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Diverse diazotrophs are present on sinking particles in the North Pacific Subtropical Gyre.
Sinking particles transport carbon and nutrients from the surface ocean into the deep sea and are considered hot spots for bacterial diversity and activity. In the oligotrophic oceans, nitrogen (N2)-fixing organisms (diazotrophs) are an important source of new N but the extent to which these organisms are present and exported on sinking particles is not well known. Sinking particles were collected every 6 h over a 2-day period using net traps deployed at 150 m in the North Pacific Subtropical Gyre. The bacterial community and composition of diazotrophs associated with individual and bulk sinking particles was assessed using 16S rRNA and nifH gene amplicon sequencing. The bacterial community composition in bulk particles remained remarkably consistent throughout time and space while large variations of individually picked particles were observed. This difference suggests that unique biogeochemical conditions within individual particles may offer distinct ecological niches for specialized bacterial taxa. Compared to surrounding seawater, particle samples were enriched in different size classes of globally significant N2-fixing cyanobacteria including Trichodesmium, symbionts of diatoms, and the unicellular cyanobacteria Crocosphaera and UCYN-A. The particles also contained nifH gene sequences of diverse non-cyanobacterial diazotrophs suggesting that particles could be loci for N2 fixation by heterotrophic bacteria. The results demonstrate that diverse diazotrophs were present on particles and that new N may thereby be directly exported from surface waters on sinking particles
Microbes and the marine phosphorus cycle
Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 2 (2007): 110-116.Phosphorus (P) is fundamental to life,
and years of study in marine systems
have built a broad understanding of
the marine P cycle. Various aspects of
marine P biogeochemistry have been
reviewed previously (Benitez-Nelson,
2000; Paytan and McLaughlin, 2007).
Here, we focus on recent advances in
our understanding of marine P and
the interactions between microbes and
the P cycle. These advances come from
a variety of disciplines, but generally
highlight three main themes: (1) ocean
microbes are adapted for surviving in a
variable P environment, (2) the dissolved
organic phosphorus (DOP) pool likely
plays a critical role in driving growth,
metabolism, and community composition
of ocean microorganisms, and
(3) P is very rapidly cycled, which highlights
its importance in marine systems
Growth and specific P-uptake rates of bacterial and phytoplanktonic communities in the Southeast Pacific (BIOSOPE cruise)
© 2007 Author(s) et al. This is an open-access article distributed under the terms of a Creative Commons License. The definitive version was published in Biogeosciences 4 (2007): 941-956, doi:10.5194/bg-4-941-2007Predicting heterotrophic bacteria and phytoplankton specific growth rates (μ) is of great scientific interest. Many methods have been developed in order to assess bacterial or phytoplankton μ. One widely used method is to estimate μ from data obtained on biomass or cell abundance and rates of biomass or cell production. According to Kirchman (2002), the most appropriate approach for estimating μ is simply to divide the production rate by the biomass or cell abundance estimate. Most methods using this approach to estimate μ are based on carbon (C) incorporation rates and C biomass measurements. Nevertheless it is also possible to estimate μ using phosphate (P) data. We showed that particulate phosphate (PartP) can be used to estimate biomass and that the P uptake rate to PartP ratio can be employed to assess μ. Contrary to other methods using C, this estimator does not need conversion factors and provides an evaluation of μ for both autotrophic and heterotrophic organisms. We report values of P-based μ in three size fractions (0.2–0.6; 0.6–2 and >2 μm) along a Southeast Pacific transect, over a wide range of P-replete trophic status. P-based μ values were higher in the 0.6–2 μm fraction than in the >2 μm fraction, suggesting that picoplankton-sized cells grew faster than the larger cells, whatever the trophic regime encountered. Picoplankton-sized cells grew significantly faster in the deep chlorophyll maximum layer than in the upper part of the photic zone in the oligotrophic gyre area, suggesting that picoplankton might outcompete >2 μm cells in this particular high-nutrient, low-light environment. P-based μ attributed to free-living bacteria (0.2-0.6 μm) and picoplankton (0.6–2 μm) size-fractions were relatively low (0.11±0.07 d−1 and 0.14±0.04 d−1, respectively) in the Southeast Pacific gyre, suggesting that the microbial community turns over very slowly.This research was funded by the Centre National de
la Recherche Scientifique (CNRS), the Institut des Sciences de
l’Univers (INSU), the Centre National d’Etudes Spatiales (CNES),
the European Space Agency (ESA), The National Aeronautics
and Space Administration (NASA) and the Natural Sciences and
Engineering Research Council of Canada (NSERC). This work is
funded in part by the French Research and Education council
Phosphate availability and the ultimate control of new nitrogen input by nitrogen fixation in the tropical Pacific Ocean
International audienceDue to the low atmospheric input of phosphate into the open ocean, it is one of the key nutrients that could ultimately control primary production and carbon export into the deep ocean. The observed trend over the last 20 years has shown a decrease in the dissolved inorganic phosphate (DIP) pool in the North Pacific gyre, which has been correlated to the increase in di-nitrogen (N2) fixation rates. Following a NW-SE transect, in the Southeast Pacific during the early austral summer (BIOSOPE cruise), we present data on DIP, dissolved organic phosphate (DOP) and particulate phosphate (PP) pools along with DIP turnover times (TDIP) and N2 fixation rates. We observed a decrease in DIP concentration from the edges to the centre of the gyre. Nevertheless the DIP concentrations remained above 100 nmol L-1 and T DIP was more than 6 months in the centre of the gyre; DIP availability remained largely above the level required for phosphate limitation to occur and the absence of Trichodesmium spp and low nitrogen fixation rates were likely to be controlled by other factors such as temperature or iron availability. This contrasts with recent observations in the North Pacific Ocean at the ALOHA station and in the western Pacific Ocean at the same latitude (DIAPALIS cruises) where lower DIP concentrations (-1) and T DIP 2 fixation rates and possibly carbon dioxide sequestration, if the primary ecophysiological controls, temperature and/or iron availability, were alleviated
Somatostatin receptor 2A expression in choroidal neovascularization secondary to age-related macular degeneration
PURPOSE: The growth of ocular neovascularization is regulated by a balance
between stimulating and inhibiting growth factors. Somatostatin affects
angiogenesis by inhibiting the growth hormone-insulin-like growth factor
axis and also has a direct antiproliferative effect on human retinal
endothelial cells. The purpose of our study is to investigate the
expression of somatostatin receptor (sst) subtypes and particularly sst
subtype 2A (sst2A) in normal human macula, and to study sst2A in different
stages of age-related maculopathy (ARM), because of the potential
anti-angiogenic effect of somatostatin analogues. METHODS: Sixteen eyes
(10 enucleated eyes, 4 donor eyes, and 2 surgically removed choroidal
neovascular [CNV] membranes) of 15 patients with eyes at different stages
of ARM were used for immunohistochemistry. Formaldehyde-fixed
paraffin-embedded slides were incubated with a polyclonal anti-human sst2A
antibody. mRNA expression of five ssts and somatostatin was determined in
the posterior pole of three normal human eyes by reverse
transcriptase-polymerase chain reaction. RESULTS: The immunohistochemical
expression of sstA in newly formed endothelial cells and fibroblast-like
cells was strong in fibrovascular CNV membranes. mRNA of sst subtypes 1,
2A, and 3, as well as somatostatin, was present in the normal posterior
pole; sst subtypes 4 and 5 were not detectable. CONCLUSIONS: Most
early-formed CNV in ARM express sst2A. The presence of mRNA of sst subtype
2A was observed in normal human macula, and subtypes 1 and 3 and
somatostatin are also present. sst2A receptors bind potential
anti-angiogenic somatostatin analogues such as octreotide. Therefore,
somatostatin analogues may be an effective therapy in early stages of CNV
in ARM
Resource allocation by the marine cyanobacterium Synechococcus WH8102 in response to different nutrient supply ratios
Differences in relative availability of nitrate vs. phosphate may contribute to regional variations in plankton elemental stoichiometry. As a representative of the globally abundant marine Synechococcus, strain WH8102 was grown in 16 chemostats up to 52  d at a fixed growth rate with nitrogen–phosphorus ratios (N : Psupply) of 1–50. Initially, the phosphate and nitrate concentrations in the vessel decreased when the respective nutrient was limiting. Cell growth generally stabilized, although several chemostats had apparent oscillations in biomass. We observed extensive plasticity in the elemental content and ratios. N : Pcell matched the supply values between N : Psupply 5 and 20. The C : Pcell followed a similar trend. In contrast, the mean C : Ncell was 6.8 and did not vary as a function of supply ratios. We also observed that induction of alkaline phosphatase, the fraction of P allocated to nucleic acids, and the lipid sulfoquinovosyldiacylglycerol : phosphatidyglycerol ratio inversely correlated with P availability. Our results suggest that this extensive plasticity in the elemental content and ratios depends both on the external nutrient availability as well as past growth history. Thus, our study provides a quantitative understanding of the regulation of the elemental stoichiometry of an abundant ocean phytoplankton lineage
Adhesion molecules in iris biopsy specimens from patients with uveitis
BACKGROUND/AIMS: Earlier studies on intraocular tissue have demonstrated
that T lymphocytes play a major role in the pathogenesis of uveitis.
Adhesion molecules are immunoregulatory molecules for the interaction
between T lymphocytes and vascular endothelium and they play an important
role in the recruitment of specific T lymphocytes from the circulation
into inflamed tissue. In uveitis an increased expression of some of these
adhesion molecules may be expected. METHODS: The presence of adhesion
molecules was investigated in iris biopsy specimens from 11 patients with
uveitis and eight controls (patients with primary open angle glaucoma)
immunohistochemically with a panel of monoclonal antibodies: LECAM (CD
62L), ICAM-1 (CD 54), LFA-1 (CD 11a/18), VCAM-1 (CD 106), VLA-4 (CD 49d),
and HECA-452, a marker for high endothelial venules. RESULTS: Positive
staining for ICAM-1, LFA-1 and VCAM-1 was found in the iris in a
significantly higher number of uveitis patients than in controls. The
remaining adhesion molecules were also found in a higher number of uveitis
patients than in controls, but this difference did not reach statistical
significance. CONCLUSION: An increased expression of adhesion molecules
was found in the iris of patients with uveitis, indicating an
immunoregulatory function for adhesion molecules in the pathogenesis of
uveitis
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