16 research outputs found
Systematic determination of the mosaic structure of bacterial genomes: species backbone versus strain-specific loops
BACKGROUND: Public databases now contain multitude of complete bacterial genomes, including several genomes of the same species. The available data offers new opportunities to address questions about bacterial genome evolution, a task that requires reliable fine comparison data of closely related genomes. Recent analyses have shown, using pairwise whole genome alignments, that it is possible to segment bacterial genomes into a common conserved backbone and strain-specific sequences called loops. RESULTS: Here, we generalize this approach and propose a strategy that allows systematic and non-biased genome segmentation based on multiple genome alignments. Segmentation analyses, as applied to 13 different bacterial species, confirmed the feasibility of our approach to discern the 'mosaic' organization of bacterial genomes. Segmentation results are available through a Web interface permitting functional analysis, extraction and visualization of the backbone/loops structure of documented genomes. To illustrate the potential of this approach, we performed a precise analysis of the mosaic organization of three E. coli strains and functional characterization of the loops. CONCLUSION: The segmentation results including the backbone/loops structure of 13 bacterial species genomes are new and available for use by the scientific community at the URL:
Spectroscopy of Colloidal Semiconductor Core/Shell Nanoplatelets with High Quantum Yield
Free
standing two-dimensional materials appear as a novel class
of structures. Recently, the first colloidal two-dimensional heterostructures
have been synthesized. These core/shell nanoplatelets are the first
step toward colloidal quantum wells. Here, we study in detail the
spectroscopic properties of this novel generation of colloidal nanoparticles.
We show that core/shell CdSe/CdZnS nanoplatelets with 80% quantum
yield can be obtained. The emission time trace of single core/shell
nanoplatelets exhibits reduced blinking compared to core nanoplatelets
with a two level emission time trace. At cryogenic temperatures, these
nanoplatelets have a quantum yield close to 100% and a stable emission
time trace. A solution of core/shell nanoplatelets has emission spectra
with a full width half-maximum close to 20 nm, a value much lower
than corresponding spherical or rod-shaped heterostructures. Using
single particle spectroscopy, we show that the broadening of the emission
spectra upon the shell deposition is not due to dispersity between
particles but is related to an intrinsic increased excitonâphonon
coupling in the shell. We also demonstrate that optical spectroscopy
is a relevant tool to investigate the presence of traps induced by
shell deposition. The spectroscopic properties of the core/shell nanoplatelets
presented here strongly suggest that this new generation of objects
will be an interesting alternative to spherical or rod-shaped nanocrystals