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  • 1
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    Effects of MreB paralogs on poly-{gamma}-glutamic acid synthesis and cell morphology in Bacillus amyloliquefaciens (2016)
    Oxford University Press
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    Publication Date: 2016-08-27
    Description: Actin-like MreB paralogs play important roles in cell shape maintenance, cell wall synthesis and the regulation of the D,L-endopeptidases, CwlO and LytE. The gram-positive bacteria, Bacillus amyloliquefaciens LL3, is a poly--glutamic acid (-PGA) producing strain that contains three MreB paralogs: MreB, Mbl and MreBH. In B. amyloliquefaciens , CwlO and LytE can degrade -PGA. In this study, we aimed to test the hypothesis that modulating transcript levels of MreB paralogs would alter the synthesis and degradation of -PGA. The results showed that overexpression or inhibition of MreB, Mbl or MreBH had distinct effects on cell morphology and the molecular weight of the -PGA products. In fermentation medium, cells of mreB inhibition mutant were 50.2% longer than LL3, and the -PGA titer increased by 55.7%. However, changing the expression level of mbl showed only slight effects on the morphology, -PGA molecular weight and titer. In the mreBH inhibition mutant, -PGA production and its molecular weight increased by 56.7% and 19.4%, respectively. These results confirmed our hypothesis that suppressing the expression of MreB paralogs might reduce -PGA degradation, and that improving the cell size could strengthen -PGA synthesis. This is the first report of enhanced -PGA production via suppression of actin-like MreB paralogs.
    Keywords: Biotechnology & Synthetic Biology
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
    Published by Oxford University Press
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  • 2
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    Insights into the location and dynamics of the coolest X-ray emitting gas in clusters of galaxies (2016)
    Oxford University Press
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    Publication Date: 2016-07-13
    Description: We extend our previous study of the cool gas responsible for the emission of O vii X-ray lines in the cores of clusters and groups of galaxies. This is the coolest X-ray emitting phase and connects the 10 000 K H α emitting gas to the million degree phase, providing a useful tool to understand cooling in these objects. We study the location of the O vii gas and its connection to the intermediate Fe xvii and hotter O viii phases. We use high-resolution X-ray grating spectra of elliptical galaxies with strong Fe xvii line emission and detect O vii in 11 of 24 objects. Comparing the O vii detection level and resonant scattering, which is sensitive to turbulence and temperature, suggests that O vii is preferably found in cooler objects, where the Fe xvii resonant line is suppressed due to resonant scattering, indicating subsonic turbulence. Although a larger sample of sources and further observations is needed to distinguish between effects from temperature and turbulence, our results are consistent with cooling being suppressed at high turbulence as predicted by models of active galactic nuclei feedback, gas sloshing and galactic mergers. In some objects, the O vii resonant-to-forbidden line ratio is decreased by either resonant scattering or charge exchange boosting the forbidden line, as we show for NGC 4636. Charge exchange indicates interaction between neutral and ionized gas phases. The Perseus cluster also shows a high Fe xvii forbidden-to-resonance line ratio, which can be explained with resonant scattering by low-turbulence cool gas in the line of sight.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    The first Doppler images of the eclipsing binary SZ Piscium (2015)
    Oxford University Press
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    Publication Date: 2015-12-16
    Description: We present the first Doppler images of the active eclipsing binary system SZ Psc, based on the high-resolution spectral data sets obtained in 2004 November and 2006 September–December. The least-squares deconvolution technique was applied to derive high signal-to-noise profiles from the observed spectra of SZ Psc. Absorption features contributed by a third component of the system were detected in the LSD profiles at all observed phases. We estimated the mass and period of the third component to be about 0.9 M and 1283 ± 10 d, respectively. After removing the contribution of the third body from the least-squares deconvolved profiles, we derived the surface maps of SZ Psc. The resulting Doppler images indicate significant star-spot activities on the surface of the K subgiant component. The distributions of star-spots are more complex than that revealed by previous photometric studies. The cooler K component exhibited pronounced high-latitude spots as well as numerous low- and intermediate-latitude spot groups during the entire observing seasons, but did not show any large, stable polar cap, different from many other active RS CVn-type binaries.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Distribution and evolution of starspots on the RS CVn binary II Pegasi in 2004 (2014)
    Oxford University Press
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    Publication Date: 2014-02-15
    Description: We present Doppler images of RS CVn-type binary II Peg based on two data sets obtained in 2004 February and November. In order to improve signal-to-noise ratio and reliability, we apply least-squares deconvolution technique to calculate average profiles from 2032 photospheric absorption lines. Both of the resulting surface images show a wide latitude distribution of starspots. Most spots are concentrated at a high-latitude belt above 60° and a low-latitude belt near equator. The starspots evolved dramatically between two observing runs, which may indicate shorter time-scale evolution in this epoch, especially for low-latitude belt. There is no stable preferred active longitude that can be found in our images. We also find out a possible phenomenon that the intermediate-latitude spot migrated poleward and merged with the high-latitude spot to make it stronger, which may reveal a more complex behaviour of starspots on II Peg. A potential change of orbital ephemeris zero-point was detected. This may imply an orbital period change of II Peg like other active close binaries.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Doppler images of the eclipsing binary ER Vulpeculae (2014)
    Oxford University Press
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    Publication Date: 2014-12-20
    Description: We present Doppler images of both components of the eclipsing binary system ER Vul, based on the spectra obtained in 2004 November, 2006 September and 2008 November. The least-squares deconvolution technique is used for enhancing the signal-to-noise ratios of the observed profiles. The new surface images reveal that both stars of ER Vul show strong starspot activities and the starspots appear at various latitudes. The surface maps of 2006 and 2008 both show the presence of large high-latitude starspots on each component of ER Vul. We find no obvious phase shift of the active regions during our observations. The longitude distributions of starspots are non-uniform on both stars. At low-to-mid latitudes, the active regions are almost exclusively found in the hemisphere facing the other star. However, we find no pronounced concentration of spots at the sub-stellar points.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Doppler images of the eclipsing binary ER Vulpeculae (2014)
    Oxford University Press
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    Publication Date: 2014-12-29
    Description: We present Doppler images of both components of the eclipsing binary system ER Vul, based on the spectra obtained in 2004 November, 2006 September and 2008 November. The least-squares deconvolution technique is used for enhancing the signal-to-noise ratios of the observed profiles. The new surface images reveal that both stars of ER Vul show strong starspot activities and the starspots appear at various latitudes. The surface maps of 2006 and 2008 both show the presence of large high-latitude starspots on each component of ER Vul. We find no obvious phase shift of the active regions during our observations. The longitude distributions of starspots are non-uniform on both stars. At low-to-mid latitudes, the active regions are almost exclusively found in the hemisphere facing the other star. However, we find no pronounced concentration of spots at the sub-stellar points.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Genotypic heterogeneity of emetic toxin producing Bacillus cereus isolates from China (2017)
    Oxford University Press
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    Publication Date: 2017-01-19
    Description: Emetic toxin-producing Bacillus cereus (emetic B. cereus ) is the third member of B. cereus group whose toxins are encoded by megaplasmids, beside anthrax and insecticidal toxins of B. anthracis and B. thuringiensis , respectively. A total of 18 emetic isolates collected from food poisoning events, clinical and non-random food samples in Zhejiang province of China, were analyzed by plasmid screening, pulse field gel electrophoresis, multilocus sequence typing, and toxic gene identification to investigate their genotypic diversity. In this study, 13 plasmid profile types, 14 pulse types and 6 different STs from emetic isolates were detected, in which ST 1035,1038,1053,1054 and 1065 were first assigned and reported. The toxic gene ces existed on its own, or coexisted with other toxic genes bceT, cytk, entFM and nhe , but never with hbl in emetic isolates. The results demonstrated that the emetic B. cereus strains from China were heterologous at genotypic level.
    Keywords: Food Microbiology
    Print ISSN: 0378-1097
    Electronic ISSN: 1574-6968
    Topics: Biology
    Published by Oxford University Press
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  • 8
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    Development of an inducible transposon system for efficient random mutagenesis in Clostridium acetobutylicum (2016)
    Oxford University Press
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    Publication Date: 2016-04-15
    Description: Clostridium acetobutylicum is an industrially important Gram-positive organism, which is capable of producing economically important chemicals in the ABE (Acetone, Butanol and Ethanol) fermentation process. Renewed interests in the ABE process necessitate the availability of additional genetics tools to facilitate the derivation of a greater understanding of the underlying metabolic and regulatory control processes in operation through forward genetic strategies. In this study, a xylose inducible, mariner -based, transposon system was developed and shown to allow high-efficient random mutagenesis in the model strain ATCC 824. Of the thiamphenicol resistant colonies obtained, 91.9% were shown to be due to successful transposition of the catP- based mini-transposon element. Phenotypic screening of 200 transposon clones revealed a sporulation-defective clone with an insertion in spo0A , thereby demonstrating that this inducible transposon system can be used for forward genetic studies in C. acetobutylicum .
    Keywords: Biotechnology & Synthetic Biology
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    Electronic ISSN: 1574-6968
    Topics: Biology
    Published by Oxford University Press
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  • 9
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    Insight-HXMT observations of Swift J0243.6+6124: the evolution of RMS pulse fractions at super-Eddington luminosity (2020)
    Oxford University Press
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    Publication Date: 2020-08-17
    Description: Based on Insight-HXMT data, we report on the pulse fraction evolution during the 2017–2018 outburst of the newly discovered first Galactic ultraluminous X-ray (ULX) source Swift J0243.6+6124. The pulse fractions of 19 observation pairs selected in the rising and fading phases with similar luminosity are investigated. The results show a general trend of the pulse fraction increasing with luminosity and energy at supercritical luminosity. However, the relative strength of the pulsation between each pair evolves strongly with luminosity. The pulse fraction in the rising phase is larger at luminosity below 7.71 × 1038 erg s−1, but smaller at above. A transition luminosity is found to be energy independent. Such a phenomenon is first confirmed by Insight-HXMT observations and we speculate that it may have relation with the radiation-pressure-dominated accretion disc.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 10
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    Timing analysis of 2S 1417-624 observed with NICER and Insight-HXMT (2019)
    Oxford University Press
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    Publication Date: 2019-10-22
    Description: We present a study of timing properties of the accreting pulsar 2S 1417-624 observed during its 2018 outburst, based on Swift/BAT, Fermi/GBM, Insight-HXMT and NICER observations. We report a dramatic change of the pulse profiles with luminosity. The morphology of the profile in the range 0.2-10.0 keV switches from double to triple peaks at ∼2.5 $ m imes 10^{37}{it D}_{10}^2 erg s^{-1}$ and from triple to quadruple peaks at ∼7 $ m imes 10^{37}{it D}_{10}^2 erg s^{-1}$. The profile at high energies (25-100 keV) shows significant evolutions as well. We explain this phenomenon according to existing theoretical models. We argue that the first change is related to the transition from the sub to the super-critical accretion regime, while the second to the transition of the accretion disc from the gas-dominated to the radiation pressure-dominated state. Considering the spin-up as well due to the accretion torque, this interpretation allows to estimate the magnetic field self-consistently at ∼7 × 1012 G.
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    Topics: Physics
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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