bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency of Multiple Blood Meals Taken in a Single Gonotrophic Cycle by Anopheles arabiensis Mosquitoes in Macha, Zambia
Authors: Norris Laura C. , Fornadel Christen M. , Hung Wei-Chien , Pineda Fernando J. , Norris Douglas E.
Published: July 2010

Anopheles arabiensis is a major vector of Plasmodium falciparum in southern Zambia. This study aimed to determine the rate of multiple human blood meals taken by An. arabiensis to more accurately estimate entomologic inoculation rates (EIRs). Mosquitoes were collected in four village areas over two seasons. DNA from human blood meals was extracted and amplified at four microsatellite loci. Using the three-allele method, which counts ≥ 3 alleles at any microsatellite locus as a multiple blood meal, we determined that the overall frequency of multiple blood meals was 18.9%, which was higher than rates reported for An. gambiae in Kenya and An. funestus in Tanzania. Computer simulations showed that the three-allele method underestimates the true multiple blood meal proportion by 3–5%. Although P. falciparum infection status was not shown to influence the frequency of multiple blood feeding, the high multiple feeding rate found in this study increased predicted malaria risk by increasing EIR.
Microgeographic Genetic Variation of the Malaria Vector Anopheles darlingi Root (Diptera: Culicidae) from Córdoba and Antioquia, Colombia
Authors: Gutiérrez Lina A. , Gómez Giovan F. , González John J. , Castro Martha I. , Luckhart Shirley , Conn Jan E. , Correa Margarita M.
Published: July 2010

Anopheles darlingi is an important vector of Plasmodium spp. in several malaria-endemic regions of Colombia. This study was conducted to test genetic variation of An. darlingi at a microgeographic scale (approximately 100 km) from localities in Córdoba and Antioquia states, in western Colombia, to better understand the potential contribution of population genetics to local malaria control programs. Microsatellite loci: nuclear white and cytochrome oxidase subunit I (COI) gene sequences were analyzed. The northern white gene lineage was exclusively distributed in Córdoba and Antioquia and shared COI haplotypes were highly represented in mosquitoes from both states. COI analyses showed these An. darlingi are genetically closer to Central American populations than southern South American populations. Overall microsatellites and COI analysis showed low to moderate genetic differentiation among populations in northwestern Colombia. Given the existence of high gene flow between An. darlingi populations of Córdoba and Antioquia, integrated vector control strategies could be developed in this region of Colombia.
Disinfection By-Product Formation and Mitigation Strategies in Point-of-Use Chlorination with Sodium Dichloroisocyanurate in Tanzania
Authors: Lantagne Daniele S. , Cardinali Fred , Blount Ben C.
Published: July 2010

Almost a billion persons lack access to improved drinking water, and diarrheal diseases cause an estimated 1.87 million deaths per year. Sodium dichloroisocyanurate (NaDCC) tablets are widely recommended for household water treatment to reduce diarrhea. Because NaDCC is directly added to untreated water sources, concerns have been raised about the potential health impact of disinfection by-products. This study investigated trihalomethane (THM) production in water from six sources used for drinking (0.6–888.5 nephelometric turbidity units) near Arusha, Tanzania. No sample collected at 1, 8, and 24 hours after NaDCC addition exceeded the World Health Organization guideline values for either individual or total THMs. Ceramic filtration, sand filtration, cloth filtration, and settling and decanting were not effective mitigation strategies to reduce THM formation. Chlorine residual and THM formation were not significantly different in NaDCC and sodium hypochlorite treatment. Household chlorination of turbid and non-turbid waters did not create THM concentrations that exceeded health risk guidelines.
Association of Pica with Anemia and Gastrointestinal Distress among Pregnant Women in Zanzibar, Tanzania
Authors: Young Sera L. , Khalfan Sabra S. , Farag Tamer H. , Kavle Justine A. , Ali Said M. , Hajji Hamad , Rasmussen Kathleen M. , Pelto Gretel H. , Tielsch James M. , Stoltzfus Rebecca J.
Published: July 2010

The etiology of pica, the purposive consumption of non-food substances, is not understood, despite its ubiquity among gravidae. We examined correlates of pica in a representative obstetric population (n = 2,368) on Pemba Island, Zanzibar, Tanzania to examine proposed etiologies. Cross-sectional data were collected on socioeconomic characteristics, food intake, geophagy (earth consumption), amylophagy (raw starch consumption), anthropometry, iron status, parasitic burden, and gastrointestinal morbidities. Amylophagy was reported by 36.3%, geophagy by 5.2%, and any pica by 40.1%. There was a strong additive relationship of geophagy and amylophagy with lower hemoglobin (Hb) concentration and iron deficiency anemia. By multivariate logistic regression, any pica was associated with Hb level (odds ratio [OR] = 0.76, 95% confidence interval [CI] = 0.72–0.81), nausea (OR = 1.45, 95% CI = 1.20–1.73), and abdominal pain (OR = 1.22, 95% CI = 1.01–1.48). These striking results indicate that the nature of the relationship between pica, pregnancy, gastrointestinal distress, and iron deficiency anemia merits further investigation.
A 40-Year-Old Man with Ulcerated Skin Lesions Caused by Bites of Safari Ants
Authors: Chianura Leonardo , Pozzi Federica
Published: July 2010

We report a 40-year old man in Uganda with ulcerated skins lesions, hypotension, and anaphylaxis caused by bites of safari ants. Treatment was successful. Physicians should be aware of anaphylaxis caused by ant bites.
Interruption of Transmission of Onchocerca volvulus in the Oaxaca Focus, Mexico
Authors: Rodríguez-Pérez Mario A. , Unnasch Thomas R. , Domínguez-Vázquez Alfredo , Morales-Castro Alba L. , Peña-Flores Graciela P. , Orozco-Algarra María E. , Arredondo-Jiménez Juan I. , Richards Frank , Vásquez-Rodríguez Miguel A. , Rendón Vidal García
Published: July 2010

All endemic communities of the Oaxaca focus of onchocerciasis in southern Mexico have been treated annually or semi-annually with ivermectin since 1994. In-depth epidemiologic assessments were performed in communities during 2007 and 2008. None of the 52,632 Simulium ochraceum s.l. collected in four sentinel communities was found to contain parasite DNA when tested by polymerase chain reaction-enzyme-linked immunosorbent assay (PCR-ELISA), resulting in an upper bound of the infection rate in the vectors of 0.07/2,000. The prevalence of microfilariae (mf) in the cornea and/or anterior chamber of the eye was also zero (0 of 1,039 residents examined; 95%-UL = 0.35%). Similarly, all 1,164 individuals examined by skin biopsy were mf negative (95%-UL = 0.31%), and sera collected from 3,569 children from 25 communities did not harbor Ov16 IgG4-antibodies (95%-UL = 0.09%). These meet the criteria for absence of morbidity and parasite transmission in the Oaxaca focus. As a result mass treatments with ivermectin were halted in 2009.
Antimicrobial Drug Resistance Trends of Bacteremia Isolates in a Rural Hospital in Southern Mozambique
Authors: Mandomando Inácio , Sigaúque Betuel , Morais Luis , Espasa Mateu , Vallès Xavier , Sacarlal Jahit , Macete Eusébio , Aide Pedro , Quintò Llorenç , Nhampossa Tacilta , Machevo Sónia , Bassat Quique , Menéndez Clara , Ruiz Joaquim , Roca Anna , Alonso Pedro L.
Published: July 2010

Antibiotic resistance in Africa is increasing but insufficiently recognized as a public health problem. However, there are scarce data for antimicrobial resistance trends among bloodstream isolates in sub-Saharan Africa. Antimicrobial drug resistance trends among bacteria isolated from blood of children < 15 years of age admitted to the Manhiça District Hospital in Mozambique during May 2001–April 2006 were monitored by disk diffusion. We documented a linear trend of increasing resistance throughout the study period to chloramphenicol among isolates of Non-typhi Salmonella (P < 0.001), Escherichia coli (P = 0.002), Staphylococcus aureus (P < 0.001), and Haemophilus influenzae (P < 0.001). Increasing resistance to ampicillin was also observed for H. influenzae isolates (P < 0.001). We report trends of increasing resistance among the most frequent etiologies of bacteremia to the most commonly used antibiotics for empirical therapy in this community. Quinolones and third-generation cephalosporines may be needed in the short term to manage community-acquired infections.
The Platelet Count in Cerebral Malaria, Is It Useful to the Clinician?
Authors: Chimalizeni Yamikani , Kawaza Kondwani , Taylor Terrie , Molyneux Malcolm
Published: July 2010

We conducted this study to determine the prognostic significance of the platelet count in children with cerebral malaria. We studied children with cerebral malaria admitted to the pediatric research ward at Queen Elizabeth Central Hospital, Malawi. We analyzed 1,811 children with cerebral malaria and compared them with 521 children with bacterial meningitis. There was a significant difference in platelet counts between children with cerebral malaria and those with meningitis. Among children with cerebral malaria, there was no relationship between the platelet count and either the admission coma score or the eventual outcome. Those with malarial retinopathy were more thrombocytopenic than those without. Our results suggest that the platelet count is not prognostic in Malawian children with cerebral malaria.
Lack of Active Onchocerca volvulus Transmission in the Northern Chiapas Focus of Mexico
Authors: Rodríguez-Pérez Mario A. , Unnasch Thomas R. , Domínguez-Vázquez Alfredo , Morales-Castro Alba L. , Richards Frank , Peña-Flores Graciela P. , Orozco-Algarra María Eugenia , Prado-Velasco Gibert
Published: July 2010

The northern Chiapas onchocerciasis focus has undergone 11 years of ivermectin mass treatment. No evidence of microfilariae in the cornea and/or anterior chamber of the eye or in skin snips was seen in residents examined in 2006 in two sentinel communities (upper limit of the 95% confidence interval [UL 95% CI] = 0.5% and 0.3%, respectively). In children 10 and under, 0 of 305 were found to harbor antibodies to Ov16, a marker of parasite exposure; 0 of 4,400 Simulium ochraceum s.l. collected in 2005 contained parasite DNA, giving an UL 95% CI for the infective rate of 0.9/2,000, and an UL 95% CI of the seasonal transmission potential of 1.2 L3/person. These data, assumed to be representative of the focus as a whole, suggest that there is no ongoing transmission of Onchocerca volvulus in the northern Chiapas focus. Community-wide treatments with ivermectin were halted in 2008, and a post-treatment surveillance phase was initiated.
Comparative Diagnosis of Malaria Infections by Microscopy, Nested PCR, and LAMP in Northern Thailand
Authors: Pöschl Birgit , Waneesorn Jarurin , Thekisoe Oriel , Chutipongvivate Salakchit , Panagiotis Karanis
Published: July 2010

Three methods, microscopy, nested polymerase chain reaction (nPCR), and loop-mediated isothermal amplification (LAMP) have been applied for malaria diagnosis in 105 human blood samples collected in Northern Thailand. Only Plasmodium falciparum and Plasmodium vivax infections were detected. A total number of 57 positives (54%) could be detected for P. falciparum and 25 (24%) for P. vivax when all samples that were positive in any of the three methods are counted together. The nPCR was used as a reference standard for comparison with the other methods, microscopy and LAMP. The sensitivity of LAMP for P. falciparum was 100%. All nPCR-negative samples for P. falciparum were also negative by both microscopy and LAMP (specificity, 100%). For diagnosis of P. vivax, microscopy detected 15 of 23 nPCR-positive samples (sensitivity, 65%). LAMP detected 22 of 23 nPCR-positives (sensitivity, 96%). Among the 82 nPCR-negative samples microscopy detected two samples (specificity, 98%). All 82 nPCR-negative were also negative by the LAMP method (specificity, 100%). Both Plasmodium genus- and species-specific LAMP primer sets yielded the same results in all samples. There were no significant differences in the prevalence detected by each method. We assume that LAMP was as reliable as nPCR and more reliable than microscopy in the detection of Plasmodium DNA tested in the examined Thai field blood samples. This study further validates LAMP as an alternative molecular diagnostic tool, which can be used in the diagnosis of early infections of malaria cases and together with nPCR can also be used as supplementary methods for clinical and epidemiological use.
Cost Savings with Rapid Diagnostic Tests for Malaria in Low-Transmission Areas: Evidence from Dar es Salaam, Tanzania
Authors: Yukich Joshua , D'Acremont Valerie , Kahama Judith , Swai Ndeniria , Lengeler Christian
Published: July 2010

Rapid diagnostic tests (RDTs) for malaria may help rationalize antimalarial drug use. However, the economic effects of these tests may vary. Data on costs were collected from 259 patients in 6 health facilities by using exit and in-charge interviews and record reviews during a trial of RDT rollout in Dar es Salaam, Tanzania. The RDTs decreased patient expenditure on drugs (savings = U.S. $0.36; P = 0.002) and provider drug costs (savings = U.S. $0.43; P = 0.034) compared with control facilities. However, RDT introduction did not significantly reduce patients' overall expenditures (U.S. $1.02, 95% confidence interval [CI] = $0.76–$1.36 versus U.S. $1.33 95% CI = $0.99–$1.77) and may increase total provider costs (U.S. $3.63, 95% CI = $3.40–$3.89 versus U.S. $2.32, 95% CI = $1.99–$2.69) compared with control facilities. Clinician's compliance with test results was higher with RDTs than with routine microscopy (95% versus 82%; P = 0.002). The RDTs reduced drug costs in this setting but did not offset the cost of the tests, although they also resulted in non-monetary benefits, including improved management of patients and increased compliance with test results.
Adrenal Function Status in Patients with Paracoccidioidomycosis after Prolonged Post-Therapy Follow-Up
Authors: Tobón Angela M. , Agudelo Carlos A. , Restrepo Carlos A. , Villa Carlos A. , Quiceno William , Estrada Santiago , Restrepo Angela
Published: July 2010

This study assessed adrenal function in patients with paracoccididioidomycosis who had been treated to determine a possible connection between high antibody titers and adrenal dysfunction attributable to persistence of the fungus in adrenal gland. Adrenal gland function was studied in 28 previously treated patients, 2 (7.1%) of whom were shown to have adrenal insufficiency and 7 (259%) who showed a below normal response to stimuli by adrenocorticotropic hormone. Paracoccidioides brasiliensis was detected in the adrenal gland from one of the patients with adrenal insufficiency. Although the study failed to demonstrate a significant difference between high antibody titers and low cortisol levels, the proportion of adrenal insufficiency detected and the subnormal response to adrenocorticotropic hormone confirmed that adrenal damage is an important sequela of paracoccidioidomycosis. Studies with a larger number of patients should be conducted to confirm the hypothesis of persistence of P. brasiliensis in adrenal gland after therapy.
Human Antibody Response to Anopheles gambiae Saliva: An Immuno-Epidemiological Biomarker to Evaluate the Efficacy of Insecticide-Treated Nets in Malaria Vector Control
Authors: Drame Papa M. , Poinsignon Anne , Besnard Patrick , Le Mire Jacques , Dos-Santos Maria A. , Sow Cheikh S. , Cornelie Sylvie , Foumane Vincent , Toto Jean-Claude , Sembene Mbacké , Boulanger Denis , Simondon François , Fortes Filomeno , Carnevale Pierre , Remoue Franck
Published: July 2010

For the fight against malaria, the World Health Organization (WHO) has emphasized the need for indicators to evaluate the efficacy of vector-control strategies. This study investigates a potential immunological marker, based on human antibody responses to Anopheles saliva, as a new indicator to evaluate the efficacy of insecticide-treated nets (ITNs). Parasitological, entomological, and immunological assessments were carried out in children and adults from a malaria-endemic region of Angola before and after the introduction of ITNs. Immunoglobulin G (IgG) levels to An. gambiae saliva were positively associated with the intensity of An. gambiae exposure and malaria infection. A significant decrease in the anti-saliva IgG response was observed after the introduction of ITNs, and this was associated with a drop in parasite load. This study represents the first stage in the development of a new indicator to evaluate the efficacy of malaria vector-control strategies, which could apply in other arthropod vector-borne diseases.
First Evidence of High Knockdown Resistance Frequency in Anopheles arabiensis (Diptera: Culicidae) from Ethiopia
Authors: Yewhalaw Delenasaw , Bortel Wim Van , Denis Leen , Coosemans Marc , Duchateau Luc , Speybroeck Niko
Published: July 2010

The status of knockdown resistance (kdr) mutation was investigated in the major malaria vector Anopheles arabiensis Patton (Diptera: Culicidae) from Ethiopia. Among 240 mosquito samples from 15 villages of southwestern Ethiopia that were screened by allele-specific polymerase chain reaction for kdr mutations, the West African kdr mutation (L1014F) was detected in almost all specimens (98.5%), whereas the East African kdr mutation (L1014S) was absent. Moreover, the mortality of An. gambiae s.l. to diagnostic dosages of 4% DDT, 0.75% permethrin, and 0.05% deltamethrin from bioassay results was 1.0%, 18.1%, and 82.2%, respectively. We report here the highest kdr allele frequency ever observed in An. arabiensis and its implications in malaria vector control in Ethiopia are discussed.
Divergent Roles of IRAK4-Mediated Innate Immune Responses in Two Experimental Models of Severe Malaria
Authors: Finney Constance A. M. , Lu Ziyue , Hawkes Michael , Yeh Wen-Chen , Liles W. Conrad , Kain Kevin C.
Published: July 2010

Severe malaria represents a clinical spectrum of disease. We propose that innate immune inflammatory responses to malaria play key roles in the pathogenesis and clinical outcomes of distinct severe malaria syndromes. To investigate this hypothesis, mice deficient in IRAK4, central to Toll-like receptor (TLR)-mediated signaling, were studied in two experimental models of malaria: Plasmodium berghei (PbA) and Plasmodium chabaudi (PccAS). Irak4–/–mice had decreased pro-inflammatory cytokine production during infection in both models. However, animals were relatively protected from PbA-associated symptoms compared with wild-type mice, whereas Irak4–/– animals were more susceptible to PccAS-associated disease. These results show that IRAK4-mediated innate immune inflammatory responses play critical roles in divergent clinical outcomes in murine malaria models. As such, integrated approaches, using more than one model, are required to fully understand the parasite/host interactions that characterize severe malaria, and more importantly, to fully assess the effect of adjunctive therapies targeting innate immune responses to malaria.
Clinical Features of Bowel Anisakiasis in Japan
Authors: Yasunaga Hideo , Horiguchi Hiromasa , Kuwabara Kazuaki , Hashimoto Hideki , Matsuda Shinya
Published: July 2010

Bowel anisakiasis is rare, and the incidence and clinical features of this condition remain unclear. Using the Japanese Diagnosis Procedure Combination (DPC) in-patient database, we identified 201 cases of bowel anisakiasis between the months of July and December during 2007 and 2008. More than 70% were males. The average age was 54.5 years. Overall, 102 (50.7%) cases had ileus, 16 (8.0%) had perforation or peritonitis, and 4 (2.0%) had intestinal bleeding. Allergic responses, including urticaria, were found in seven (3.5%) patients. Fourteen (7.0%) cases underwent open surgery. Three (1.5%) underwent colonoscopic removal of Anisakis larvae. The average length of stay in the hospital was 9.6 days. The annual incidence of bowel anisakiasis is estimated to be about 3.0 per 1 million people per year. It is important to continue collecting all available data to monitor the trends of this distressing condition.
Incubation Periods of Yellow Fever Virus
Authors: Johansson Michael A. , Arana-Vizcarrondo Neysarí , Biggerstaff Brad J. , Staples J. Erin
Published: July 2010

Yellow fever virus is a global health threat due to its endemicity in parts of Africa and South America where human infections occur in residents and travelers. To understand yellow fever dynamics, it is critical to characterize the incubation periods of the virus in vector mosquitoes and humans. Here, we compare four statistical models of the yellow fever incubation periods fitted with historical data. The extrinsic incubation period in the urban vector Aedes aegypti was best characterized with a temperature-dependent Weibull model with a median of 10 days at 25°C (middle 95% = 2.0–37 days). The intrinsic incubation period, fitted with a log-normal model, had a median of 4.3 days (middle 95% = 2.3–8.6 days). These estimates and their associated statistical models provide a quantitative basis to assist in exposure assessments, model potential outbreaks, and evaluate the effectiveness of public health interventions.
Cardiac Hydatidosis
Authors: Neuville Mathilde , Grisoli Dominique , Nicoud Alexane , Jacquier Alexis , Lagier Jean-Christophe , Collart Frédéric , Thomas Pascal , Parola Philippe
Published: July 2010

We report a case of an adult who developed superior vena cava syndrome because of cardiac hydatidosis. A 37-year-old man from Morocco developed progressive dyspnoea and cough. Cardiac hydatidosis was diagnosed because of both the typical radiological findings and the positive serology for echinococcosis. The patient was treated by surgery and albendazole without complications.
In situ determination of the quantum yield of phytoplankton chlorophyll a fluorescence: A simple algorithm, observations, and a model
Authors: Morrison J. Ruairidh
Published: July 2010

Vertical profiles of the in situ quantum yield of fluorescence of chlorophyll a, φf, were derived with an algorithm from spectral underwater radiometer measurements. Select inherent optical properties were obtained from an initial radiance reflectance inversion that was optimized by comparing retrieved estimates of phytoplankton absorption with independent measurements. The comparison of chlorophyll concentrations produced by the algorithm to measured values allowed validation of the inversion. Fluorescence quantum yield values were calculated from the retrieved phytoplankton absorption and the upwelling radiance corrected for elastic and inelastic scattering. Raman scattered light was found to be a significant component of the upwelling light field at wavelengths of Chl a fluorescence. Values of φf determined using the algorithm, and therefore derived solely from the radiometer measurements, were not significantly different from those estimated using independent measurements of absorption by phytoplankton (r2 = 0.86). The profiles of φf were characterized by an initial increase with depth to a subsurface maximum followed by a subsequent decrease. The irradiances of the subsurface maxima and φf at high irradiances appeared to be well conserved. An irradiance‐based model including photochemical and nonphotochemical quenching was developed to explain variations in the quantum yield.
Evolution of rotifers in saline and subsaline lakes: A molecular phylogenetic approach
Authors: Derry Alison M. , N. Hebert Paul D. , Prepas Ellie E.
Published: July 2010

Evolutionary relationships within the phylum Rotifera are poorly understood despite the important role that they play in freshwater ecosystems. Phylogenetic analyses of DNA sequences from two mitochondrial genes, 16S rDNA and cytochrome oxidase I (COI), were employed to examine the extent of genetic divergence within populations of several common taxa. This work sought to verify the role of phenotypic plasticity versus genetic variation in explaining the morphological variation in some taxa. Deep genetic divergence (4.4% COI nucleotide sequence divergence) was detected between spined and unspined forms of Keratella cochlearis, which suggests that they represent different species. However, morphological variation in K. hiemalis appeared to be environmentally induced. The study also sought to ascertain the role of one environmental variable, salinity, in the patterning of sequence variation. Greater haplotype diversity and genetic divergence were observed among populations of halophilic Brachionus plicatilis than among freshwater Keratella quadrata populations from northern Canada. When COI DNA sequences for B. plicatilis haplotypes were compared with those from Spain, there was evidence for considerable genetic diversity within this species among closely located saline lakes in northern Canada.
Anomalously low zooplankton abundance in the Ross Sea: An alternative explanation
Authors: Tagliabue Alessandro , Arrigo Kevin R.
Published: July 2010

The southwestern Ross Sea (Antarctica) supports a large bloom of Phaeocystis antarctica in the Ross Sea polynya, which is impacted minimally by zooplankton and a smaller diatom bloom in the adjacent Terra Nova Bay polynya, which are more readily grazed. This difference in grazing pressure between the two regions frequently has been explained by a reduced susceptibility of P. antarctica to grazing, despite conflicting evidence showing that Phaeocystis spp. are readily grazed by zooplankton. Using a three‐dimensional ecosystem model of the Ross Sea, our goal was to determine whether phytoplankton growth dynamics, rather than mechanical and/or chemical defenses, might explain (1) the relatively low zooplankton abundance observed in waters dominated by P. antarctica, and (2) the low overall zooplankton biomass in the Ross Sea. Although in the model, diatoms and P. antarctica were grazed with equal ease (i.e., no prey selectivity), the slower growth of phytoplankton in Terra Nova Bay resulted in a higher degree of phytoplankton‐zooplankton coupling and greater zooplankton abundance. Conversely, the exaggerated boom/bust cycle of the P. antarctica bloom in the Ross Sea polynya resulted in greater decoupling from higher trophic levels and reduced zooplankton biomass. This indicates that the low zooplankton abundance observed in the Ross Sea polynya may be a consequence of their inability to match the high growth rates of P. antarctica. The different degrees of zooplankton‐phytoplankton coupling between Terra Nova Bay and the Ross Sea polynya may have important implications for food web structure and carbon export, especially under changing stratification.
Microbial degradation of peptidoglycan in seawater
Authors: Nagata T. , Meon B. , L. Kirchman D.
Published: July 2010

A constituent of the bacterial cell wall, peptidoglycan, has been suggested to be a significant fraction of marine dissolved organic matter, but little is known about its turnover. We measured hydrolysis and remineralization rates of peptidoglycan in surface waters by using radiolabeled peptidoglycan that was extracted from a Gram‐negative bacterium. Polysaccharide (N‐acetyl‐glucosamine and N‐acetyl‐muramic acids) and peptide (D‐glutamate) components of peptidoglycan were specifically radiolabeled. Purity of the preparations and specificity of labeling were ascertained by high‐performance liquid chromatography. First‐order kinetic constants of peptidoglycan remineralization were 2–21 times lower than those of proteins. The turnover time of peptidoglycan was estimated to be 10–167 d, indicating its semilabile nature. The two main components of peptidoglycan are degraded differently; the remineralization rate of the peptide component was three times greater than that of the polysaccharide moiety. Chemically modified, low‐molecular‐weight material was produced during the degradation of the polysaccharide component, but not during degradation of protein. These results indicate that peptidoglycan is less degradable than proteins in marine environments and are consistent with observations that D/L‐isomer ratios of amino acids increase during early diagenesis.
Global estimates of enhanced solute transport in marine sediments
Authors: Meile Christof , Cappellen Philippe Van
Published: July 2010

Pore‐water solute transport processes acting in addition to molecular diffusion affect sediment biogeochemistry and benthic exchange fluxes. Given the relatively few direct measurements of enhanced transport intensities, there is a need for predictive relationships to calculate enhanced transport parameters from more readily available information. Here, enhanced diffusion coefficients and nonlocal mass transfer coefficients are obtained by comparing total and molecular diffusion fluxes of oxygen across the sediment‐water interface. Semiempirical relationships for these coefficients are derived as functions of benthic oxygen uptake. According to these relationships, enhanced solute transport significantly affects sediment‐water column exchanges in regions with large benthic oxygen fluxes, typically on the continental shelves. On a global scale, enhanced transport contributes approximately one third of the total benthic flux of oxygen and more than half of that of phosphate.
Sea urchin spawning in benthic boundary layers: Are eggs fertilized before advectingaway from females?
Authors: Yund Philip O. , Meidel Susanne K.
Published: July 2010

Past work on fertilization in echinoids and other egg‐broadcasting, free‐spawning invertebrates suggests that these organisms might be extremely sperm limited in the field unless individuals spawn in close proximity and under nearly ideal flow conditions. However, virtually all previous experiments have used one or more techniques (surrogates for males and females, and short sampling duration) that bypassed two potentially important aspects of echinoid reproductive biology: the release of gametes in viscous fluids that cling to tests and spines, and extended longevity of eggs and undiluted sperm. We hypothesized that these attributes might interact with some flow regimes to facilitate time‐integrated fertilization. Consequently, we explored fertilization processes in sea urchins induced to spawn in a benthic boundary layer in a flow‐through flume, with a male 0.5 m upstream of a female. Our observations and data suggest that at free‐stream flow velocities of 2.5 and 8.5 cm s‐1, gametes were slowly and continually advected from the aboral surfaces of spawning animals. Eggs on the surface of the aboral mass were often fertilized before they ablated from the surface; many advected eggs were fertilized after being trapped in the vortex downstream of the female. Gamete advection and fertilization continued for several hours, with the actual time course depending on flow velocity. Fertilization levels declined only slightly with increasing flow velocity. These results suggest that fertilization in echinoderms and other free‐spawners with viscous, long‐lived gametes could be much less sperm‐limited than currently envisioned and have additional implications for population dynamics and selection on gamete characteristics.
Why the phosphorus retention of lakes does not necessarily depend on the oxygen supply to their sediment surface
Authors: Gächter René , Müller Beat
Published: July 2010

In order to improve the trophic state of Lake Sempach, a eutrophied lake in central Switzerland, its external phosphorus (P) load has been decreased and its hypolimnion has been artificially oxygenated to lower the lake‐internal P recycling. Based on more than 15 yr of experience, we conclude that the reduction of the external P load resulted in a corresponding decrease of the lake’s P concentration. However, contrary to initial expectations, increased hypolimnetic dissolved oxygen concentrations neither (1) reduced the P release from sediments during summer nor (2) resulted in anincreased permanent P retention. These observations warrant a reevaluation of the well‐accepted management strategy of decreasing the lake internal P cycling by maintaining an aerobic hypolimnion and sediment surface. We hypothesize that oxygenation only results in an increased permanent benthic P burial if, because of the depressed sulfide production, more ferrous phosphate (e.g., vivianite) and less FeS is deposited in the anoxic sediment. Hence, it is not the oxic sediment surface that directly affects the permanent redox‐dependent sediment P retention but the molar ratio of the available reactive Fe(II) : S2‐ : PO4 in the anoxic sediment. This ratio is driven by the settling rate and the nature of organic matter and particulate iron, as well as the supply of oxygen, nitrate, and sulfate to the sediment.
Induction of sexual reproduction in Brachionus plicatilis (Monogononta, Rotifera) by a density‐dependent chemical cue
Authors: Stelzer C. P. , Snell T. W.
Published: July 2010

Induction of mixis (sexual reproduction) in rotifers of the genus Brachionus is believed to be triggered by a chemical that is released into the water and accumulates at high population densities. However, direct and conclusive evidence for this hypothesis is thus far lacking. In this study, two mass cultures of the rotifer Brachionus plicatilis were monitored as they grew from low to high population densities. Conditioned water was prepared daily from these cultures, and females were exposed in a bioassay, which consisted of juvenile Brachionus, cultured individually in large volumes that would normally suppress mixis. Conditioned water induced mixis in the bioassay at rates comparable to those found in the mass cultures. Both in bioassay and mass cultures, mixis was essentially absent in the beginning of the experiment, when population densities were very low. The first mictic females appeared at densities of 0.1 females ml-1, and their proportion increased rapidly as the populations grew to ≫1 female ml-1. The maximum rates of mixis in the bioassay were highly significant and reached 51% of those observed in the mass cultures. These results strongly support the hypothesis that mixis in Brachionus plicatilis is induced by a density‐dependent chemical cue.
Predicting the response of Gulf of Mexico hypoxia to variations in Mississippi River nitrogen load
Authors: Scavia Donald , Rabalais Nancy N. , Turner R. Eugene , Justić Dubravko , Wiseman William J.
Published: July 2010

The effects of nutrient loading from the Mississippi River basin on the areal extent of hypoxia in the northern Gulf of Mexico were examined using a novel application of a dissolved oxygen model for a river. The model,driven by river nitrogen load and a simple parameterization of ocean dynamics, reproduced 17 yr of observed hypoxia location and extent, subpycnocline oxygen consumption, and cross‐pycnocline oxygen flux. With Monte Carlo analysis, we illustrate through hindcasts back to 1968 that extensive regions of low oxygen were not common before the mid‐1970s. The Mississippi River Watershed/Gulf of Mexico Hypoxia Task Force set a goal to reduce the 5‐yr running average size of the Gulf’s hypoxic zone to less than 5,000 km2 by 2015 and suggested that a 30% reduction from the 1980–1996 average nitrogen load is needed to reach that goal. Here we show that 30% might not be sufficient to reach that goal when year‐to‐year variability in ocean dynamics is considered.
Modeling circulation in lakes: Spatial and temporal variations
Authors: Laval Bernard , Imberger Jörg , Hodges Ben R. , Stocker Roman
Published: July 2010

The influence of spatial and temporal variations in wind forcing on the circulation in lakes is investigated using field data and the three‐dimensional Estuary and Lake Computer Model (ELCOM) applied to Lake Kinneret. Lake Kinneret field data from six thermistor chains and eight wind anemometers deployed during July 2001 are presented. Internal wave motions are well reproduced by the numerical model when forced with a spatially uniform wind taken from a station near the lake center; however, simulated seiche amplitudes are too large (especially vertical mode 2) and lead observations by 3–10 h (for a 24‐h period wave) at different locations around the lake. Consideration of the spatial variation of the wind field improves simulated wave amplitude, and phase error at all stations is reduced to less than 1.5 h. This improvement is attributable to a better representation of the horizontally averaged wind stress and can be reproduced with a spatially uniform wind that has the same horizontally averaged wind stress as the spatially varying wind field. However, a spatially varying wind field is essential for simulating mean surface circulation, which is shown to be predominantly directly forced by the surface‐layer‐averaged wind stress moment.
Food uptake in the harmful alga Prymnesium parvum mediated by excreted toxins
Authors: Skovgaard Alf , Hansen Per Juel
Published: July 2010

Toxin production is widespread among aquatic microalgae, suggesting a functional advantage for organisms producing toxic compounds. However, the biological role of algal toxin production is only vaguely understood. Here, we show that excretion of a toxic substance in the phagotrophic phytoflagellate Prymnesium parvum (Prymnesiophyceae) constitutes a mechanism to immobilize and seize motile prey. Feeding frequency of P. parvum in dilute batch cultures was low when fed the motile prey Heterocapsa rotundata (dinoflagellate). However, dense cultures caused immobilization of H. rotundata cells, thereby allowing P. parvum to feed on them. In contrast, when fed a nonmotile prey—the diatom Thalassiosira pseudonana—feeding frequency was high, even in dilute P. parvum cultures. We could demonstrate that feeding frequency of P. parvum on H. rotundata was positively correlated with the measure of the toxic effect causing immobilization and lysis of prey cells. The fact that the toxic effect on H. rotundata was found in cell‐free filtrate of P. parvum cultures suggests that immobilization and lysis of prey cells were caused by the excretion of toxins.
Experimental investigation of taxon‐specific response of alkaline phosphatase activity in natural freshwater phytoplankton
Authors: Rengefors K. , Ruttenberg K. C. , Haupert C. L. , Taylor C. , Howes B. L. , Anderson D. M.
Published: July 2010

It is widely accepted that alkaline phosphatase activity (APA) is an efficient indicator of phosphate limitation in freshwater phytoplankton communities. In this study, we investigated whether the response in APA to phosphate limitation differs among the taxa in a mixed phytoplankton assemblage. We used the new enzyme‐labeled fluorescence (ELF) technique, which allows microscopic detection of phosphate limitation in individual cells of multiple species. The most prominent findings of this study were that alkaline phosphatase (AP) was induced in many, but not all taxa and that different taxa, as well as different cells within a single taxon, experienced different degrees of phosphate stress under the same environmental conditions. Our approach was to manipulate the limiting nutrient in a natural freshwater phytoplankton community by incubating lake water in the laboratory. We induced nitrogen (N) or phosphate limitation through additions of inorganic nutrients. Both the ELF assay and bulk APA indicated that the lake phytoplankton were not phosphate limited at the start of the experiment. During the experiment, several chlorophyte taxa (e.g., Eudorina and an unidentified solitary spiny coccoid) were driven to phosphate limitation when inorganic N was added, as evidenced by a higher percentage of ELF‐labeled cells relative to controls, whereas other chlorophyte taxa such as Actinastrum and Dictyosphaerium were not phosphate stressed under these conditions. In the phosphate‐limited treatments, little or no ELF labeling was observed in any cyanobacterial taxa. Furthermore, all taxa observed after the ELF labeling procedure (<10‐µm fraction) were labeled with ELF at least on one occasion, demonstrating the wide applicability of the ELF method. By using ELF labeling in tandem with bulk APA, the resolution and analysis of phosphate limitation was increased, allowing the identification of specific phosphate‐stressed taxa.
Effect of large marine diatoms growing at low light on episodic new production
Authors: Goldman Joel C. , McGillicuddy Dennis Jr. J.
Published: July 2010

Mesoscale eddies have been shown to be a common feature of open ocean regions such as the Sargasso Sea. By lifting nutrients up to the lower portions of the euphotic zone, these eddies can cause episodic phytoplankton blooms that can lead to substantial new production. In the Sargasso Sea, it has been estimated that such blooms can account for 35%–50% of annual new production. In the present study, it was shown that a common large diatom Stephanopyxis palmeriana is capable of growing in a low‐light environment typical of the bottom 50 m of the euphotic zone at rates sufficiently high to sustain the contemporary estimates of new production that have been attributed to mesoscale eddies. The diatom was grown in laboratory batch experiments at irradiance levels from 11 to 79 µmol photons m−2 s−1, equivalent to irradiance levels occurring in the Sargasso Sea during the summer at depths from ~100 m (the 1% light level) up to 50 m. Resulting growth rates were compared with growth rates from the literature for similar large diatoms, and a simple model of new production was developed to show the dependency of new production on specific growth rate. Included in the model were other important parameters such as the depth of nutrient incursion resulting from lifting of the thermocline when an eddy passes, the duration of the bloom, and the size of the prebloom diatom population. Using realistic ranges for these parameters, it was evident from the model that there is no physiological constraint on these large diatoms from growing fast enough at very low light levels to meet the new production estimates resulting from eddies.
Assessing the potential for developing internal diatom‐based transfer functions for Lake Baikal
Authors: Mackay Anson W. , Battarbee Richard W. , Flower Roger J. , Granin Nicholas G. , Jewson David H. , Ryves David B. , Sturm Michael
Published: July 2010

We explore possible quantitative relationships between diatom species and environmental data for Lake Baikal using multivariate techniques. Our approach differs from published studies in other regions (on training sets and transfer functions) because (1) although only one lake is examined, we use the internal lake gradients rather than gradients among lakes and (2) the majority of the dominant diatom taxa are endemic. Canonical correspondence analysis on 93 surface sediment diatom assemblages reveals that major taxa show distinct relationships with measured environmental variables. Five significant variables were identified: snow thickness on ice (which accumulates on the frozen lake surface between January and April/May), water depth, suspended matter, annual solar radiation, and mean July temperature of surface waters. The strongest relationship is with snow thickness, which influences light levels in the water below the ice. A diatom‐based inference model has been developed to predict snow thickness on the ice using weighted averaging (WA) and WA with tolerance down‐weighting (WAtol) models. Results suggest that Lake Baikal diatom assemblages in surface sediments can be used to develop a robust model for estimating snow thickness across frozen Lake Baikal (r2jack = 0.607, RMSEP = 0.138 log cm). This model has potential applications for recent paleoclimate studies in this region of continental Eurasia.
Simple mixing criteria for the growth of negatively buoyant phytoplankton
Authors: O'Brien Katherine R. , Ivey Gregory N. , Hamilton David P. , Waite Anya M. , Visser Petra M.
Published: July 2010

Phytoplankton population dynamics are controlled by the relative rather than absolute timescales of mixing, growth, and loss processes such as sedimentation, grazing, and so on. Here, the vertical distribution and biomass of phytoplankton populations are quantified by two timescale ratios: the Peclet number Pe—the ratio of mixing and sedimentation timescales—and the growth number G—the ratio of sedimentation and net growth timescales. Three mixing regimes are defined for phytoplankton and other particles. For Pe ≥ 100, the population is translated linearly down the water column over time and will leave the surface mixing layer completely after sedimentation timeτts. For 0.1 <Pe <100, the population distribution depends on the relative magnitude of Pe and G. Finally, for Pe≤ 0.1, the population will be vertically uniform, and biomass changes exponentially over time with characteristic timescale=c =—s/(G —1). This analysis is valid for negatively buoyant phytoplankton, except when mixing time is much longer than growth time and Pe≤ 0.1, which can occur for very slow sinking species. These regimes can be used for assessing the effect of changes in the mixing, growth, or sedimentation conditions on population dynamics. Published data from a lake and diurnally stratified river weir pool are used here to verify a minimum thermocline depth hypothesis proposed by others. Mixing and growth regimes are used to calculate minimum mixing depth hmin and to determine phytoplankton sinking rates from published sediment trap data.
Stable isotope biogeochemistry of methane formation in profundal sediments of Lake Kinneret (Israel)
Authors: Nüsslein B. , Eckert W. , Conrad R.
Published: July 2010

Methane production in profundal sediments of Lake Kinneret was recently found to be, to a large extent, syntrophically coupled to the oxidation of acetate, an apparently unique feature of CH4 biogeochemistry in lake sediments. Our measurements of the conversion of 14CO2 and of [2‐14C]acetate to CH4 at both 15 and 30°C were in agreement with this observation. Measurement of the fraction of 14CO2‐derived CH4 together with δ13CH4 and δ13CO2 allowed the calculation of δ13CH4 values originating from either CO2 ( δmc) or acetate ( δma). Assuming α‐values for 13C fractionation during CO2 reduction to CH4 of 1.06–1.07, CH4 production from acetate required a relatively large fractionation factor that increased with depth and resulted in a dma from ‐50 to ‐60‰. This result is consistent with syntrophic acetate conversion to CH4 rather than acetoclastic methanogenesis. The apparent fractionation factor ( α) between CO2 and CH4 increased with depth from 1.045 to 1.065. The δ13C of sedimentary particulate organic matter increased with depth from ‐28 to ‐24‰. Incubation of sediment samples from layers in the upper 5 cm resulted in a steady increase of α, both at 15 and 30°C. Unlike deeper sediment layers, it remained constant, with δ13CH4 decreasing with incubation time. This behavior is indicative of sediments in which methanogenesis is extremely limited by substrate. Collectively, our experiments demonstrate the usefulness of 13C data to elucidate the pathway of CH4 production and confirm the unique biogeochemical features of CH4 biogeochemistry in Lake Kinneret.