225 research outputs found
Better under stress: Improving bacterial cellulose production by Komagataeibacter xylinus K2G30 (UMCC 2756) using adaptive laboratory evolution
Among naturally produced polymers, bacterial cellulose is receiving enormous attention due to remarkable properties, making it suitable for a wide range of industrial applications. However, the low yield, the instability of microbial strains and the limited knowledge of the mechanisms regulating the metabolism of producer strains, limit the large-scale production of bacterial cellulose. In this study, Komagataeibacter xylinus K2G30 was adapted in mannitol based medium, a carbon source that is also available in agri-food wastes. K. xylinus K2G30 was continuously cultured by replacing glucose with mannitol (2% w/v) for 210 days. After a starting lag-phase, in which no changes were observed in the utilization of mannitol and in bacterial cellulose production (cycles 1-25), a constant improvement of the phenotypic performances was observed from cycle 26 to cycle 30, accompanied by an increase in mannitol consumption. At cycle 30, the end-point of the experiment, bacterial cellulose yield increased by 38% in comparision compared to cycle 1. Furthermore, considering the mannitol metabolic pathway, D-fructose is an intermediate in the bioconversion of mannitol to glucose. Based on this consideration, K. xylinus K2G30 was tested in fructose-based medium, obtaining the same trend of bacterial cellulose production observed in mannitol medium. The adaptive laboratory evolution approach used in this study was suitable for the phenotypic improvement of K. xylinus K2G30 in bacterial cellulose production. Metabolic versatility of the strain was confirmed by the increase in bacterial cellulose production from D-fructose-based medium. Moreover, the adaptation on mannitol did not occur at the expense of glucose, confirming the versatility of K2G30 in producing bacterial cellulose from different carbon sources. Results of this study contribute to the knowledge for designing new strategies, as an alternative to the genetic engineering approach, for bacterial cellulose production
X-linked heterochromatin distribution in the holocentric chromosomes of the green apple aphid Aphis pomi
Chromatin organization in the holocentric chromosomes of the green apple aphid Aphis pomi has been investigated at a cytological level after C-banding, NOR, Giemsa, fluorochrome staining and fluorescent in situ hybridization (FISH). C-banding technique showed that heterochromatic bands are exclusively located on X chromosomes. This data represents a peculiar feature that clearly contradicts the equilocal distribution of heterochromatin typical of monocentric chromosomes. Moreover, silver staining and FISH carried out with a 28S rDNA probe localized rDNA genes on one telomere of each X chromosome; CMA(3) staining reveals that these silver positive telomeres are, the only GC-rich regions among A. pomi heterochromatin, whereas all other C-positive bands are DAPI positive thus containing AT-rich DNA
Strange metal electrodynamics across the phase diagram of Bi<sub>2-<i>x</i></sub>Pb<sub><i>x</i></sub>Sr<sub>2-<i>y</i></sub>La<sub><i>y</i></sub>CuO<sub>6+<i>δ</i></sub> cuprates
Unlocking the mystery of the strange metal state has become the focal point of high-Tcresearch, not because of its importance for superconductivity, but because it appears to represent a truly novel phase of matter dubbed "quantum supreme matter. " Detected originally through high magnetic field, transport experiments, signatures of this phase have now been uncovered with a variety of probes. Our high resolution optical data of the low-Tccuprate superconductor, Bi2-xPbxSr2-yLayCuO6+delta allows us to probe this phase over a large energy and temperature window. We demonstrate that the optical signatures of the strange metal phase persist throughout the phase diagram. The strange metal signatures in the optical conductivity are twofold: (i) a low energy Drude response with Drude width on the order of temperature and (ii) a high energy conformal tail with a doping dependent power-law exponent. While the Drude weight evolves monotonically throughout the entire doping range studied, the spectral weight contained in the high energy conformal tail appears to be doping and temperature independent. Our analysis further shows that the temperature dependence of the optical conductivity is completely determined by the Drude parameters. Our results indicate that there is no critical doping level inside the superconducting dome where the carrier density starts to change drastically and that the previously observed "return to normalcy " is a consequence of the increasing importance of the Drude component relative to the conformal tail with doping. Importantly, both the doping and temperature dependence of the resistivity are largely determined by the Drude width
A user-friendly nomogram to predict relapse-free survival (RFS) in western patients with resected gastric cancer (GC)
Immune-inflammatory and clinicopathologic prognostic factors in a Western cohort of resected gastric cancers (GCs)
Revealing the Dynamic Magneto-ionic Environments of Repeating Fast Radio Burst Sources through Multi-year Polarimetric Monitoring with CHIME/FRB
Fast radio bursts (FRBs) display a confounding variety of burst properties
and host galaxy associations. Repeating FRBs offer insight into the FRB
population by enabling spectral, temporal and polarimetric properties to be
tracked over time. Here, we report on the polarized observations of 12
repeating sources using multi-year monitoring with the Canadian Hydrogen
Intensity Mapping Experiment (CHIME) over 400-800 MHz. We observe significant
RM variations from many sources in our sample, including RM changes of several
hundred over month timescales from FRBs 20181119A,
20190303A and 20190417A, and more modest RM variability ( few tens rad m) from FRBs 20181030A, 20190208A, 20190213B and
20190117A over equivalent timescales. Several repeaters display a frequency
dependent degree of linear polarization that is consistent with depolarization
via scattering. Combining our measurements of RM variations with equivalent
constraints on DM variability, we estimate the average line-of-sight magnetic
field strength in the local environment of each repeater. In general, repeating
FRBs display RM variations that are more prevalent/extreme than those seen from
radio pulsars in the Milky Way and the Magellanic Clouds, suggesting repeating
FRBs and pulsars occupy distinct magneto-ionic environments
Proposed host galaxies of repeating fast radio burst sources detected by CHIME/FRB
We present a search for host galaxy associations for the third set of
repeating fast radio burst (FRB) sources discovered by the CHIME/FRB
Collaboration. Using the ~1 arcmin CHIME/FRB baseband localizations and
probabilistic methods. We identify potential host galaxies of two FRBs,
20200223B and 20190110C at redshifts of 0.06024(2) and 0.12244(6),
respectively. We also discuss the properties of a third marginal candidate host
galaxy association for FRB 20191106C with a host redshift of 0.10775(1). The
three putative host galaxies are all relatively massive, fall on the standard
mass-metallicity relationship for nearby galaxies, and show evidence of ongoing
star formation. They also all show signatures of being in a transitional
regime, falling in the "green valley" which is between the bulk of star-forming
and quiescent galaxies. The plausible host galaxies identified by our analysis
are consistent with the overall population of repeating and non-repeating FRB
hosts while increasing the fraction of massive and bright galaxies. Coupled
with these previous host associations, we identify a possible excess of FRB
repeaters whose host galaxies have M_u - M_r colors redder than the bulk of
star-forming galaxies. Additional precise localizations are required to confirm
this trend.Comment: 11 pages, submitted to AAS journal
Limits on Fast Radio Burst-like Counterparts to Gamma-Ray Bursts Using CHIME/FRB
Fast radio bursts (FRBs) are a class of highly energetic, mostly extragalactic radio transients lasting for ∼milliseconds. While over 600 FRBs have been published so far, their origins are presently unclear, with some theories for extragalactic FRBs predicting accompanying high-energy emission. In this work, we use the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Fast Radio Burst (CHIME/FRB) Project to explore whether any FRB-like radio emission coincides in space and time with 81 gamma-ray bursts (GRBs) detected between 2018 July 17 and 2019 July 8 by Swift/BAT and Fermi/GBM. We do not find any statistically significant coincident pairs within 3σ of each other's spatial localization regions and within a time difference of up to one week. In addition to searching for spatial matches between known FRBs and known GRBs, we use CHIME/FRB to constrain FRB-like (∼1-10 ms) radio emission before, at the time of, or after the reported high-energy emission at the position of 39 GRBs. For short gamma-ray bursts (SGRBs), we constrain the radio flux in the 400--800 MHz band to be under a few kJy for ∼5.5-12.5 hr post-high-energy burst. We use these limits to constrain models that predict FRB-like prompt radio emission after SGRBs. For long gamma-ray bursts, we constrain the radio flux to be under a few kJy from ∼6 hr pre-high-energy burst to ∼12 hr post-high-energy burst
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