Probing Polaron Clouds by Rydberg Atom Spectroscopy.

In recent years, Rydberg excitations in atomic quantum gases have become a successful platform to explore quantum impurity problems. A single impurity immersed in a Fermi gas leads to the formation of a polaron, a quasiparticle consisting of the impurity being dressed by the surrounding medium. With a radius of about the Fermi wavelength, the density profile of a polaron cannot be explored using in situ optical imaging techniques. In this Letter, we propose a new experimental measurement technique that enables the in situ imaging of the polaron cloud in ultracold quantum gases. The impurity atom induces the formation of a polaron cloud and is then excited to a Rydberg state. Because of the mesoscopic interaction range of Rydberg excitations, which can be tuned by the principal numbers of the Rydberg state, atoms extracted from the polaron cloud form dimers with the impurity. By performing first principle calculations of the absorption spectrum based on a functional determinant approach, we show how the occupation of the dimer state can be directly observed in spectroscopy experiments and can be mapped onto the density profile of the gas particles, hence providing a direct, real-time, and in situ measure of the polaron cloud.

A MoClo-Compatible Toolbox of ECF Sigma Factor-Based Regulatory Switches for Proteobacterial Chassis.

The construction of complex synthetic gene circuits with predetermined and reliable output depends on orthogonal regulatory parts that do not inadvertently interfere with the host machinery or with other circuit components. Previously, extracytoplasmic function sigma factors (ECFs), a diverse group of alternative sigma factors with distinct promoter specificities, were shown to have great potential as context-independent regulators, but so far, they have only been used in a few model species. Here, we show that the alphaproteobacterium Sinorhizobium meliloti, which has been proposed as a plant-associated bacterial chassis for synthetic biology, has a similar phylogenetic ECF acceptance range as the gammaproteobacterium Escherichia coli. A common set of orthogonal ECF-based regulators that can be used in both bacterial hosts was identified and used to create 2-step delay circuits. The genetic circuits were implemented in single copy in E. coli by chromosomal integration using an established method that utilizes bacteriophage integrases. In S. meliloti, we demonstrated the usability of single-copy pABC plasmids as equivalent carriers of the synthetic circuits. The circuits were either implemented on a single pABC or modularly distributed on 3 such plasmids. In addition, we provide a toolbox containing pABC plasmids compatible with the Golden Gate (MoClo) cloning standard and a library of basic parts that enable the construction of ECF-based circuits in S. meliloti and in E. coli. This work contributes to building a context-independent and species-overarching ECF-based toolbox for synthetic biology applications.

Tunable Feshbach Resonances and Their Spectral Signatures in Bilayer Semiconductors.

Feshbach resonances provide an invaluable tool in atomic physics, enabling precise control of interactions and the preparation of complex quantum phases of matter. Here, we theoretically analyze a solid-state analog of a Feshbach resonance in two dimensional semiconductor heterostructures. In the presence of interlayer electron tunneling, the scattering of excitons and electrons occupying different layers can be resonantly enhanced by tuning an applied electric field. The emergence of an interlayer Feshbach molecule modifies the optical excitation spectrum, and can be understood in terms of Fermi polaron formation. We discuss potential implications for the realization of correlated Bose-Fermi mixtures in bilayer semiconductors.

Design and Control of Extrachromosomal Elements in Methylorubrum extorquens AM1.

Genetic tools are a prerequisite to engineer cellular factories for synthetic biology and biotechnology. Methylorubrum extorquens AM1 is an important platform organism of a future C1-bioeconomy. However, its application is currently limited by the availability of genetic tools. Here we systematically tested repABC regions to maintain extrachromosomal DNA in M. extorquens. We used three elements to construct mini-chromosomes that are stably inherited at single copy number and can be shuttled between Escherichia coli and M. extorquens. These mini-chromosomes are compatible among each other and with high-copy number plasmids of M. extorquens. We also developed a set of inducible promoters of wide expression range, reaching levels exceeding those currently available, notably the PmxaF-promoter. In summary, we provide a set of tools to control the dynamic expression and copy number of genetic elements in M. extorquens, which opens new ways to unleash the metabolic and biotechnological potential of this organism for future applications.

A Family of Single Copy repABC-Type Shuttle Vectors Stably Maintained in the Alpha-Proteobacterium Sinorhizobium meliloti.

A considerable share of bacterial species maintains segmented genomes. Plant symbiotic α-proteobacterial rhizobia contain up to six repABC-type replicons in addition to the primary chromosome. These low or unit-copy replicons, classified as secondary chromosomes, chromids, or megaplasmids, are exclusively found in α-proteobacteria. Replication and faithful partitioning of these replicons to the daughter cells is mediated by the repABC region. The importance of α-rhizobial symbiotic nitrogen fixation for sustainable agriculture and Agrobacterium-mediated plant transformation as a tool in plant sciences has increasingly moved biological engineering of these organisms into focus. Plasmids are ideal DNA-carrying vectors for these engineering efforts. On the basis of repABC regions collected from α-rhizobial secondary replicons, and origins of replication derived from traditional cloning vectors, we devised the versatile family of pABC shuttle vectors propagating in Sinorhizobium meliloti, related members of the Rhizobiales, and Escherichia coli. A modular plasmid library providing the elemental parts for pABC vector assembly was founded. The standardized design of these vectors involves five basic modules: (1) repABC cassette, (2) plasmid-derived origin of replication, (3) RK2/RP4 mobilization site (optional), (4) antibiotic resistance gene, and (5) multiple cloning site flanked by transcription terminators. In S. meliloti, pABC vectors showed high propagation stability and unit-copy number. We demonstrated stable coexistence of three pABC vectors in addition to the two indigenous megaplasmids in S. meliloti, suggesting combinability of multiple compatible pABC plasmids. We further devised an in vivo cloning strategy involving Cre/lox-mediated translocation of large DNA fragments to an autonomously replicating repABC-based vector, followed by conjugation-mediated transfer either to compatible rhizobia or E. coli.

Automatic detection of microemboli during percutaneous coronary interventions.

The objective of this study was to develop an analysis method for the automatic detection of intracoronary microemboli triggered high intensity signals (HITS) during percutaneous coronary interventions (PCI). The recorded ultrasonic Doppler velocity spectra from an intracoronary ultrasonic guide-wire were decomposed into 13 wavelet scales applying the continuous wavelet transform. From 7 wavelet scales which were most suitable for a differentiation between HITS and pulsatile flow, envelopes were calculated and combined to improve the HITS-to-background noise ratio. For different intensity thresholds the resulting number of HITS was automatically counted and compared with the number estimated by experienced observers. In a first validation trial HITS were detected within a simplified in vitro model with a sensitivity of 89.2% and a positive predictive value of 87.6%. In a following clinical study 211 HITS from 18 patients during PCI were counted manually by the observers. With the developed wavelet-based method 189 HITS were correctly detected (sensitivity of 89.6%, positive predictive value of 85.5%). The introduced new method automatically detects intracoronary HITS for the first time with a reliable accuracy. This may support further studies evaluating the incidence and consequences of coronary microembolization during coronary interventions.