Upward nitrate transport by phytoplankton in oceanic waters : balancing nutrient budgets in oligotrophic seas

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PeerJ 2 (2014): e302, doi:10.7717/peerj.302.In oceanic subtropical gyres, primary producers are numerically dominated by small (1–5 µm diameter) pro- and eukaryotic cells that primarily utilize recycled nutrients produced by rapid grazing turnover in a highly efficient microbial loop. Continuous losses of nitrogen (N) to depth by sinking, either as single cells, aggregates or fecal pellets, are balanced by both nitrate inputs at the base of the euphotic zone and N2-fixation. This input of new N to balance export losses (the biological pump) is a fundamental aspect of N cycling and central to understanding carbon fluxes in the ocean. In the Pacific Ocean, detailed N budgets at the time-series station HOT require upward transport of nitrate from the nutricline (80–100 m) into the surface layer (∼0–40 m) to balance productivity and export needs. However, concentration gradients are negligible and cannot support the fluxes. Physical processes can inject nitrate into the base of the euphotic zone, but the mechanisms for transporting this nitrate into the surface layer across many 10s of m in highly stratified systems are unknown. In these seas, vertical migration by the very largest (102–103 µm diameter) phytoplankton is common as a survival strategy to obtain N from sub-euphotic zone depths. This vertical migration is driven by buoyancy changes rather than by flagellated movement and can provide upward N transport as nitrate (mM concentrations) in the cells. However, the contribution of vertical migration to nitrate transport has been difficult to quantify over the required basin scales. In this study, we use towed optical systems and isotopic tracers to show that migrating diatom (Rhizosolenia) mats are widespread in the N. Pacific Ocean from 140°W to 175°E and together with other migrating phytoplankton (Ethmodiscus, Halosphaera, Pyrocystis, and solitary Rhizosolenia) can mediate time-averaged transport of N (235 µmol N m-2 d-1) equivalent to eddy nitrate injections (242 µmol NO3− m-2 d-1). This upward biotic transport can close N budgets in the upper 250 m of the central Pacific Ocean and together with diazotrophy creates a surface zone where biological nutrient inputs rather than physical processes dominate the new N flux. In addition to these numerically rare large migrators, there is evidence in the literature of ascending behavior in small phytoplankton that could contribute to upward flux as well. Although passive downward movement has dominated models of phytoplankton flux, there is now sufficient evidence to require a rethinking of this paradigm. Quantifying these fluxes is a challenge for the future and requires a reexamination of individual phytoplankton sinking rates as well as methods for capturing and enumerating ascending phytoplankton in the sea.This work has been funded by the National Science Foundation: OCE-0726726, OCE-0094591, OCE-9414372, OCE-9100888 and OCE-9415923 to TAV, and OCE-9423471 to CHP

Utilidad de la escala de depresión geriátrica en adultos mayores atendidos en el servicio de geriatría de la caja de seguro social

INTRODUCCIÓN. La depresión en pacientes geriátricos consiste de síntomas y características clínicas específicas que representan una condición grave que predispone a alteraciones en la funcionalidad de esta población. La Escala de Depresión Geriátrica (GDS, por su sigla en inglés), es un instrumento de tamizaje breve y de fácil aplicación, ampliamente utilizado en la clínica y la investigación para detectar síntomas depresivos. OBJETIVO. Analizar la utilidad de la GDS para detectar síntomas depresivos clínicamente relevantes en adultos mayores que acuden a la consulta externa de Geriatría del Complejo Hospitalario Dr. Arnulfo Arias Madrid (C.H.Dr.A.A.M.). METODOLOGÍA. Se realizó un estudio descriptivo de corte transversal. Se seleccionaron adultos mayores de 65 años o más del estudio Panama Aging Research Initiative (PARI). Un total de 423 participantes fueron reclutados en el estudio. De éstos, 144 participantes completaron la evaluación psiquiátrica y la GDS30 en su versión en español. RESULTADOS. El 16.7% de los participantes recibieron diagnóstico de depresión luego de la entrevista psiquiátrica. El valor predictivo positivo de la GDS-30 fue de 44.4% y el valor predictivo negativo fue de 92.6%. CONCLUSIÓN. Por el alto valor predictivo negativo de la GDS, se recomienda su uso para descartar casos en los que no existe depresión, aplicándolo como instrumento de tamizaje en los controles de salud de adultos mayores.INTRODUCCIÓN. La depresión en pacientes geriátricos consiste de síntomas y características clínicas específicas que representan una condición grave que predispone a alteraciones en la funcionalidad de esta población. La Escala de Depresión Geriátrica (GDS, por su sigla en inglés), es un instrumento de tamizaje breve y de fácil aplicación, ampliamente utilizado en la clínica y la investigación para detectar síntomas depresivos. OBJETIVO. Analizar la utilidad de la GDS para detectar síntomas depresivos clínicamente relevantes en adultos mayores que acuden a la consulta externa de Geriatría del Complejo Hospitalario Dr. Arnulfo Arias Madrid (C.H.Dr.A.A.M.). METODOLOGÍA. Se realizó un estudio descriptivo de corte transversal. Se seleccionaron adultos mayores de 65 años o más del estudio Panama Aging Research Initiative (PARI). Un total de 423 participantes fueron reclutados en el estudio. De éstos, 144 participantes completaron la evaluación psiquiátrica y la GDS30 en su versión en español. RESULTADOS. El 16.7% de los participantes recibieron diagnóstico de depresión luego de la entrevista psiquiátrica. El valor predictivo positivo de la GDS-30 fue de 44.4% y el valor predictivo negativo fue de 92.6%. CONCLUSIÓN. Por el alto valor predictivo negativo de la GDS, se recomienda su uso para descartar casos en los que no existe depresión, aplicándolo como instrumento de tamizaje en los controles de salud de adultos mayores

Summer diatom blooms in the eastern North Pacific gyre investigated with a long-endurance autonomous surface vehicle

Satellite chlorophyll a (chl a) observations have repeatedly noted summertime phytoplankton blooms in the North Pacific subtropical gyre (NPSG), a region of open ocean that is far removed from any land-derived or Ekman upwelling nutrient sources. These blooms are dominated by N2-fixing diatom-cyanobacteria associations of the diatom genera Rhizosolenia Brightwell and Hemiaulus Ehrenberg. Their nitrogen fixing endosymbiont, Richelia intracellularis J.A. Schmidt, is hypothesized to be critical to the development of blooms in this nitrogen limited region. However, due to the remote location and unpredictable duration of the summer blooms, prolonged in situ observations are rare outside of the Station ALOHA time-series off of Hawai’i. In summer, 2015, a proof-of-concept mission using the autonomous vehicle, Honey Badger (Wave Glider SV2; Liquid Robotics, a Boeing company, Sunnyvale, CA, USA), collected near-surface (<20 m) observations in the NPSG using hydrographic, meteorological, optical, and imaging sensors designed to focus on phytoplankton abundance, distribution, and physiology of this bloom-forming region. Hemiaulus and Rhizosolenia cell abundance was determined using digital holography for the entire June–November mission. Honey Badger was not able to reach the 30°N subtropical front region where most of the satellite chl a blooms have been observed, but near-real time navigational control allowed it to transect two blooms near 25°N. The two taxa did not co-occur in large numbers, rather the blooms were dominated by either Hemiaulus or Rhizosolenia. The August 2–4, 2015 bloom was comprised of 96% Hemiaulus and the second bloom, August 15–17, 2015, was dominated by Rhizosolenia (75%). The holograms also imaged undisturbed, fragile Hemiaulus aggregates throughout the sampled area at ∼10 L−1. Aggregated Hemiaulus represented the entire observed population at times and had a widespread distribution independent of the summer export pulse, a dominant annual event suggested to be mediated by aggregate fluxes. Aggregate occurrence was not consistent with a density dependent formation mechanism and may represent a natural growth form in undisturbed conditions. The photosynthetic potential index (Fv:Fm) increased from ∼0.4 to ∼0.6 during both blooms indicating a robust, active phytoplankton community in the blooms. The diel pattern of Fv:Fm (nocturnal maximum; diurnal minimum) was consistent with macronutrient limitation throughout the mission with no evidence of Fe-limitation despite the presence of nitrogen fixing diatom-diazotroph assemblages. During the 5-month mission, Honey Badger covered ∼5,690 km (3,070 nautical miles), acquired 9,336 holograms, and reliably transmitted data onshore in near real-time. Software issues developed with the active fluorescence sensor that terminated measurements in early September. Although images were still useful at the end of the mission, fouling of the LISST-Holo optics was considerable, and appeared to be the most significant issue facing deployments of this duration

High concentrations of marine snow and diatom algal mats in the North Pacific Subtropical Gyre : implications for carbon and nitrogen cycles in the oligotrophic ocean

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 52 (2005): 2315-2332, doi:10.1016/j.dsr.2005.08.004.A Video Plankton Recorder (VPR) and remotely operated vehicle (ROV) were utilized on three cruises in the oligotrophic North Pacific Subtropical Gyre (NPSG) between 1995 and 2002 to quantify the size and abundance of marine snow and Rhizosolenia diatom mats within the upper 305 m of the water column. Quantitative image analysis of video collected by the VPR and an ROV-mounted particle imaging system provides the first transect of marine snow size and abundance across the central North Pacific gyre extending from 920 km NW of Oahu to 555 km off Southern California. Snow abundance in the upper 55 m was surprisingly high for this oligotrophic region, with peak values of 6.0-13.0 x 103 aggregates m-3 at the western and eastern-most stations. At stations located in the middle of the transect (farthest from HI and CA), upper water column snow abundance displayed values of ~0.5-1.0 x 103 aggregates m-3. VPR and ROV imagery also provided in-situ documentation of the presence of nitrogen-transporting, vertically migrating Rhizosolenia mats from the surface to >300 m with mat abundances ranging from 0-10 mats m-3. There was clear evidence that Rhizosolenia mats commonly reach sub-nutricline depths. The mats were noted to be a common feature in the North Pacific gyre, with the lower salinity edge of the California Current appearing to be the easternmost extent of their oceanic distribution. Based on ROV observations at depth, flux by large (>1.5 cm) mats is revised upward 4.5 fold, yielding an average value of 40 µmol N m-2 d-1, a value equaling previous estimates that included much smaller mats visible only to towed optical systems. Our results suggest that the occurrence across a broad region of the NPSG of particulate organic matter (POM) production events represented by high concentrations of Rhizosolenia mats, associated mesozooplankton, and abundant detrital marine aggregates may represent significant stochastic components in the overall carbon, nitrogen and silica budgets of the oligotrophic subtropical gyre. Likewise, their presence has important implications for the proposed climate-driven, ecosystem reorganization or domain shift occurring in the NPSG.This project was primarily supported by NSF Biological Oceanography Program grant OCE-9423471 to C. Pilskaln, OCE-9415923 and OCE-9414372/OCE-0094591 to T. Villareal, and assisted by OCE-9314533 to D. Caron

Nitrogen fixation and transfer in open ocean diatom–cyanobacterial symbioses

Many diatoms that inhabit low-nutrient waters of the open ocean live in close association with cyanobacteria. Some of these associations are believed to be mutualistic, where N2-fixing cyanobacterial symbionts provide N for the diatoms. Rates of N2 fixation by symbiotic cyanobacteria and the N transfer to their diatom partners were measured using a high-resolution nanometer scale secondary ion mass spectrometry approach in natural populations. Cell-specific rates of N2 fixation (1.15–71.5 fmol N per cell h−1) were similar amongst the symbioses and rapid transfer (within 30 min) of fixed N was also measured. Similar growth rates for the diatoms and their symbionts were determined and the symbiotic growth rates were higher than those estimated for free-living cells. The N2 fixation rates estimated for Richelia and Calothrix symbionts were 171–420 times higher when the cells were symbiotic compared with the rates estimated for the cells living freely. When combined, the latter two results suggest that the diatom partners influence the growth and metabolism of their cyanobacterial symbionts. We estimated that Richelia fix 81–744% more N than needed for their own growth and up to 97.3% of the fixed N is transferred to the diatom partners. This study provides new information on the mechanisms controlling N input into the open ocean by symbiotic microorganisms, which are widespread and important for oceanic primary production. Further, this is the first demonstration of N transfer from an N2 fixer to a unicellular partner. These symbioses are important models for molecular regulation and nutrient exchange in symbiotic systems

Various clinical scenarios leading to development of the string sign of the internal thoracic artery after coronary bypass surgery: the role of competitive flow, a case series

<p>Abstract</p> <p>Background</p> <p>The left internal mammary artery (LIMA) is the choice for grafting of the left anterior descending coronary artery (LAD). One possible mechanism of the rare graft failure involve the presence of competitive flow.</p> <p>Method</p> <p>105 patients who had undergone coronary bypass grafting between 1998 and 2000 were included in this observational study. The recatheterizations were performed 28 months after the operations. The rate of patency the LIMA grafts was determined, and the cases with graft failure were analyzed.</p> <p>Results</p> <p>The LIMA graft was patent in 99 patients (94%). Six patients (6%) exhibited diffuse involution of the graft (string sign). The string sign was always associated with competitive flow as the basis of the LIMA graft involution. In one case quantitative re-evaluation of the preoperative coronary angiography revealed merely less than 50% diameter stenosis on the LAD with a nonligated side-branch of the LIMA. At recatheterization in two patients the pressure wire measurements demonstrated only a non-significant decrease of the fractional flow reserve (0.83 and 0.89), despite the 53% and 57% diameter stenosis in the angiogram. Another patient displayeda significant regression of the LAD lesion between the pre- and postoperative coronary angiography (from 76% to 44%) as the cause of the development of the competitive flow. In one instance, a radial artery graft on the LAD during a redo bypass operation resulted in competitive flow in the radial graft due to the greater diameter than that of the LIMA. In a further patient, competitive flow developed from a short sequential part of the LIMA graft between the nonsignificantly stenosed diagonal branch and the LAD, with involution of the main part of the graft to the diagonal branch.</p> <p>Conclusions</p> <p>The most common cause of the development of the string sign of a LIMA graft due to competitive flow is overassessment of the lesion of the LAD. Regression of a previous lesion or some other neighboring graft can also cause the phenomenon.</p

Invited Commentary: Built Environment and Obesity Among Older Adults—Can Neighborhood-level Policy Interventions Make a Difference?

Obesity is more prevalent and its consequences severe among middle-aged and older adults. Efforts to understand and address neighborhood-level causes of obesity in this population offer the potential to enhance health and reduce the costs of obesity for everyone. The accompanying paper by Li et al. (Am J Epidemiol. 2009;169(4):401–408) presents new data on the apparently significant interaction between neighborhood and individual characteristics on 1-year change in body weight and waist circumference. Despite methodological limitations in measurement, this paper supports the importance of future research that considers the complex relation between people and where they live. Efforts to design neighborhood-level policy interventions to effectively address the problem of obesity will require greater interdisciplinary collaboration

Pre-Training Muscle Characteristics of Subjects Who Are Obese Determine How Well Exercise Training Will Improve Their Insulin Responsiveness

Pre-training muscle characteristics of subjects who are obese determine how well exercise training will improve their insulin responsiveness. J Strength Cond Res 31(3): 798–808, 2017—Only half of prediabetic subjects who are obese who underwent exercise training without weight loss increased their insulin responsiveness. We hypothesized that those who improved their insulin responsiveness might have pretraining characteristics favoring a positive response to exercise training. Thirty nondiabetic subjects who were obese volunteered for 8 weeks of either strength training or endurance training. During training, subjects increased their caloric intake to prevent weight loss. Insulin responsiveness by euglycemic clamps and muscle fiber composition, and expression of muscle key biochemical pathways were quantified. Positive responders initially had 52% higher intermediate muscle fibers (fiber type IIa) with 27% lower slow-twitch fibers (type I) and 23% lower expression of muscle insulin receptors. Whether after weight training or stationary bike training, positive responders\u27 fiber type shifted away from type I and type IIa fibers to an increased proportion of type IIx fibers (fast twitch). Muscle insulin receptor expression and glucose transporter type 4 (GLUT4) expression increased in all trained subjects, but these moderate changes did not consistently translate to improvement in whole-body insulin responsiveness. Exercise training of previously sedentary subjects who are obese can result in muscle remodeling and increased expression of key elements of the insulin pathway, but in the absence of weight loss, insulin sensitivity improvement was modest and limited to about half of the participants. Our data suggest rather than responders being more fit, they may have been less fit, only catching up to the other half of subjects who are obese whose insulin responsiveness did not increase beyond their pretraining baseline

Formation of bone-like apatite layer on chitosan fiber mesh scaffolds by a biomimetic spraying process

Bone-like apatite coating of polymeric substrates by means of biomimetic process is a possible way to enhance the bone bonding ability of the materials. The created apatite layer is believed to have an ability to provide a favorable environment for osteoblasts or osteoprogenitor cells. The purpose of this study is to obtain bone-like apatite layer onto chitosan fiber mesh tissue engineering scaffolds, by means of using a simple biomimetic coating process and to determine the influence of this coating on osteoblastic cell responses. Chitosan fiber mesh scaffolds produced by a previously described wet spinning methodology were initially wet with a Bioglass"–water suspension by means of a spraying methodology and then immersed in a simulated body fluid (SBF) mimicking physiological conditions for one week. The formation of apatite layer was observed morphologically by scanning electron microscopy (SEM). As a result of the use of the novel spraying methodology, a fine coating could also be observed penetrating into the pores, that is clearly within the bulk of the scaffolds. Fourier Transform Infrared spectroscopy (FTIRATR), Electron Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) analysis also confirmed the presence of apatite-like layer. A human osteoblast-like cell line (SaOs-2) was used for the direct cell contact assays. After 2 weeks of culture, samples were observed under the SEM. When compared to the control samples (unmodified chitosan fiber mesh scaffolds) the cell population was found to be higher in the Ca–P biomimetic coated scaffolds, which indicates that the levels of cell proliferation on this kind of scaffolds could be enhanced. Furthermore, it was also observed that the cells seeded in the Ca–P coated scaffolds have a more spread and flat morphology, which reveals an improvement on the cell adhesion patterns, phenomena that are always important in processes such as osteoconduction