Trophic Ecology of Atlantic Bluefin Tuna (Thunnus thynnus) Larvae from the Gulf of Mexico and NW Mediterranean Spawning Grounds: A Comparative Stable Isotope Study

The present study uses stable isotopes of nitrogen and carbon (δ15Nandδ13C) as trophic indicators for Atlantic bluefin tuna larvae (BFT) (6–10mm standard length) in the highly contrasting environmental conditions of the Gulf of Mexico (GOM) and the Balearic Sea (MED). These regions are differentiated by their temperature regime and relative productivity, with the GOM being significantly warmer and more productive. MED BFT larvae showed the highest δ15N signatures, implying an elevated trophic position above the underlyingmicrozooplankton baseline. Ontogenetic dietary shifts were observed in the BFT larvae from the GOM and MED which indicates early life trophodynamics differences between these spawning habitats. Significant trophic differences between the GOM and MED larvae were observed in relation to δ15N signatures in favour of the MED larvae, which may have important implications in their growth during their early life stages. These low δ15N levels in the zooplankton from the GOM may be an indication of a shifting isotopic baseline in pelagic food webs due to diatrophic inputs by cyanobacteria. Lack of enrichment for δ15N in BFT larvae compared to zooplankton implies an alternative grazing pathway from the traditional food chain of phytoplankton— zooplankton—larval fish. Results provide insight for a comparative characterization of the trophic pathways variability of the two main spawning grounds for BFT larvaeVersión del editor4,411

Enterohemorrhagic E. coli Requires N-WASP for Efficient Type III Translocation but Not for EspFU-Mediated Actin Pedestal Formation

Upon infection of mammalian cells, enterohemorrhagic E. coli (EHEC) O157:H7 utilizes a type III secretion system to translocate the effectors Tir and EspFU (aka TccP) that trigger the formation of F-actin-rich ‘pedestals’ beneath bound bacteria. EspFU is localized to the plasma membrane by Tir and binds the nucleation-promoting factor N-WASP, which in turn activates the Arp2/3 actin assembly complex. Although N-WASP has been shown to be required for EHEC pedestal formation, the precise steps in the process that it influences have not been determined. We found that N-WASP and actin assembly promote EHEC-mediated translocation of Tir and EspFU into mammalian host cells. When we utilized the related pathogen enteropathogenic E. coli to enhance type III translocation of EHEC Tir and EspFU, we found surprisingly that actin pedestals were generated on N-WASP-deficient cells. Similar to pedestal formation on wild type cells, Tir and EspFU were the only bacterial effectors required for pedestal formation, and the EspFU sequences required to interact with N-WASP were found to also be essential to stimulate this alternate actin assembly pathway. In the absence of N-WASP, the Arp2/3 complex was both recruited to sites of bacterial attachment and required for actin assembly. Our results indicate that actin assembly facilitates type III translocation, and reveal that EspFU, presumably by recruiting an alternate host factor that can signal to the Arp2/3 complex, exhibits remarkable versatility in its strategies for stimulating actin polymerization

The EHEC Type III Effector NleL Is an E3 Ubiquitin Ligase That Modulates Pedestal Formation

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 causes hemorrhagic colitis and may result in potentially fatal hemolytic uremia syndrome in humans. EHEC colonize the intestinal mucosa and promote the formation of actin-rich pedestals via translocated type III effectors. Two EHEC type III secreted effectors, Tir and EspFu/TccP, are key players for pedestal formation. We discovered that an EHEC effector protein called Non-LEE-encoded Ligase (NleL) is an E3 ubiquitin ligase. In vitro, we showed that the NleL C753 residue is critical for its E3 ligase activity. Functionally, we demonstrated that NleL E3 ubiquitin ligase activity is involved in modulating Tir-mediated pedestal formation. Surprisingly, EHEC mutant strain deficient in the E3 ligase activity induced more pedestals than the wild-type strain. The canonical EPEC strain E2348/69 normally lacks the nleL gene, and the ectopic expression of the wild-type EHEC nleL, but not the catalytically-deficient nleL(C753A) mutant, in this strain resulted in fewer actin-rich pedestals. Furthermore, we showed that the C. rodentium NleL homolog is a E3 ubiquitin ligase and is required for efficient infection of murine colonic epithelial cells in vivo. In summary, our study demonstrated that EHEC utilizes NleL E3 ubiquitin ligase activity to modulate Tir-mediated pedestal formation.National Institutes of Health (U.S.) (grant AI078092)National Institutes of Health (U.S.) (grant AI068655

Iron Behaving Badly: Inappropriate Iron Chelation as a Major Contributor to the Aetiology of Vascular and Other Progressive Inflammatory and Degenerative Diseases

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular "reactive oxygen species" (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation. We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation). The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible. This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, etc...Comment: 159 pages, including 9 Figs and 2184 reference

Flexible Terahertz Metamaterials for Frequency Selective Surfaces

While recent years have seen great advances in the generation, detection, and application of terahertz frequency radiation, this region of the electromagnetic spectrum still suffers from a lack of efficient and effective frequency specific optical components. While such terahertz devices do exist, they are often limited by the materials they are based on and a lack of frequency selectivity and tunability. Metamaterial devices can provide frequency resonant behavior in the form of transmissive and reflective filters. Such a frequency selective surface can also be made tunable via the use of a flexible substrate. In this talk, we will highlight work involving the design, fabrication, and characterization of terahertz metamaterial devices based on flexible substrates. Finite element method simulations have been utilized to design a split-ring resonator (SRR) structure on a flexible SU8 polymer substrate with a targeted 250 GHz resonant response. Multiple configurations of SRR arrays have been fabricated on free standing SU8 substrates. These devices have subsequently been characterized using terahertz time-domain spectroscopy and imaging systems. The metamaterial devices have shown selective transmission and reflection over a narrow range of frequencies near the targeted resonance at 250 GHz. Details of both the design, fabrication, and characterization will be discussed

Flexible Terahertz Metamaterials for Frequency Selective Surfaces

While recent years have seen great advances in the generation, detection, and application of terahertz frequency radiation, this region of the electromagnetic spectrum still suffers from a lack of efficient and effective frequency specific optical components. While such terahertz devices do exist, they are often limited by the materials they are based on and a lack of frequency selectivity and tunability. Metamaterial devices can provide frequency resonant behavior in the form of transmissive and reflective filters. Such a frequency selective surface can also be made tunable via the use of a flexible substrate. In this talk, we will highlight work involving the design, fabrication, and characterization of terahertz metamaterial devices based on flexible substrates. Finite element method simulations have been utilized to design a split-ring resonator (SRR) structure on a flexible SU8 polymer substrate with a targeted 250 GHz resonant response. Multiple configurations of SRR arrays have been fabricated on free standing SU8 substrates. These devices have subsequently been characterized using terahertz time-domain spectroscopy and imaging systems. The metamaterial devices have shown selective transmission and reflection over a narrow range of frequencies near the targeted resonance at 250 GHz. Details of both the design, fabrication, and characterization will be discussed

Bending Induced Tuning of the Resonant Response of a Flexible THz Metamaterial Device

The effects of bending a 2-dimensional planar array of rectangular split-ring resonators (SRRs) is observed by mounting the array to varying diameter HDPE cylinders. By studying the transmission of pulsed THz light through the SRR-cylinder system, it shown that the resonant frequency and response of the arrays are tunable as a function of the radius of curvature

Bending Induced Tuning of the Resonant Response of a Flexible THz Metamaterial Device

The effects of bending a 2-dimensional planar array of rectangular split-ring resonators (SRRs) is observed by mounting the array to varying diameter HDPE cylinders. By studying the transmission of pulsed THz light through the SRR-cylinder system, it shown that the resonant frequency and response of the arrays are tunable as a function of the radius of curvature