169 research outputs found
Intra-host symbiont diversity in eastern Pacific cold seep tubeworms identified by the 16S-V6 region, but undetected by the 16S-V4 region
Vestimentiferan tubeworms are key taxa in deep-sea chemosynthetic habitats worldwide. As adults they obtain their nutrition through their sulfide-oxidizing bacterial endosymbionts, which are acquired from the environment. Although horizontal transmission should favor infections by various symbiotic microbes, the current paradigm holds that every tubeworm harbors only one endosymbiotic 16S rRNA phylotype. Although previous studies based on traditional Sanger sequencing have questioned these findings, population level high-throughput analyses of the symbiont 16S diversity are still missing. To get further insights into the symbiont genetic variation and uncover hitherto hidden diversity we applied state-of-the-art 16S-V4 amplicon sequencing to populations of the co-occurring tubeworm species Lamellibrachia barhami and Escarpia spicata that were collected during E/V Nautilus and R/V Western Flyer cruises to cold seeps in the eastern Pacific Ocean. In agreement with earlier work our sequence data indicated that L. barhami and E. spicata share one monomorphic symbiont phylotype. However, complementary CARD-FISH analyses targeting the 16S-V6 region implied the existence of an additional phylotype in L. barhami. Our results suggest that the V4 region might not be sufficiently variable to investigate diversity in the intra-host symbiont population at least in the analyzed sample set. This is an important finding given that this region has become the standard molecular marker for high-throughput microbiome analyses. Further metagenomic research will be necessary to solve these issues and to uncover symbiont diversity that is hidden below the 16S rRNA level
Blood circulating miR-28-5p and let-7d-5p associate with premature ageing in Down syndrome
Persons with Down syndrome (DS) undergo a premature ageing with early onset of age-related diseases. The main endpoint of this study was the identification of blood circulating microRNAs (c-miRs) signatures characterizing DS ageing process. A discovery phase based on array was performed in plasma samples obtained from 3 young (31 ± 2 years-old) and 3 elderly DS persons (66 ± 2 years-old). Then, a validation phase was carried out for relevant miRs by RT-qPCR in an enlarged cohort of 43 DS individuals (from 19 up to 68 years-old). A group of 30 non-trisomic subjects, as representative of physiological ageing, was compared. In particular miR-628-5p, miR-152-3p, miR-28-5p, and let-7d-5p showed a lower level in younger DS persons (age ≤ 50 years) respect to the age-matched controls. Among those, miR-28-5p and let-7d-5p were found significantly decreased in physiological ageing ( oldest group ), thus they emerged as possible biomarkers of premature ageing in DS. Moreover, measuring blood levels of beta amyloid peptides, Aβ-42 was assessed at the lowest levels in physiological ageing and correlated with miR-28-5p and let-7d-5p in DS, while Aβ-40 correlated with miR-628-5p in the same cohort. New perspectives in terms of biomarkers are discussed
Photocurrent measurements of supercollision cooling in graphene
The cooling of hot electrons in graphene is the critical process underlying
the operation of exciting new graphene-based optoelectronic and plasmonic
devices, but the nature of this cooling is controversial. We extract the hot
electron cooling rate near the Fermi level by using graphene as novel
photothermal thermometer that measures the electron temperature () as it
cools dynamically. We find the photocurrent generated from graphene
junctions is well described by the energy dissipation rate , where the heat capacity is and is the
base lattice temperature. These results are in disagreement with predictions of
electron-phonon emission in a disorder-free graphene system, but in excellent
quantitative agreement with recent predictions of a disorder-enhanced
supercollision (SC) cooling mechanism. We find that the SC model provides a
complete and unified picture of energy loss near the Fermi level over the wide
range of electronic (15 to 3000 K) and lattice (10 to 295 K) temperatures
investigated.Comment: 7pages, 5 figure
Host-Microbe Interactions in the Chemosynthetic Riftia pachyptila Symbiosis
The deep-sea tubeworm Riftia pachyptila lacks a digestive system but completely relies on bacterial endosymbionts for nutrition. Although the symbiont has been studied in detail on the molecular level, such analyses were unavailable for the animal host, because sequence information was lacking. To identify host-symbiont interaction mechanisms, we therefore sequenced the Riftia transcriptome, which served as a basis for comparative metaproteomic analyses of symbiont-containing versus symbiont-free tissues, both under energy-rich and energy-limited conditions. Our results suggest that metabolic interactions include nutrient allocation from symbiont to host by symbiont digestion and substrate transfer to the symbiont by abundant host proteins. We furthermore propose that Riftia maintains its symbiont by protecting the bacteria from oxidative damage while also exerting symbiont population control. Eukaryote-like symbiont proteins might facilitate intracellular symbiont persistence. Energy limitation apparently leads to reduced symbiont biomass and increased symbiont digestion. Our study provides unprecedented insights into host-microbe interactions that shape this highly efficient symbiosis
Generation of photovoltage in graphene on a femtosecond time scale through efficient carrier heating
Graphene is a promising material for ultrafast and broadband photodetection.
Earlier studies addressed the general operation of graphene-based
photo-thermoelectric devices, and the switching speed, which is limited by the
charge carrier cooling time, on the order of picoseconds. However, the
generation of the photovoltage could occur at a much faster time scale, as it
is associated with the carrier heating time. Here, we measure the photovoltage
generation time and find it to be faster than 50 femtoseconds. As a
proof-of-principle application of this ultrafast photodetector, we use graphene
to directly measure, electrically, the pulse duration of a sub-50 femtosecond
laser pulse. The observation that carrier heating is ultrafast suggests that
energy from absorbed photons can be efficiently transferred to carrier heat. To
study this, we examine the spectral response and find a constant spectral
responsivity between 500 and 1500 nm. This is consistent with efficient
electron heating. These results are promising for ultrafast femtosecond and
broadband photodetector applications.Comment: 6 pages, 4 figure
Competing Ultrafast Energy Relaxation Pathways in Photoexcited Graphene
For most optoelectronic applications of graphene a thorough understanding of
the processes that govern energy relaxation of photoexcited carriers is
essential. The ultrafast energy relaxation in graphene occurs through two
competing pathways: carrier-carrier scattering -- creating an elevated carrier
temperature -- and optical phonon emission. At present, it is not clear what
determines the dominating relaxation pathway. Here we reach a unifying picture
of the ultrafast energy relaxation by investigating the terahertz
photoconductivity, while varying the Fermi energy, photon energy, and fluence
over a wide range. We find that sufficiently low fluence ( 4
J/cm) in conjunction with sufficiently high Fermi energy (
0.1 eV) gives rise to energy relaxation that is dominated by carrier-carrier
scattering, which leads to efficient carrier heating. Upon increasing the
fluence or decreasing the Fermi energy, the carrier heating efficiency
decreases, presumably due to energy relaxation that becomes increasingly
dominated by phonon emission. Carrier heating through carrier-carrier
scattering accounts for the negative photoconductivity for doped graphene
observed at terahertz frequencies. We present a simple model that reproduces
the data for a wide range of Fermi levels and excitation energies, and allows
us to qualitatively assess how the branching ratio between the two distinct
relaxation pathways depends on excitation fluence and Fermi energy.Comment: Nano Letters 201
Photoexcitation cascade and multiple hot-carrier generation in graphene
The conversion of light into free electron–hole pairs constitutes the key process in the fields of photodetection and photovoltaics. The efficiency of this process depends on the competition of different relaxation pathways and can be greatly enhanced when photoexcited carriers do not lose energy as heat, but instead transfer their excess energy into the production of additional electron–hole pairs through carrier–carrier scattering processes. Here we use optical pump–terahertz probe measurements to probe different pathways contributing to the ultrafast energy relaxation of photoexcited carriers. Our results indicate that carrier–carrier scattering is highly efficient, prevailing over optical-phonon emission in a wide range of photon wavelengths and leading to the production of secondary hot electrons originating from the conduction band. As hot electrons in graphene can drive currents, multiple hot-carrier generation makes graphene a promising material for highly efficient broadband extraction of light energy into electronic degrees of freedom, enabling high-efficiency optoelectronic applications.United States. Office of Naval Research (Grant N00014-09-1-0724
Intrinsic response time of graphene photodetectors
Graphene-based photodetectors are promising new devices for high-speed
optoelectronic applications. However, despite recent efforts, it is not clear
what determines the ultimate speed limit of these devices. Here, we present
measurements of the intrinsic response time of metal-graphene-metal
photodetectors with monolayer graphene using an optical correlation technique
with ultrashort laser pulses. We obtain a response time of 2.1 ps that is
mainly given by the short lifetime of the photogenerated carriers. This time
translates into a bandwidth of ~262 GHz. Moreover, we investigate the
dependence of the response time on gate voltage and illumination laser power
Dual-gated bilayer graphene hot electron bolometer
Detection of infrared light is central to diverse applications in security,
medicine, astronomy, materials science, and biology. Often different materials
and detection mechanisms are employed to optimize performance in different
spectral ranges. Graphene is a unique material with strong, nearly
frequency-independent light-matter interaction from far infrared to
ultraviolet, with potential for broadband photonics applications. Moreover,
graphene's small electron-phonon coupling suggests that hot-electron effects
may be exploited at relatively high temperatures for fast and highly sensitive
detectors in which light energy heats only the small-specific-heat electronic
system. Here we demonstrate such a hot-electron bolometer using bilayer
graphene that is dual-gated to create a tunable bandgap and
electron-temperature-dependent conductivity. The measured large electron-phonon
heat resistance is in good agreement with theoretical estimates in magnitude
and temperature dependence, and enables our graphene bolometer operating at a
temperature of 5 K to have a low noise equivalent power (33 fW/Hz1/2). We
employ a pump-probe technique to directly measure the intrinsic speed of our
device, >1 GHz at 10 K.Comment: 5 figure
Nutritional Factors Modulating Alu Methylation inan Italian Sample from The Mark-Age StudyIncluding Offspring of Healthy Nonagenarians
Alu hypomethylation promotes genomic instability and is associated with aging and
age-related diseases. Dietary factors affect global DNA methylation, leading to
changes in genomic stability and gene expression with an impact on longevity and
the risk of disease. This preliminary study aims to investigate the relationship
between nutritional factors, such as circulating trace elements, lipids and
antioxidants, and Alu methylation in elderly subjects and offspring of healthy
nonagenarians. Alu DNA methylation was analyzed in sixty RASIG (randomly
recruited age-stratified individuals from the general population) and thirty-two
GO (GeHA offspring) enrolled in Italy in the framework of the MARK-AGE project.
Factor analysis revealed a different clustering between Alu CpG1 and the other
CpG sites. RASIG over 65 years showed lower Alu CpG1 methylation than those of GO
subjects in the same age class. Moreover, Alu CpG1 methylation was associated
with fruit and whole-grain bread consumption, LDL2-Cholesterol and plasma copper.
The preserved Alu methylation status in GO, suggests Alu epigenetic changes as a
potential marker of aging. Our preliminary investigation shows that Alu
methylation may be affected by food rich in fibers and antioxidants, or
circulating LDL subfractions and plasma copper
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