scholarly journals Phosphorus Scavenging in the Unicellular Marine Diazotroph Crocosphaera watsonii

2006 ◽  
Vol 72 (2) ◽  
pp. 1452-1458 ◽  
Author(s):  
Sonya T. Dyhrman ◽  
Sheean T. Haley
Keyword(s):  
Nitrogen Fixation ◽  
Critical Role ◽  
Sole Source ◽  
Phosphate Transport ◽  
Phosphate Binding ◽  
High Affinity ◽  
Tropical Environments ◽  
The Pacific ◽  
The Many ◽  
Crocosphaera Watsonii

ABSTRACT Through the fixation of atmospheric nitrogen and photosynthesis, marine diazotrophs play a critical role in the global cycling of nitrogen and carbon. Crocosphaera watsonii is a recently described unicellular diazotroph that may significantly contribute to marine nitrogen fixation in tropical environments. One of the many factors that can constrain the growth and nitrogen fixation rates of marine diazotrophs is phosphorus bioavailability. Using genomic and physiological approaches, we examined phosphorus scavenging mechanisms in strains of C. watsonii from both the Atlantic and the Pacific. Observations from the C. watsonii WH8501 genome suggest that this organism has the capacity for high-affinity phosphate transport (e.g., homologs of pstSCAB) in low-phosphate, oligotrophic systems. The pstS gene (high-affinity phosphate binding) is present in strains isolated from both the Atlantic and the Pacific, and its expression was regulated by the exogenous phosphate supply in strain WH8501. Genomic observation also indicated a broad capacity for phosphomonoester hydrolysis (e.g., a putative alkaline phosphatase). In contrast, no clear homologs of genes for phosphonate transport and hydrolysis could be identified. Consistent with these genomic observations, C. watsonii WH8501 is able to grow on phosphomonoesters as a sole source of added phosphorus but not on the phosphonates tested to date. Taken together these data suggest that C. watsonii has a robust capacity for scavenging phosphorus in oligotrophic systems, although this capacity differs from that of other marine cyanobacterial genera, such as Synechococcus, Prochlorococcus, and Trichodesmium.

scholarly journals The high-affinity phosphate-binding protein PstS is accumulated under high fructose concentrations and mutation of the corresponding gene affects differentiation in Streptomyces lividans

Microbiology ◽  
2005 ◽  
Vol 151 (8) ◽  
pp. 2583-2592 ◽  
Author(s):  
Margarita Díaz ◽  
Ana Esteban ◽  
José Manuel Fernández-Abalos ◽  
Ramón I. Santamaría
Keyword(s):  
Culture Media ◽  
Binding Protein ◽  
Protein Pattern ◽  
Phosphate Transport ◽  
Streptomyces Lividans ◽  
Null Mutant ◽  
Phosphate Binding ◽  
Genetic Switch ◽  
High Affinity ◽  
Phosphate Binding Protein

The secreted protein pattern of Streptomyces lividans depends on the carbon source present in the culture media. One protein that shows the most dramatic change is the high-affinity phosphate-binding protein PstS, which is strongly accumulated in the supernatant of liquid cultures containing high concentrations (>3 %) of certain sugars, such as fructose, galactose and mannose. The promoter region of this gene and that of its Streptomyces coelicolor homologue were used to drive the expression of a xylanase in S. lividans that was accumulated in the culture supernatant when grown in the presence of fructose. PstS accumulation was dramatically increased in a S. lividans polyphosphate kinase null mutant (Δppk) and was impaired in a deletion mutant lacking phoP, the transcriptional regulator gene of the two-component phoR-phoP system that controls the Pho regulon. Deletion of the pstS genes in S. lividans and S. coelicolor impaired phosphate transport and accelerated differentiation and sporulation on solid media. Complementation with a single copy in a S. lividans pstS null mutant returned phosphate transport and sporulation to levels similar to those of the wild-type strain. The present work demonstrates that carbon and phosphate metabolism are linked in the regulation of genes and that this can trigger the genetic switch towards morphogenesis.

scholarly journals Molecular Mechanisms of Phosphate Sensing, Transport and Signalling in Streptomyces and Related Actinobacteria

2021 ◽  
Vol 22 (3) ◽  
pp. 1129
Author(s):  
Juan Francisco Martín ◽  
Paloma Liras
Keyword(s):  
Transport System ◽  
Inorganic Phosphate ◽  
Molecular Mechanisms ◽  
Phosphate Transport ◽  
Transport Systems ◽  
Outer Side ◽  
Phosphate Binding ◽  
Streptomyces Species ◽  
High Affinity ◽  
Sugar Phosphates

Phosphorous, in the form of phosphate, is a key element in the nutrition of all living beings. In nature, it is present in the form of phosphate salts, organophosphates, and phosphonates. Bacteria transport inorganic phosphate by the high affinity phosphate transport system PstSCAB, and the low affinity PitH transporters. The PstSCAB system consists of four components. PstS is the phosphate binding protein and discriminates between arsenate and phosphate. In the Streptomyces species, the PstS protein, attached to the outer side of the cell membrane, is glycosylated and released as a soluble protein that lacks its phosphate binding ability. Transport of phosphate by the PstSCAB system is drastically regulated by the inorganic phosphate concentration and mediated by binding of phosphorylated PhoP to the promoter of the PstSCAB operon. In Mycobacterium smegmatis, an additional high affinity transport system, PhnCDE, is also under PhoP regulation. Additionally, Streptomyces have a duplicated low affinity phosphate transport system encoded by the pitH1–pitH2 genes. In this system phosphate is transported as a metal-phosphate complex in simport with protons. Expression of pitH2, but not that of pitH1 in Streptomyces coelicolor, is regulated by PhoP. Interestingly, in many Streptomyces species, three gene clusters pitH1–pstSCAB–ppk (for a polyphosphate kinase), are linked in a supercluster formed by nine genes related to phosphate metabolism. Glycerol-3-phosphate may be transported by the actinobacteria Corynebacterium glutamicum that contains a ugp gene cluster for glycerol-3-P uptake, but the ugp cluster is not present in Streptomyces genomes. Sugar phosphates and nucleotides are used as phosphate source by the Streptomyces species, but there is no evidence of the uhp gene involved in the transport of sugar phosphates. Sugar phosphates and nucleotides are dephosphorylated by extracellular phosphatases and nucleotidases. An isolated uhpT gene for a hexose phosphate antiporter is present in several pathogenic corynebacteria, such as Corynebacterium diphtheriae, but not in non-pathogenic ones. Phosphonates are molecules that contains phosphate linked covalently to a carbon atom through a very stable C–P bond. Their utilization requires the phnCDE genes for phosphonates/phosphate transport and genes for degradation, including those for the subunits of the C–P lyase. Strains of the Arthrobacter and Streptomyces genera were reported to degrade simple phosphonates, but bioinformatic analysis reveals that whole sets of genes for putative phosphonate degradation are present only in three Arthrobacter species and a few Streptomyces species. Genes encoding the C–P lyase subunits occur in several Streptomyces species associated with plant roots or with mangroves, but not in the laboratory model Streptomyces species; however, the phnCDE genes that encode phosphonates/phosphate transport systems are frequent in Streptomyces species, suggesting that these genes, in the absence of C–P lyase genes, might be used as surrogate phosphate transporters. In summary, Streptomyces and related actinobacteria seem to be less versatile in phosphate transport systems than Enterobacteria.

scholarly journals Radiation Necrosis of the Lateral Skull Base and Temporal Bone

2020 ◽  
Vol 34 (04) ◽  
pp. 265-271
Author(s):  
Marc W. Herr ◽  
Aurora G. Vincent ◽  
Meghan A. Skotnicki ◽  
Yadranko Ducic ◽  
Spiros Manolidis
Keyword(s):  
Radiation Therapy ◽  
Temporal Bone ◽  
Radiation Necrosis ◽  
Critical Role ◽  
Therapeutic Effects ◽  
Normal Tissues ◽  
Lateral Skull Base ◽  
The Many ◽  
Work Up

AbstractRadiation therapy plays a critical role in the treatment of malignancies involving the head and neck. Although the therapeutic effects of ionizing radiation are achieved, normal tissues are also susceptible to injury and significant long-term sequelae. Osteoradionecrosis of the temporal bone (ORNTB) is among the many complications that can arise after therapy. ORNTB is a debilitating and potentially lethal condition that continues to challenge patients and treating physicians. Herein, we review the pathophysiology, presentation, work-up, and management of ORNTB.

scholarly journals Suppression of autocrine and paracrine functions of basic fibroblast growth factor by stable expression of perlecan antisense cDNA.

1997 ◽  
Vol 17 (4) ◽  
pp. 1938-1946 ◽  
Author(s):  
D Aviezer ◽  
R V Iozzo ◽  
D M Noonan ◽  
A Yayon
Keyword(s):  
Growth Factor ◽  
Fibroblast Growth Factor ◽  
Core Protein ◽  
Critical Role ◽  
Receptor Activation ◽  
Fibroblast Growth ◽  
Proliferating Cells ◽  
Transfected Cells ◽  
High Affinity

Heparan sulfate proteoglycans (HSPG) play a critical role in the formation of distinct fibroblast growth factor (FGF)-HS complexes, augmenting high-affinity binding and receptor activation. Perlecan, a secreted HSPG abundant in proliferating cells, is capable of inducing FGF-receptor interactions in vitro and angiogenesis in vivo. Stable and specific reduction of perlecan levels in mouse NIH 3T3 fibroblasts and human metastatic melanoma cells has been achieved by expression of antisense cDNA corresponding to the N-terminal and HS attachment domains of perlecan. Long-term perlecan downregulation is evidenced by reduced levels of perlecan mRNA and core protein as indicated by Northern blot analysis, immunoblots, and immunohistochemistry, using DNA probes and antibodies specific to mouse or human perlecan. The response of antisense perlecan-expressing cells to increasing concentrations of basic FGF (bFGF) is dramatically reduced in comparison to that in wild-type or vector-transfected cells, as measured by thymidine incorporation and rate of proliferation. Furthermore, receptor binding and affinity labeling of antisense perlecan-transfected cells with 125I-bFGF is markedly inhibited, indicating that eliminating perlecan expression results in reduced high-affinity bFGF binding. Both the binding and mitogenic response of antisense-perlecan-expressing clones to bFGF can be rescued by exogenous heparin or perlecan. These results support the notion that perlecan is a major accessory receptor for bFGF in mouse fibroblasts and human melanomas and point to the possible use of perlecan antisense constructs as specific modulators of bFGF-mediated responses.

scholarly journals Non-Hermitian physics for optical manipulation uncovers inherent instability of large clusters

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiao Li ◽  
Yineng Liu ◽  
Zhifang Lin ◽  
Jack Ng ◽  
C. T. Chan
Keyword(s):  
Large Scale ◽  
Critical Role ◽  
Optical Forces ◽  
Exceptional Points ◽  
Complex Eigenvalues ◽  
Microscopic World ◽  
The Stability ◽  
The Many ◽  
Large Clusters ◽  
Conventional Systems

AbstractIntense light traps and binds small particles, offering unique control to the microscopic world. With incoming illumination and radiative losses, optical forces are inherently nonconservative, thus non-Hermitian. Contrary to conventional systems, the operator governing time evolution is real and asymmetric (i.e., non-Hermitian), which inevitably yield complex eigenvalues when driven beyond the exceptional points, where light pumps in energy that eventually “melts” the light-bound structures. Surprisingly, unstable complex eigenvalues are prevalent for clusters with ~10 or more particles, and in the many-particle limit, their presence is inevitable. As such, optical forces alone fail to bind a large cluster. Our conclusion does not contradict with the observation of large optically-bound cluster in a fluid, where the ambient damping can take away the excess energy and restore the stability. The non-Hermitian theory overturns the understanding of optical trapping and binding, and unveils the critical role played by non-Hermiticity and exceptional points, paving the way for large-scale manipulation.

scholarly journals Preliminary time-of-flight neutron diffraction studies ofEscherichia coliABC transport receptor phosphate-binding protein at the Protein Crystallography Station

2014 ◽  
Vol 70 (6) ◽  
pp. 819-822 ◽  
Author(s):  
K. H. Sippel ◽  
J. Bacik ◽  
F. A. Quiocho ◽  
S. Z. Fisher
Keyword(s):  
Neutron Diffraction ◽  
Binding Protein ◽  
Protein Crystallography ◽  
Phosphate Transport ◽  
Phosphate Binding ◽  
Science Center ◽  
Data Set ◽  
Acceptor Group ◽  
Phosphate Binding Protein ◽  
Ph Range

Inorganic phosphate is an essential molecule for all known life. Organisms have developed many mechanisms to ensure an adequate supply, even in low-phosphate conditions. In prokaryotes phosphate transport is instigated by the phosphate-binding protein (PBP), the initial receptor for the ATP-binding cassette (ABC) phosphate transporter. In the crystal structure of the PBP–phosphate complex, the phosphate is completely desolvated and sequestered in a deep cleft and is bound by 13 hydrogen bonds: 12 to protein NH and OH donor groups and one to a carboxylate acceptor group. The carboxylate plays a key recognition role by accepting a phosphate hydrogen. PBP phosphate affinity is relatively consistent across a broad pH range, indicating the capacity to bind monobasic (H2PO4−) and dibasic (HPO42−) phosphate; however, the mechanism by which it might accommodate the second hydrogen of monobasic phosphate is unclear. To answer this question, neutron diffraction studies were initiated. Large single crystals with a volume of 8 mm3were grown and subjected to hydrogen/deuterium exchange. A 2.5 Å resolution data set was collected on the Protein Crystallography Station at the Los Alamos Neutron Science Center. Initial refinement of the neutron data shows significant nuclear density, and refinement is ongoing. This is the first report of a neutron study from this superfamily.

Burden-sharing: the US, Australia and New Zealand alliances in the Pacific islands

2021 ◽  
Author(s):  
Joanne Wallis ◽  
Anna Powles
Keyword(s):  
United States ◽  
New Zealand ◽  
Pacific Islands ◽  
Critical Role ◽  
The United States ◽  
Burden Sharing ◽  
Military Capability ◽  
The Pacific ◽  
Security Challenges ◽  
The Us

Abstract One of President Joseph Biden's foreign policy priorities is to ‘renew’ and ‘strengthen’ the United States' alliances, as they were perceived to have been ‘undermined’ during the Trump administration, which regularly expressed concern that allies were free-riding on the United States' military capability. Yet the broad range of threats states face in the contemporary context suggests that security assistance from allies no longer only—or even primarily—comes in the form of military capability. We consider whether there is a need to rethink understandings of how alliance relationships are managed, particularly how the goals—or strategic burdens—of alliances are understood, how allies contribute to those burdens, and how influence is exercised within alliances. We do this by analysing how the United States–Australia and Australia–New Zealand alliances operate in the Pacific islands. Our focus on the Pacific islands reflects the United States' perception that the region plays a ‘critical’ role in helping to ‘preserve a free and open Indo-Pacific region’. We conclude that these understandings need to be rethought, particularly in the Pacific islands, where meeting non-traditional security challenges such as economic, social and environmental issues, is important to advancing the United States, Australia and New Zealand's shared strategic goal of remaining the region's primary security partners and ensuring that no power hostile to their interests establishes a strategic foothold.

Active GPIIb-IIIa conformations that link ligand interaction with cytoskeletal reorganization

Blood ◽  
2000 ◽  
Vol 96 (7) ◽  
pp. 2487-2495 ◽  
Author(s):  
Traci Heath Mondoro ◽  
Melanie McCabe White ◽  
Lisa K. Jennings
Keyword(s):  
Platelet Aggregation ◽  
Ligand Binding ◽  
Critical Role ◽  
Adenosine Diphosphate ◽  
Full Scale ◽  
Cytoskeletal Reorganization ◽  
Clot Retraction ◽  
Ligand Interaction ◽  
High Affinity ◽  
Combination Treatments

Abstract Glycoprotein (GP) IIb-IIIa plays a critical role in platelet aggregation and platelet-mediated clot retraction. This study examined the intramolecular relationship between GPIIb-IIIa activation and fibrinogen binding, platelet aggregation, and platelet-mediated clot retraction. To distinguish between different high-affinity activation states of GPIIb-IIIa, the properties of an antibody (D3) specific for GPIIIa that induces GPIIb-IIIa binding to adhesive protein molecules and yet completely inhibits clot retraction were used. Clot retraction inhibition by D3 was not due to altered platelet-fibrin interaction; however, combination treatments of D3 and adenosine diphosphate (ADP) inhibited full-scale aggregation and decreased the amounts of GPIIb-IIIa and talin incorporated into the core cytoskeletons. Morphologic evaluation of the D3/ADP aggregates showed platelets that were activated but to a lesser extent when compared to ADP only. ADP addition to platelets caused an increase in the number of D3 binding sites indicating that ligand had bound to the GPIIb-IIIa receptor. These data suggest that high-affinity GPIIb-IIIa– mediated ligand binding can be separated mechanistically from GPIIb-IIIa–mediated clot retraction and that clot retraction requires additional signaling through GPIIb-IIIa after ligand binding. The conformation recognized by D3 represents the expression of a GPIIb-IIIa activation state that participates in full-scale platelet aggregation, cytoskeletal reorganization, and clot retraction.

Part 1: Chapter 2 Outline History of Geological Research

1997 ◽  
Vol 17 (1) ◽  
pp. 16-22 ◽  
Author(s):  
W. Brian Harland
Keyword(s):  
Eighteenth Century ◽  
Know How ◽  
Hydrographic Survey ◽  
The Pacific ◽  
History Of ◽  
Arctic Exploration ◽  
The Many ◽  
Geological Work ◽  
Geological Research ◽  
Selection Of

Useful records of observations perhaps began in 1596 with Barents' voyage and resulting chart. The many expeditions until the middle of the eighteenth century were primarily for whaling with minor additions to the charts. In 1758 A. R. Martin led a Swedish voyage and in 1773 C. J. Phipps commanded a British naval expedition, the first of several, to seek a northeast passage to the Pacific. They penetrated no further than Spitsbergen and made useful observations. At that time and for many years the British Admiralty was concerned with extensive Arctic exploration. The elaborate nature of these expeditions was not so much designed for scientific purposes as for useful employment for enterprising officers, with ships in numbers no longer needed in the period of naval supremacy after 1805. Hydrographic survey was often the principal achievement. In terms of efficiency and Arctic know-how the early whalers such as Scoresby were superior.1827 may be considered as the year when geological work began, with expeditions from Norway (B. M. Keilhau 1831) and Britain (Capt. Parry, e.g. Horner 1860; Salter 1860). Keilhau, a geologist, visited Edgeoya and Bjornoya. Admiral Parry, Hydrographer of the Navy, wintered on HMS Hecla in Sorgfjorden where further specimens were collected. In 1837 an early Swedish expedition was directed by Loven. Then, 1838 to 1840, the French voyage of La Recherche took place under the Commission Scientifique du Nord (e.g. Robert 1840).Only a selection of the many expeditions in the second half of the century are noted here.

scholarly journals Role of Somatostatin in the Regulation of Central and Peripheral Factors of Satiety and Obesity

2020 ◽  
Vol 21 (7) ◽  
pp. 2568
Author(s):  
Ujendra Kumar ◽  
Sneha Singh
Keyword(s):  
Food Intake ◽  
Hormonal Regulation ◽  
Critical Role ◽  
Eating Behaviour ◽  
Peripheral Tissues ◽  
Complex Process ◽  
The Many ◽  
The One ◽  
Food Seeking

Obesity is one of the major social and health problems globally and often associated with various other pathological conditions. In addition to unregulated eating behaviour, circulating peptide-mediated hormonal secretion and signaling pathways play a critical role in food intake induced obesity. Amongst the many peptides involved in the regulation of food-seeking behaviour, somatostatin (SST) is the one which plays a determinant role in the complex process of appetite. SST is involved in the regulation of release and secretion of other peptides, neuronal integrity, and hormonal regulation. Based on past and recent studies, SST might serve as a bridge between central and peripheral tissues with a significant impact on obesity-associated with food intake behaviour and energy expenditure. Here, we present a comprehensive review describing the role of SST in the modulation of multiple central and peripheral signaling molecules. In addition, we highlight recent progress and contribution of SST and its receptors in food-seeking behaviour, obesity (orexigenic), and satiety (anorexigenic) associated pathways and mechanism.

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