Bound states in the continuum in periodic photonic systems like photonic crystal slabs are proved to be accompanied by vortex polarization singularities on the photonic bands in the momentum space. The winding structures of polarization states not only widen the field of topological physics but also show great potential that such systems could be applied in polarization manipulating. In this work, we report the phenomenon that by in-plane inversion (C2) symmetry breaking, pairs of circularly polarized states could spawn from the eliminated Bound states in the continuum. Along with the appearance of the circularly polarized states as the two poles of the Poincaré sphere together with linearly polarized states covering the equator, full coverage on the Poincaré sphere could be realized. As an application, ellipticity modulation of linear polarization is demonstrated in the visible frequency range. This phenomenon provides new degree of freedom in modulating polarization.
Controlling the copy
number of gene expression cassettes is an
important strategy to engineer bacterial cells into high-efficiency
biocatalysts. Current strategies mostly use plasmid vectors, but multicopy
plasmids are often genetically unstable, and their copy numbers cannot
be precisely controlled. The integration of expression cassettes into
a bacterial chromosome has advantages, but iterative integration is
laborious, and it is challenging to obtain a library with varied gene
doses for phenotype characterization. Here, we demonstrated that multicopy
chromosomal integration using CRISPR-associated transposases (MUCICAT)
can be achieved by designing a crRNA to target multicopy loci or a
crRNA array to target multiple loci in the Escherichia coli genome. Within 5 days without selection pressure, E. coli strains carrying cargos with successively increasing copy numbers
(up to 10) were obtained. Recombinant MUCICAT E. coli containing genomic multicopy glucose dehydrogenase expression cassettes
showed 2.6-fold increased expression of this important industrial
enzyme compared to E. coli harboring
the conventional protein-expressing plasmid pET24a. Successful extension
of MUCICAT to Tatumella citrea further demonstrated
that MUCICAT may be generally applied to many bacterial species.
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