Bacteria of the Thiomonas genus are ubiquitous in extreme environments, such as arsenic-rich acid mine drainage (AMD). The genome of one of these strains, Thiomonas sp. 3As, was sequenced, annotated, ...and examined, revealing specific adaptations allowing this bacterium to survive and grow in its highly toxic environment. In order to explore genomic diversity as well as genetic evolution in Thiomonas spp., a comparative genomic hybridization (CGH) approach was used on eight different strains of the Thiomonas genus, including five strains of the same species. Our results suggest that the Thiomonas genome has evolved through the gain or loss of genomic islands and that this evolution is influenced by the specific environmental conditions in which the strains live.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We explore whether assumptions about dust grain shape affect resulting estimates of the composition and grain size distribution of the AU Microscopii (AU Mic) debris disk from scattered light data ...collected by Lomax et al. (2018). The near edge-on orientation of the AU Mic debris disk makes it ideal for studying the effect of the scattering phase function (SPF) on the measured flux ratios as a function of wavelength and projected distance. Previous efforts to model the AU Mic debris disk have invoked a variety of dust grain compositions and explored the effect of porosity, but did not undertake a systematic effort to explore a full range of size distributions and compositions to understand possible degeneracies in fitting the data. The degree to which modelling dust grains with more realistic shapes compounds these degeneracies has also not previously been explored. We find differences in the grain properties retrieved depending on the grain shape model used. We also present here our calculations of porous grains of size parameters x = 0.1 to 48 and complex refractive indices (m = n+ik) ranging from n = 1.1 to 2.43 and k = 0 to 1.0, covering multiple compositions at visible and near infrared wavelengths such as ice, silicates, amorphous carbon, and tholins.
Measurements of visible and near-infrared reflection (0.38-5 {\mu}m) and mid to far infrared emission (5-200 {\mu}m) from telescope and satellite remote sensing instruments make it possible to ...investigate the composition of planetary surfaces via electronic transitions and vibrational modes of chemical bonds. Red spectral slopes at visible and near infrared wavelengths and absorption features at 3.3 and 3.4 {\mu}m observed in circumstellar disks, the interstellar medium, and on the surfaces of solar-system bodies are interpreted to be due to the presence of organic material and other carbon compounds. Identifying the origin of these features requires measurements of the optical properties of a variety of relevant analog and planetary materials. Spectroscopic models of dust within circumstellar disks and the interstellar medium as well as planetary regoliths often incorporate just one such laboratory measurement despite the wide variation in absorption and extinction properties of organic and other carbon-bearing materials. Here we present laboratory measurements of transmission spectra in the 1.5-13 {\mu}m region and use these to derive real and imaginary indices of refraction for two samples: 1) an analog to meteoritic insoluble organic matter and 2) a powdered Allende meteorite sample. We also test our refractive index retrieval method on a previously published transmission spectrum of an Mg-rich olivine. We compare optical measurements of the insoluble organic-matter analog to those of other solar-system and extrasolar organic analogs, such as amorphous carbon and tholins, and find that the indices of refraction of the newly characterized material differ significantly from other carbonaceous samples.
The small class of known stars with unusually warm, dusty debris disks is a key sample to probe in order to understand cascade models and extreme collisions that likely lead to the final ...configurations of planetary systems. Because of its extreme dustiness and small radius, the disk of BD +20 307 has a short predicted collision time and is therefore an interesting target in which to look for changes in dust quantity and composition over time. To compare with previous ground and Spitzer Space Telescope data, SOFIA photometry and spectroscopy were obtained. The system's 8.8-12.5 \(\mu\)m infrared emission increased by \(10 \pm 2 \%\) over nine years between the SOFIA and earlier Spitzer measurements. In addition to an overall increase in infrared excess, there is a suggestion of a greater increase in flux at shorter wavelengths (less than 10.6 \(\mu\)m) compared to longer wavelengths (greater than 10.6 \(\mu\)m). Steady-state collisional cascade models cannot explain the increase in BD +20 307's disk flux over such short timescales. A catastrophic collision between planetary-scale bodies is still the most likely origin for the system's extreme dust; however, the cause for its recent variation requires further investigation.
The light scattered from dust grains in debris disks is typically modeled as compact spheres using Lorenz-Mie theory or as porous spheres by incorporating an effective medium theory. In this work we ...examine the effect of incorporating a more realistic particle morphology on estimated radiation-pressure blowout sizes. To calculate the scattering and absorption cross sections of irregularly shaped dust grains, we use the discrete dipole approximation. These cross sections are necessary to calculate the \(\beta\)-ratio, which determines whether dust grains can remain gravitationally bound to their star. We calculate blowout sizes for a range of stellar spectral types corresponding with stars known to host debris disks. As with compact spheres, more luminous stars blow out larger irregularly shaped dust grains. We also find that dust grain composition influences blowout size such that absorptive grains are more readily removed from the disk. Moreover, the difference between blowout sizes calculated assuming spherical particles versus particle morphologies more representative of real dust particles is compositionally dependent as well, with blowout size estimates diverging further for transparent grains. We find that the blowout sizes calculated have a strong dependence on the particle model used, with differences in the blowout size calculated being as large as an order of magnitude for particles of similar porosities.
A major action of the hormone insulin is to increase glucose uptake into muscle and adipose tissues. This occurs through the insulin-regulated translocation of the glucose transporter GLUT4 from ...intracellular deposits to the cell surface. The dysregulation of this process is a major facet of insulin-resistance and Type-2 diabetes. In the absence of insulin, GLUT4 is sequestered intracellularly in two interlinked pools. These pools are the endosomal recycling compartment and a specialised insulin-sensitive compartment. GLUT4 vesicles within the specialised insulin-sensitive compartment are termed GSVs. GSVs provide a readily available store of GLUT4 that can be rapidly mobilised to the cell surface in response to insulin stimulation. GLUT4 within the cell is continually recycled through multiple compartments, including the endosomal recycling compartment and GSVs. Perturbation of flux through any of these compartments disrupts GLUT4 traffic and thus disrupts the insulin-response. Consequently, understanding these trafficking steps is an important research goal. The formation of GSVs and their insulin-stimulated translocation to, and fusion with, the plasma membrane are examples of regulated and specific membrane trafficking events. As such these events require SNARE proteins. This study has examined the functions of each of the members of the post-Golgi vSNAREs that make up the VAMP subfamily in the trafficking of GLUT4 into the insulin-sensitive compartment, as well as examining the contribution each of these vSNAREs plays in the SNARE complex involved in the insulin-stimulated translocation of GLUT4 to the cell surface. GLUT4 traffics through the endosomal system and the trans Golgi network (TGN) en route into GSVs in a process known to involve the t-SNARE syntaxin 16. In order to dissect the roles VAMP proteins play in the intracellular recycling and trafficking of GLUT4, the interactions of VAMP proteins with syntaxin 16 and its regulatory Sec-1/Munc-18 protein, mVps45 have been examined. Further, the effects of depletion of these VAMPs in GLUT4 distribution has been examined in HeLa cells expressing HA-GLUT4-GFP as a surrogate for adipose and muscle tissue. The fusion of GLUT4-containing vesicles with the cell surface in response to insulin stimulation is a key component of the insulin-response. Although there is consensus that tSNAREs involved in this process are syntaxin 4 and SNAP23, there is discord in the literature regarding the role each vSNARE plays in this fusion event. Many studies support a role for VAMP2, however recently it has been suggested that VAMPs 3 and 8 may also be involved. The roles of these VAMPs, as well as the other post-Golgi vSNAREs expressed in adipocytes, in the fusion of GLUT4-containing vesicles with the cell surface have been examined. This has been achieved through the characterisation of the expression level, subcellular distribution of the VAMPs and determination of associations that take place between each VAMP protein and the tSNARE complex made up of syntaxin 4 and SNAP23. The results from these experiments show that despite all VAMPs being capable of forming SDS-resistant SNARE complexes with either syntaxin 4 and SNAP23 or syntaxin 16 and SNAP23, in the cellular environment only VAMP2 interacts with syntaxin 4 and only VAMP4 interacts with syntaxin 16. This, alongside the finding that each VAMP protein is expressed at varying levels and localises with different pools of GLUT4, suggests that VAMP2, not VAMPs 3 or 8, is the major vSNARE involved in the trafficking of GLUT4 to the cell surface. The finding that VAMP4 is the only VAMP that interacts with syntaxin 16, alongside the results of VAMP depletion in HeLa cells expressing HA-GLUT4-GFP, support the hypothesis that VAMP4 is involved in sorting GLUT4 out of the endosomal pool and into GSVs.
A major action of the hormone insulin is to increase glucose uptake into muscle and adipose tissues. This occurs through the insulin-regulated translocation of the glucose transporter GLUT4 from ...intracellular deposits to the cell surface. The dysregulation of this process is a major facet of insulin-resistance and Type-2 diabetes. In the absence of insulin, GLUT4 is sequestered intracellularly in two interlinked pools. These pools are the endosomal recycling compartment and a specialised insulin-sensitive compartment. GLUT4 vesicles within the specialised insulin-sensitive compartment are termed GSVs. GSVs provide a readily available store of GLUT4 that can be rapidly mobilised to the cell surface in response to insulin stimulation. GLUT4 within the cell is continually recycled through multiple compartments, including the endosomal recycling compartment and GSVs. Perturbation of flux through any of these compartments disrupts GLUT4 traffic and thus disrupts the insulin-response. Consequently, understanding these trafficking steps is an important research goal. The formation of GSVs and their insulin-stimulated translocation to, and fusion with, the plasma membrane are examples of regulated and specific membrane trafficking events. As such these events require SNARE proteins. This study has examined the functions of each of the members of the post-Golgi vSNAREs that make up the VAMP subfamily in the trafficking of GLUT4 into the insulin-sensitive compartment, as well as examining the contribution each of these vSNAREs plays in the SNARE complex involved in the insulin-stimulated translocation of GLUT4 to the cell surface. GLUT4 traffics through the endosomal system and the trans Golgi network (TGN) en route into GSVs in a process known to involve the t-SNARE syntaxin 16. In order to dissect the roles VAMP proteins play in the intracellular recycling and trafficking of GLUT4, the interactions of VAMP proteins with syntaxin 16 and its regulatory Sec-1/Munc-18 protein, mVps45 have been examined. Further, the effects of depletion of these VAMPs in GLUT4 distribution has been examined in HeLa cells expressing HA-GLUT4-GFP as a surrogate for adipose and muscle tissue. The fusion of GLUT4-containing vesicles with the cell surface in response to insulin stimulation is a key component of the insulin-response. Although there is consensus that tSNAREs involved in this process are syntaxin 4 and SNAP23, there is discord in the literature regarding the role each vSNARE plays in this fusion event. Many studies support a role for VAMP2, however recently it has been suggested that VAMPs 3 and 8 may also be involved. The roles of these VAMPs, as well as the other post-Golgi vSNAREs expressed in adipocytes, in the fusion of GLUT4-containing vesicles with the cell surface have been examined. This has been achieved through the characterisation of the expression level, subcellular distribution of the VAMPs and determination of associations that take place between each VAMP protein and the tSNARE complex made up of syntaxin 4 and SNAP23. The results from these experiments show that despite all VAMPs being capable of forming SDS-resistant SNARE complexes with either syntaxin 4 and SNAP23 or syntaxin 16 and SNAP23, in the cellular environment only VAMP2 interacts with syntaxin 4 and only VAMP4 interacts with syntaxin 16. This, alongside the finding that each VAMP protein is expressed at varying levels and localises with different pools of GLUT4, suggests that VAMP2, not VAMPs 3 or 8, is the major vSNARE involved in the trafficking of GLUT4 to the cell surface. The finding that VAMP4 is the only VAMP that interacts with syntaxin 16, alongside the results of VAMP depletion in HeLa cells expressing HA-GLUT4-GFP, support the hypothesis that VAMP4 is involved in sorting GLUT4 out of the endosomal pool and into GSVs.
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