, but not α-synuclein, cleaved the synthetic peptide containing conventional PAR-1 cleavage sites. These results suggest that MMPs secreted by α-synuclein–stimulated microglia activate PAR-1 and amplify microglial inflammatory signals in an autocrine or paracrine manner. Furthermore, our findings suggest that modulation of the activities of MMPs and/or PAR-1 may provide a new therapeutic strategy for Parkinson’s disease.
Generation of Th1-Polarizing Dendritic Cells Using the TLR7/8 Agonist CL075
Authors: Spranger Stefani , Javorovic Miran , Bürdek Maja , Wilde Susanne , Mosetter Barbara , Tippmer Stefanie , Bigalke Iris , Geiger Christiane , Schendel Dolores J. , Frankenberger Bernhard
Published: May 2010

In this paper, we describe a new method for preparation of human dendritic cells (DCs) that secrete bioactive IL-12(p70) using synthetic immunostimulatory compounds as TLR7/8 agonists. Monocyte-derived DCs were generated using a procedure that provided mature cells within 3 d. Several maturation mixtures that contained various cytokines, IFN-γ, different TLR agonists, and PGE2 were compared for impact on cell recovery, phenotype, cytokine secretion, migration, and lymphocyte activation. Mixtures that included the TLR7/8 agonists R848 or CL075, combined with the TLR3 agonist polyinosinic:polycytidylic acid, yielded 3-d mature DCs that secreted high levels of IL-12(p70), showed strong chemotaxis to CCR7 ligands, and had a positive costimulatory potential. They also had excellent capacity to activate NK cells, effectively polarized CD4+ and CD8+ T cells to secrete IFN-γ and to induce T cell-mediated cytotoxic function. Thereby, mature DCs prepared within 3 d using such maturation mixtures displayed optimal functions required for vaccine development.
NKG2D Costimulates Human Vγ9Vδ2 T Cell Antitumor Cytotoxicity through Protein Kinase Cθ-Dependent Modulation of Early TCR-Induced Calcium and Transduction Signals
Authors: Nedellec Steven , Sabourin Caroline , Bonneville Marc , Scotet Emmanuel
Published: May 2010

Human Vγ9Vδ2 T cells, a major innate-like peripheral T cell subset, are thought to play in vivo an important role in innate and adaptive immune responses to infection agents and tumors. However, the mechanisms regulating their broad effector functions, such as cytotoxicity and cytokine responses, remain poorly understood. In this study, we used single-cell calcium video imaging to analyze the early intracellular events associated with TCR-induced Vγ9Vδ2 T cell functional responses. When compared with other human T cell subsets, including NKT and Vδ2neg γδ T cells, TCR/CD3-activated Vγ9Vδ2 T cells displayed an unusually delayed and sustained intracellular calcium mobilization, which was dramatically quickened and shortened on costimulation by NKG2D, a main activating NKR regulating γδ T cell tumor cytolysis. Importantly, the protein kinase Cθ transduction pathway was identified as a main regulator of the NKG2D-mediated costimulation of antitumor Vγ9Vδ2 cytolytic responses. Therefore, this study identifies a new mechanism regulating Vγ9Vδ2 T cell functional plasticity through fine-tuning of early signal transduction events.
Primary Coronary Embolism as an Unusual Manifestation of Nonbacterial Thrombotic Endocarditis in a Patient with Gastric Cancer
Authors: Ferlan Giovanni , Fiorella Annalisa , De Pasquale Claudio , Tunzi Francesco
Published: May 2010

Nonbacterial thrombotic endocarditis (NBTE) is a rare clinical condition characterized by the presence of sterile vegetations on valvular leaflets Gross and Friedberg (1936). The most frequent cause of NBTE is antiphospholipid syndrome Hughson and et al. (1993); malignancy, through an intrinsic condition of hypercoagulability, is the second most common cause Thomas (2001). Systemic thromboembolic complications are frequently associated with this condition, but coronary embolism is not common. We report the case of a patient with NBTE secondary to gastric adenocarcinoma with clinical symptoms of coronary and systemic emboli.
Lead Nephropathy: Revisiting an Overlooked Cause of Kidney Disease
Authors: Alasia Datonye Dennis
Published: May 2010

Despite the recognition of lead nephropathy as a consequence of environmental and occupational lead exposure, lead nephropathy still appears to be underrecognized by physicians as a cause and promoter of chronic kidney disease (CKD), especially in people with more apparent causative factors such as diabetes and hypertension. This review focuses on the clinical, pathophysiological and epidemiological perspectives of lead nephropathy with the objective of promoting the awareness of this important but overlooked cause of CKD among physicians. Literature was reviewed using available medical journals and online literature search through Google, Pubmed, Medline, Medscape and HINARI databases. The key words employed were: Lead Nephropathy, Environmental and Occupational lead exposure and chronic kidney disease. Lead nephropathy which is a tubulointerstitial nephritis, may present acutely or chronically in association with hypertension. The clinical diagnosis of lead nephropathy is complex, because the symptoms are varied and non-specific especially with subclinical nephrotoxicity. The recognition of lead nephropathy can be enhanced if physicians have a high index of suspicion in the assessment of patients with renal disease. It is recommended that the evaluation of environmental and occupational nephrotoxins like lead be incorporated into programs for the prevention of CKD, especially in developing countries where lead exposure and toxicity still remain largely unchecked and the prevalence and burden of CKD is increasing.
A Seventeen-Year-Old Female with Hepatosplenic T-cell Lymphoma Associated with Parvoviral Infection
Authors: Haque Saadiya A. , Xiang Ying , Ozdemirli Metin , Shad Aziza , Kallakury Bhaskar
Published: May 2010

Hepatosplenic T-cell lymphoma (HSTL) is rare, being derived from cytotoxic T-cells, and manifests as an extranodal systemic lymphoma. We present an unusual case of a seventeen-year-old female, with no significant prior medical history, presenting with a hepato­splenic T-cell lymphoma. The diagnosis was confirmed by histological examination, immunohistochemisty, and flow cytometry. A staging work-up demonstrated bone marrow involvement by HSTL with concomitant intranuclear parvoviral inclusions.
Primary hepatocellular carcinoma in ectopic liver masquerading as left adrenal carcinoma: a rare occurrence
Authors: Singh Vishwajeet , Sinha Rahul Janak , Sankhwar Satya Narayan , Kumar Shailendra , Mehrotra Bandana , Puri Mohini , Sengottayan Vengetesh Kilvani
Published: May 2010

We report a unique case of primary hepatocellular carcinoma in an ectopic liver rest in the left renal hilum masquerading as a left adrenal tumor. Adrenal tumors have been reported within adrenal rests inside the liver but hepatocellular carcinoma in ectopic liver rests in the adrenal area is an extremely rare entity. To the best of our knowledge, this is the first case report from the Indian subcontinent to describe this event in the English literature.

Our patient, a sixty-year-old, non-diabetic, non-hypertensive male, presented with a history of left flank pain for the past six months. He was a chronic smoker and also consumed excessive amounts of alcohol. He had chronic obstructive pulmonary disease and was hepatitis B surface antigen positive. A contrast enhanced computer tomography scan of the abdomen showed an 8×8×8 cm, well-defined, heterogeneously enhancing mass with central necrosis, in the left suprarenal region. The provisional diagnosis of an adrenal tumor was made and open transperitoneal excision of the tumor along with two enlarged lymph nodes was done. Immunohistochemistry staining of the specimen revealed it to be a primary hepato cellular carcinoma. The patient died within six months of surgery owing to extensive metastases. We concluded that chronic hepatitis B infection and chronic and excessive alcohol consumption and/or chronic smoking may have been the predisposing factors for the occurrence of primary hepatocellular carcinoma in the liver rest in our patient. The prognosis appears to be poor despite surgical management.
Gliosarcoma: a study of four cases
Authors: Güney Yildiz , Hiçsönmez Ayse , Yilmaz Sercan , Adas Yasemin Güzle , Andrieu Meltem Nalca
Published: May 2010

Gliosarcomas (GS) are highly malignant and rare tumors of the central nervous system with a poor prognosis. We report here on four patients with GS, the median survival for whom was 9.25 months. Prognosis of GS remains poor, and a multidisciplinary approach (surgery, radiation therapy, and chemotherapy) seems to be associated with slightly more prolonged survival times.
The relationship between organisational climate and employee satisfaction in a South African information and technology organisation
Authors: Castro Monia L. , Martins Nico
Published: May 2010

Orientation: Organisational climate and job satisfaction are distinct but related constructs, and both appear to influence employees’ understanding of the work environment and their level of job satisfaction.Research purpose: The objective of this study was to explore the relationship between organisational climate and job satisfaction to determine whether employees’ perceptions of the work environment influence their level of job satisfaction.Motivation for the study: Organisations are facing more challenges than ever before. These challenges are not unique to any specific organisation or industry, but affect all organisations.Organisational climate in particular is constantly challenged by changes impacting organisations today.Research design, approach and method: An organisational climate questionnaire was administered to a convenience sample of 696 employees from a population of 1453 employees working in three regions in which the organisation was operational. Confirmatory and exploratory factor analyses were used to investigate the structure of the climate model.Main findings: The revised 12-factor model (after the confirmatory factor analysis) fitted the data best and the researchers therefore decided to proceed with the revised 12-factor model (11 dimensions) for further analysis. A stepwise regression was conducted and nine dimensions of organisational climate were found to predict job satisfaction. The results indicated a strong positive correlation (r = 0.813, p< 0.01) between organisational climate and the dependent variable of job satisfaction.Practical implications: This study provided support for the view that line managers and human resource practitioners should be aware that different biographical groups have different needs that can influence their job satisfaction levels and different perceptions of the climate within the organisation and that this impacts on their behaviour.Contribution: The findings of this study indicated a positive relationship between organisational climate scores and job satisfaction scores and thus, regardless of how the dimensions are perceived, organisational climate has an influence on job satisfaction.
Dynamics of dissolved methane and methane oxidation in dimictic Lake Nojiri during winter
Authors: Utsumi Motoo , Nojiri Yukihiro , Nakamura Takeshi , Nozawa Takeshi , Otsuki Akira , Takamura Noriko , Watanabe Makoto , Seki Humitake
Published: May 2010

Changes in the vertical distribution of dissolved CH4 were monitored during the autumnal lake overturn period in mesotrophic Lake Nojiri, Japan (4.4 km2 in area and 9.4 X 107 m3 in vol). A survey in 1992 revealed that the surface CH4 concentration was highest in December, when the lake overturned. During the following two winters (1993–1994 and 1994–1995) we carried out detailed sampling during the autumnal overturn period. As a result of lake overturn in mid‐December, CH4 that had accumulated in the hypolimnion during the stratification period mixed rapidly throughout the water column. Increased CH4 in the epilimnion quickly disappeared after the overturn as a result of the rising of CH4 oxidation activity throughout the water column. The in situ‐specific CH4 oxidation rate peaked at 0.274, 0.235, and 1.01 d−1 at 0.5, 20, and 36 m, respectively, during the overturn, and then declined the following month. During this period, the diffusive flux of methane across the air‐water interface increased but was not the dominant sink (avg rate of 4.5 kg lake−1 d−1); instead, methane oxidation in the water column was the dominant CH4 sink (avg rate of 67.8 kg lake−1 d−1), removing ~94% of the CH4 during the overturn period. A significant methane flux from the bottom sediments throughout the overturn period was confirmed but decreased gradually as the overturn proceeded. The production of organic carbon as a result of CH4 oxidation in the water column by methanotrophs was comparable in extent to that generated by primary production at that time.
Influence of carbonate dissolution on survival of shell‐bearing meiobenthos in nearshore sediments
Authors: Green Mark A. , Aller Robert C. , Aller Josephine Y.
Published: May 2010

Sediment plugs containing natural populations of benthic foraminifera and juvenile bivalves were introduced into seawater chambers realistically undersaturated (experimental) and saturated (control) with respect to biogenic carbonates in order to evaluate the impact of carbonate dissolution on the survival of carbonate‐bearing meiobenthos. Experimental manipulation of saturation state clearly demonstrated that substantial calcite undersaturation, in a range typical of organic‐rich surface sediment (ωcalcite = IMP/K′sp = ~0.4), not only resulted in dissolution of abandoned tests but also increased mortality of the live benthic foraminfera Elphidium clavatum (excfavatum) threefold relative to controls. Dissolution of discarded foraminifera tests occurred on time scales of 14 d. In addition, although no statistically significant correlation of dissolution with survival was found for the aragonitic bivalves Nucula annufata and Tellina agilis, experiments did show a tendency for increased mortality in undersaturated sediments. Mortality induced by calcite and aragonite undersaturation has implications for existing theories on production recruitment of shell‐bearing benthos in near‐shore environments and the coupling of biogeochemical processes with the benthic community. These results help explain the seasonal dynamics of foraminifera reported previously in the literature and show that both live and dead assemblages of some organisms are components of the annual cycle of CaCO3 dissolution and precipitation in near‐shore, organic‐rich sediments.
Theoretical developments on the optical properties of highly turbid waters and sea ice
Authors: MaBone Robert A.
Published: May 2010

The photon diffusion equation is derived in a direct manner from the radiative transfer equation and is shown to be an asymptotic equation that can be directly related to asymptotic radiative transfer theory. Diffusion theory predicts that the asymptotic diffuse attenuation coefficient, K∞, is related to the beam attenuation coefficient, c, the single scattering albedo, ω0, and the asymmetry parameter, g, of the scattering phase function by . Kirk has previously published a K relationship based entirely on Monte Carlo radiative transfer simulations that can be expressed in the form , where G is a regression parameter. Equating these two results gives G = 3(1 − g) + 2(1/ω0 − 1), showing explicitly, as Kirk found numerically, how G is a function of w0 and g. These results are expected to be valid for highly turbid water where ω0 > 0.95. Comparison of the analytical expression for G with Kirk's regression value, using ω0 of 0.99, differed by only 2%.
Burial efficiency of phosphorus and the geochemistry of iron in continental margin sediments
Authors: Anschutz Pierre , Zhong Shaojun , Sundby Bjørn , Mucci Alfonso , Gobeil Charles
Published: May 2010

We have examined the distributions of phosphorus and iron in sediments from well‐oxygenated environments on the Atlantic Canadian and the Portuguese continental margins and from the anoxic region of the Chesapeake Bay. The measurements include total, citrate‐dithionite‐bicarbonate (CDB) extractable, ascorbate extractable, and dissolved P and Fe; acid volatile sulfide; and pyrite. A surface layer (varying in thickness between 2 and 4 cm) enriched in P and Fe was revealed by both the CDB and the ascorbate extractions in all sediments except those from the Chesapeake Bay. The amount of phosphate extracted by the two reagents was similar, but more iron was extracted by the CDB reagent, probably because of its ability to dissolve crystalline iron oxides. Within the Fe and P‐enriched surface layer, the Fe : P ratio in the ascorbate extract varied within a narrow range (6–14), as did the soluble‐reactive phosphate (SRP) concentration (5–16 µM), suggesting that SRP is in sorption equilibrium with the solid phase. Our data are consistent with a dynamic cycling of P and strong interactions between the cycles of P, Fe, and sulfur in many marine environments. The reductive dissolution of amorphous Fe during burial and the formation of pyrite diminish the capacity of the sediment to sequester P, and only a portion of the P that arrives at the sediment–water interface actually gets buried with the sediment.
The effect of carbohydrate production by the diatom Nitzschia curvilineata on the erodibility of sediment
Authors: Sutherland T. F. , Grant J. , Amos C. L.
Published: May 2010

The effect of growth and carbohydrate production by the diatom Nitzschia cuwilineata on sediment erodibility was explored in laboratory flume experiments. Diatom cultures, incubated on sediment, were monitored daily for chlorophyll and carbohydrate concentrations and eroded in a recirculating flume at successive stages of growth. Because variations in erosion rate were far greater than variations in erosion threshold during the diatom growth period, erosion rate may be a more sensitive index of sediment stability. Erosion rate was negatively correlated with sediment chlorophyll (r2 = 0.759; P = 0.024) and bulk carbohydrate (r2 = 0.958; P = 0.001) concentrations. A strong negative correlation was found between the sediment bulk carbohydrate‐to‐chlorophyll ratio and erosion rate (r2 = 0.996; P < 0.00l), suggesting that this ratio would serve as a good indicator of sediment erodibility. The size of eroding particles or aggregates increased with the age of the biofilm, probably due to the pervasion of sediment with mucilage and changes in “stickiness” of the resulting sediment microfabric. Sediment stability increased throughout the stationary phase of growth regardless of lift forces produced by trapped bubbles within the biofilm and progressively smaller increases in sediment carbohydrate concentrations during this period. Knowledge of the physiological status of diatom biofilms is essential for the quantitative prediction of sediment transport, since diatom growth phase alters the behavior of sediment erosion.
Temperate viruses and lysogeny in Lake Superior bacterioplankton
Authors: Tapper Mark A. , Hicks Randall E.
Published: May 2010

The morphology and abundance of free viruses were measured in spring, summer, and fall at one site in Lake Superior. Free viral head sizes ranged from 10 to 70 nm and tail length ranged from 10 to 110 nm. The vast majority (98%) of free viral head sizes were ≤60 nm, smaller than reported in most freshwater habitats. Most of these free viruses (70%) had polyhedral heads and tails, indicative of bacteriophage. Free viral abundance only ranged from 0.1 to 9 × l06 viruses ml−1 in the surface microlayer (top 20 µm) and subsurface water (20 m) in Lake Superior, but viruses were 2–15 times more abundant in the surface microlayer. This difference may be due to the enrichment of bacterial hosts, higher levels of UV light that induce temperate phage, or differences in viral burst sizes in the surface microlayer relative to subsurface water. Bacterioplankton were always more abundant than free viruses in both the surface microlayer and subsurface water, which resulted in some of the lowest virus‐tobacterium ratios reported for marine or freshwater environments. Temperate viruses from both habitats responded equally to mitomycin‐C and UV light treatments used to induce prophage into lytic cycles. An estimated O.l–7.4% of the bacterioplankton from this site in Lake Superior contained temperate prophage depending on viral burst sizes that were assumed. Three times more bacteria in the surface microlayer may contain temperate viruses compared to bacterioplankton in subsurface waters. In the western arm of Lake Superior, bacterioplankton infected by temperate phage may be more important for the survival of bacteriophage populations than as future carbon sources for new microbial production.
Bloom dynamics and sedimentation of Peridinium gatunense in Lake Kinneret
Authors: Zohary Tamar , Pollingher Utsa , Hadas Ora , Hambright David
Published: May 2010

Temporal changes in the abundance of Peridinium gatunense Nygaard in the water column of warm monomictic Lake Kinneret were followed during 1990–1994. Sedimentation rates of this dinoflagellate were followed concurrently by means of sediment traps with and without a preservative (Formalin), positioned at the base of the epilimnion and within the hypolimnion, for exposure periods of 2–3 weeks. Upper trap catches of total P. gatunense (live cells + dead cells + thecae + protoplasts + cysts) were nearly always higher than lower trap catches, partly due to decomposition of the cells as they sank through the water column. Over the S‐year period, total P. gatunense sedimentation rates ranged over 4 orders of magnitude, from values <0.001 to 8.5 g (WW) m−2 d−1. A typical seasonal pattern was observed in which sedimentation rates were relatively low during the bloom increase phase, with thecae (from cell division) being the main component, and increased substantially after the peak of the bloom, when the relative contribution of senescent cells, dead cells and protoplasts increased substantially. Cysts were trapped in low numbers, usually 1–2 orders of magnitude fewer than live cells. Interannual variations in total P. gafunense sedimentation were large and independent of the size of bloom—the proportion of annual P. gatunense production reaching the hypolimnetic traps ranged from 6% in 1994, the year with the largest bloom, to 68% in 1991, a year with an average‐size bloom. The high value was exceptional and we speculated that it resulted from higher resuspension and more severe nutrient limitation of microbial decomposition during that low water level, drought year. On average, thecae accounted for 75% of total P. gafunense sedimentation despite being only 55% of the P. gatunense‐produced biomass, suggesting that thecae were more refractory or less grazed than protoplasts. Thecal C:N:P ratio of <3,000:19:1 (vs. 276:51:1 for protoplasts) indicated that microbial decomposition of thecae is likely to require N and P inputs from other sources. Ultimately, our study highlights for the first time that annual dinoflagellate sedimentation rates may vary dramatically as a result of other processes such as decomposition, resuspension, and grazing, leading to dramatic variations in the amount of organic matter reaching the bottom sediments.
Biologically induced calcite and its isotopic composition in Lake Ontario
Authors: Hodell David A. , Schelske Claire L. , Fahnenstiel Gary L. , Robbins Lisa L.
Published: May 2010

We studied water, sediment trap, and core samples from eastern Lake Ontario to reconstruct the factors controlling the biologically induced production and sedimentation of calcite during so‐called whiting events. Calcite accumulation and its isotopic composition are controlled by a complex set of interrelated factors, including temperature, primary productivity, and the abundance of pica‐cyanobacteria during the stratified period. Calcite precipitation is highly correlated to lake temperature, because physical and biological factors interact to produce conditions favorable for whitings during warm years when the lake stratifies early in the seasonal cycle. Carbonate stratigraphies in multiple cores from eastern Lake Ontario revealed similar patterns of historical variation in percent carbonate. An exponential rise in carbonate accumulation occurred in nine cores after 1930, culminating in peak values in the early 1980s. This rise was related to historic increases in primary productivity resulting from increased phosphorus loading to Lake Ontario. Superimposed upon this rise were four peaks (centered on 1940–1942, 1957–1961, 1971–1977, and 1983) that correlate with maxima in summer air‐temperature anomalies from the Great Lakes region and with strong El Niiio events. These peaks are also associated with maxima in δ13C values and minima in δ18O values of carbonate, lending support to our model that more calcite is precipitated with higher δ13C values during warm years when thermal stratitication occurs early in the seasonal cycle. Beginning in the mid‐1980s calcite accumulation and its δ13C ratio began to decrease, suggesting a reduction in primary productivity in surface waters, probably related to lower phosphate concentrations in epilimnetic waters of Lake Ontario during the stratified period. Reduced summer P loading may be explained either by a lagged response to P abatement measures that began in the late 1970s or by decreased P loading from upstream Lake Erie beginning in the late 1980s as a result of the establishment of filter‐feeding zebra mussels.
Production, sedimentation, and isotopic composition of organic matter in Lake Ontario
Authors: Hodell David A. , Schelske Claire L.
Published: May 2010

Organic matter and its carbon and nitrogen isotopic composition were measured in sequential sediment trap and core samples from the Rochester Basin of Lake Ontario to evaluate their usefulness in reconstructing historic changes in lake productivity. The greatest flux of organic matter from the epilimnion occurred during late summer and coincided with whiting events, indicating that calcite precipitation is an effective mechanism for sedimenting organic matter. Carbon isotopes of organic matter were low prior to the onset of stratification, increased to maximum values in late summer, and then decreased following fall overturn. This pattern is controlled mainly by the timing of stratification and primary productivity, which preferentially removes 12CO2 from the epilimnion. The physiological effect of decreased carbon isotopic fractionation with decreasing supplies of [CO2]aq may have also contributed to increased δ13CorgC. Nitrogen isotopes showed a seasonal pattern opposite to that of carbon, whereby δ15N values were low during the summer stratified period and high for the remainder of the year. Seasonal variability in δ15NorgN probably reflects changes in the source of sedimented organic particles, which is dominated by isotopically depleted phytodetritus during the stratified period and isotopically enriched organic matter from heterotrophic or detrital sources during the mixed period. A comparison of organic carbon accumulation rates and δ13CorgC between sediment cores collected in 1987 and 1993–1994 confirms earlier predictions that diagenetic processes reduce the mass accumulation of organic carbon in the zone of oxic pore waters, but will not change the δ13CorgC values. All cores analyzed for δ13CorgC display the reproducible pattern of a progressive increase in the 19OOs, peaking in the early to mid‐1970s, and then decreasing to the present. This pattern matches the historical trends of phosphorus loading to the basin, suggesting that δ13C of organic carbon is a reliable proxy for paleoproductivity and responds to spring phosphorus supplies in the water column. The δ15N of sedimentary organic matter increased linearly from 1840 to 1960 at a rate of 0.3ppt per decade, and remained relatively constant thereafter except for an increase in the upper few centimeters of sediment. The increase in δ15NorgN reflects a combination of factors, including early forest clearance by Europeans, increased sewering by municipalities after 1940, and increased nitrate utilization as productivity increased in the lower Great Lakes. Increased rates of denitrification in the central basin of upstream Lake Erie from the 1930s to the early 1970s may have also contributed to the rise in δ15NorgN values.
Nitrogen isotope fractionation during the uptake and assimilation of nitrate, nitrite, ammonium, and urea by a marine diatom
Authors: Waser N. A. D. , Harrison P. J. , Nielsen B. , Calvert S. E. , Turpin D. H.
Published: May 2010

Knowledge of the fractionation of nitrogen isotopes by phytoplankton is a key requirement for the calibration of the new δ15N paleotracer. An essential part of information required in this calibration concerns the magnitude of isotopic fractionation during the incorporation of N substrates by phytoplankton. To this end, the δ15N of batch cultures of Thalassiosira pseudonana grown on nitrate, nitrite, ammonium, and urea was determined. This paper reports the first δ15N study of phytoplankton growth on urea (e.g. organic N substrate). The δ15N of the particulate nitrogen (PN) collected during the logarithmic growth phase, thus for N‐sufficient cells, was lower than the δ15N of the source due to kinetic isotope fractionation. With increasing drawdown of the N substrate, the δ15N of the accumulating PN increased in accordance with the Rayleigh distillation model. Enrichment factors (ε) derived from a least‐squares analysis of the accumulated δ15NPN data were 5.2 ± 0.2‰, 0.9 ± 0.6‰, 20 ± 1‰, and 0.8 ± 0.6‰ for NO3−, NO2−, NH4+, and urea incorporation, respectively. Overall, ε values for nitrate incorporation were consistent with field estimates of ~6‰ and could be used to estimate past relative nitrate utilization as estimated from the 615N of bulk sedimentary organic matter.
The effect of buoyant biofilms on the erodibility of sublittoral sediments of a temperate microtidal estuary
Authors: Sutherland T. F. , Amos C. L. , Grant J.
Published: May 2010

An in situ benthic flume (Sea Carousel) was deployed at eight stations along a transect (Upper South Cove, Nova Scotia) to examine the influence of biofilms on sediment erodibility. Subsamples of the material eroded within the Sea Carousel were collected by pumping and were analyzed for suspended particulate matter (SPM). Undisturbed syringe cores of the seabed were also collected and analyzed for major physical properties (bulk density, mineralogy, grain size) and organic character (chlorophyll, pheopigment, colloidal carbohydrate, organic content). Strong relationships between erosion thresholds and rates and sediment chlorophyll (r2 = 0.948, r2 = 0.875) and colloidal carbohydrate (r2 = 0.854, r2 = 0.774) content were observed, suggesting that both pigment and mucilage biotilm variables serve as good indicators of sediment stability. Erosion rates varied by a factor of 7 along the station transect, while erosion thresholds varied only by a factor of 2. Thus, erosion rate was a more sensitive indicator of trends in sediment stability than was erosion threshold. X‐ray computed tomography revealed the presence of a buoyant chlorophyll‐containing gel mud in the uppermost millimeters of the sediment column. The sectioning of undisturbed syringe cores revealed that the buoyant layer was associated with the surface chlorophyll layer. The reduction of sediment weight (geostatic load) in the surface biogenic layer may have a significant effect on sediment erodibility and explain the low erosion thresholds observed in this estuary.
Partitioning particulate light absorption: A budget for a Mediterranean bay
Authors: Duarte Carlos M. , Agustí Susana , Satta Maria Paola , Vaqué Dolors
Published: May 2010

The contribution of different components of the plankton (autotrophs and heterotrophic bacteria, heterotrophic flagellates, and mixo‐ and heterotrophic ciliates) and suspended inorganic particles to light absorbed by particles in a Mediterranean bay was examined based on a 2‐year time series of particulate light absorption (400–700, 400, and 675 nm), the biomass of planktonic microorganisms, and the mass of suspended inorganic particles. The average (±SE) particulate light absorption coefficient for the photosynthetically active radiation (PAR) range (0.035 ± 0.002 m−1) was characteristic of relatively clear coastal waters but showed great variability on occasions. A substantial fraction (53–73%, depending on the wavelength examined) of this variability could be accounted for by changes in the abundance of inorganic suspended matter, as well as planktonic organisms. The specific light absorption by autotrophs was less variable over the three spectral bands considered than those of microheterotrophs and inorganic particles, which dropped sharply with increasing wavelength. Inorganic particles contributed, on the average, 48 and 74% of the total particulate absorption for the PAR waveband and at 400 nm, respectively, with their contribution to light absorption at 675 nm being negligible. Autotrophs dominated light absorption at 675 nm (on average 45.8% of total particulate absorption), whereas mixo‐ and heterotrophic ciliates and bacteria together contributed, on average, 22.5% of the total light absorption at this wavelength. The combined light absorption coefficient of microheterotrophs at 400 nm (0.0126 m−1) was similar to that of autotrophs (0.013 m−1). These results documented the dominant role that inorganic particles play in the absorption of blue light in the Bay of Blanes and showed that the particulate light absorption by autotrophs was often comparable to that of heterotrophs.
Isotope fractionation and sulfur metabolism by pure and enrichment cultures of elemental sulfur‐disproportionating bacteria
Authors: Canfield D. E. , Thamdrup B. , Fleischer S.
Published: May 2010

We have explored the sulfur metabolism and accompanying fractionation of sulfur isotopes during the disproportionation of elemental sulfur by seven different enrichments and three pure bacterial cultures. Cultures were obtained from both marine and freshwater environments. In all cases appreciable fractionation accompanied elemental sulfur disproportionation, with two ranges of fractionation observed. All cultures except Desulfobulbus propionicus produced sulfide depleted in 34S by between 5.5 and 6.9 per mil (avg of 6.3 per ml) and sulfate enriched in 34S by between 17.1 and 20.2 per mil (avg of 18.8 per ml). The narrow range of fractionations suggests a conserved biochemistry for the disproportionation of elemental sulfur by many different marine and freshwater bacteria. Fractionations accompanying elemental sulfur disproportionation by Db. propionicus were nearly twice as great as the others, suggesting a different cellular level pathway of sulfur processing by this organism. In nearly every case pyrite formation accompanied the disproportionation of elemental sulfur. By using sulfur isotopes as a tracer of sulfur source, we could identify that pyrite formed both by the addition of elemental sulfur to FeS and from reaction between FeS and H.S. Both processes were equally fast and up to 104−105 times faster than expected from the reported kinetics of inorganic pyrite‐formation reactions. We speculate that bacteria may have enhanced rates of pyrite formation in our experimental systems. The organisms explored here have different strategies for growth and survival, and they may be active in environments ranging from dissolved sulfide‐poor suboxic sediments to interfaces supporting steep opposing gradients of oxygen and sulfide. A large environmental range, combined with high bacterial numbers, significant isotope fractionations, and a possible role in pyrite formation, make elemental sulfur‐disproportionating bacteria potentially significant actors in the sedimentary cycling of sulfur compounds.
Accumulation of trace elements in a marine copepod
Authors: Wang Wen-Xiong , Fisher Nicholas S.
Published: May 2010

We measured assimilation efficiencies (AEs) from ingested algal food, uptake rates from the dissolved phase, and efflux rate constants of five trace elements (Ag, Cd, Co, Se and Zn) in the marine copepod Temora longicornis. AEs of Ag, Cd, Co, Se, and Zn from two diatom diets were 13, 35, 14, 59, and 61%, respectively. AEs of metals from ingested natural seston collected during the spring phytoplankton bloom in Long Island Sound were comparable to AEs from diatoms. The assimilation of all trace elements within the T. longicornis gut took longer (4–15 h) than the gut passage time of ingested food particles. The rate constant of metal uptake from the dissolved phase was highest for Ag, followed by Zn > Cd > Co > Se. Efflux rate constants for all trace elements ranged from 0.08 to 0.30 d−1, indicating that metals were regenerated at a very fast rate in these animals. Generally, the efflux rate of metals was higher following uptake from food than uptake from the dissolved phase. The retention half‐times of trace elements in copepod carcasses were 0.6–3.3 d. A bioenergetic‐based kinetic model was used to quantify the relative importance of metal uptake in copepods from different pathways. The model indicates that under conditions typically encountered by copepods in nature, >50% of Zn and >98% of Se in copepods are obtained from ingested food. For Ag, Cd, and Co, >50% accumulates from the dissolved phase. The relative importance of trace element uptake from the dissolved phase vs. particulate ingestion in the overall metal uptake depends greatly on the metal AE, the feeding rate of copepods, and the partition coefficient of metals in ingested food particles.