615 research outputs found
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 6âh over a 2-day period using net traps deployed at 150âm 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
Phospholipid synthesis rates in the eastern subtropical South Pacific Ocean
Membrane lipid molecules are a major component of planktonic organisms and this is particularly true of the microbial picoplankton that dominate the open ocean; with their high surface-area to volume ratios, the synthesis of membrane lipids places a major demand on their overall cell metabolism. Specifically, the synthesis of cell membrane phospholipids creates a demand for the nutrient phosphorus, and we sought to refine our understanding of the role of phospholipids in the upper ocean phosphorus cycle. We measured the rates of phospholipid synthesis in a transect of the eastern subtropical South Pacific from Easter Island to Concepcion, Chile as part of the BIOSOPE program. Our approach combined standard phosphorus radiotracer incubations and lipid extraction methods. We found that phospholipid synthesis rates varied from less than 1 to greater than 200 pmol P Lâ1 hâ1, and that phospholipid synthesis contributed between less than 5% to greater than 22% of the total PO43â incorporation rate. Changes in the percentage that phospholipid synthesis contributed to total PO43â uptake were strongly correlated with the ratio of primary production to bacterial production, which supported our hypothesis that heterotrophic bacteria were the primary agents of phospholipid synthesis. The spatial variation in phospholipid synthesis rates underscored the importance of heterotrophic bacteria in the phosphorus cycle of the eastern subtropical South Pacific, particularly the hyperoligotrophic South Pacific subtropical gyre
Sinking phytoplankton associated with carbon flux in the Atlantic Ocean
© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Limnology and Oceanography 61 (2016): 1172â1187, doi:10.1002/lno.10253.The composition of sinking particles and the mechanisms leading to their transport ultimately control how much carbon is naturally sequestered in the deep ocean by the âbiological pump.â While detrital particles often contain much of the sinking carbon, sinking of intact phytoplankton cells can also contribute to carbon export, which represents a direct flux of carbon from the atmosphere to the deep ocean by circumventing the surface ocean food web. Phytoplankton that contributed to carbon flux were identified in sinking material collected by short-term sediment trap deployments conducted along a transect off the eastern shore of South America. Particulate organic carbon flux at 125 m depth did not change significantly along the transect. Instead, changes occurred in the composition and association of phytoplankton with detrital particles. The fluxes of diatoms, coccolithophores, dinoflagellates, and nano-sized cells at 125 m were unrelated to the overlying surface population abundances, indicating that functional-group specific transport mechanisms were variable across locations. The dominant export mechanism of phytoplankton at each station was putatively identified by principal component analysis and fell into one of three categories; (1) transport and sinking of individual, viable diatom cells, (2) transport by aggregates and fecal pellets, or (3) enhanced export of coccolithophores through direct settling and/or aggregationFunding for the DeepDOM cruise was
provided by the National Science Foundation (NSF) grant OCE-1154320
to E. B. Kujawinski and K. Longnecker, WHOI. Partial research support
was provided by NSF through grants OCE-0925284, and OCE-1316036
to S.T. Dyhrman. C.A. Durkin was supported by a Woods Hole Oceanographic
Institution Devonshire Postdoctoral Scholarship
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 (ÎŒ) is of great scientific interest. Many methods have been developed in order to assess bacterial or phytoplankton ÎŒ. One widely used method is to estimate ÎŒ 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 ÎŒ is simply to divide the production rate by the biomass or cell abundance estimate. Most methods using this approach to estimate ÎŒ are based on carbon (C) incorporation rates and C biomass measurements. Nevertheless it is also possible to estimate ÎŒ 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 ÎŒ. Contrary to other methods using C, this estimator does not need conversion factors and provides an evaluation of ÎŒ for both autotrophic and heterotrophic organisms. We report values of P-based ÎŒ in three size fractions (0.2â0.6; 0.6â2 and >2 ÎŒm) along a Southeast Pacific transect, over a wide range of P-replete trophic status. P-based ÎŒ values were higher in the 0.6â2 ÎŒm fraction than in the >2 ÎŒm 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 ÎŒm cells in this particular high-nutrient, low-light environment. P-based ÎŒ attributed to free-living bacteria (0.2-0.6 ÎŒm) and picoplankton (0.6â2 ÎŒm) size-fractions were relatively low (0.11±0.07 dâ1 and 0.14±0.04 dâ1, 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
lâUnivers (INSU), the Centre National dâEtudes 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
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
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