487 research outputs found
Extended hopanoid loss reduces bacterial motility and surface attachment, and leads to heterogeneity in root nodule growth kinetics in a Bradyrhizobium-Aeschynomene symbiosis
Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Roughly 10% of bacteria contain genes involved in hopanoid biosynthesis, and these genes are particularly conserved in plant-associated organisms. We previously found that the extended class of hopanoids (C35) in the nitrogen-fixing soil bacterium Bradyrhizobium diazoefficiens promotes its root nodule symbiosis with the tropical legume Aeschynomene afraspera. By quantitatively modeling root nodule development, we identify independent consequences of extended hopanoid loss in the initiation of root nodule formation and in the rate of root nodule maturation. In vitro studies demonstrate that extended hopanoids support B. diazoefficiens motility and surface attachment, which may correlate with stable root colonization in planta. Confocal microscopy of maturing root nodules reveals that root nodules infected with extended hopanoid-deficient B. diazoefficiens contain unusually low densities of bacterial symbionts, indicating that extended hopanoids are necessary for persistent, high levels of host infection
Wannier-Stark ladders in one-dimensional elastic systems
The optical analogues of Bloch oscillations and their associated
Wannier-Stark ladders have been recently analyzed. In this paper we propose an
elastic realization of these ladders, employing for this purpose the torsional
vibrations of specially designed one-dimensional elastic systems. We have
measured, for the first time, the ladder wave amplitudes, which are not
directly accessible either in the quantum mechanical or optical cases. The wave
amplitudes are spatially localized and coincide rather well with theoretically
predicted amplitudes. The rods we analyze can be used to localize different
frequencies in different parts of the elastic systems and viceversa.Comment: 10 pages, 6 figures, accepted in Phys. Rev. Let
Efficacy of face coverings in reducing transmission of COVID-19:Calculations based on models of droplet capture
In the COVID--19 pandemic, among the more controversial issues is the use of
masks and face coverings. Much of the concern boils down to the question --
just how effective are face coverings? One means to address this question is to
review our understanding of the physical mechanisms by which masks and
coverings operate -- steric interception, inertial impaction, diffusion and
electrostatic capture. We enquire as to what extent these can be used to
predict the efficacy of coverings. We combine the predictions of the models of
these mechanisms which exist in the filtration literature and compare the
predictions with recent experiments and lattice Boltzmann simulations, and find
reasonable agreement with the former and good agreement with the latter.
Building on these results, we explore the parameter space for woven cotton
fabrics to show that three-layered cloth masks can be constructed with
comparable filtration performance to surgical masks under ideal conditions.
Reusable cloth masks thus present an environmentally friendly alternative to
surgical masks so long as the face seal is adequate enough to minimise leakage.Comment: 26 pages (13 + references, 10 pages supplementary), 10 figures (8 in
main text, 2 in SI); accepted version, to appear in Physics of Fluids'
special issue "Flow and the Virus
Decorated networks of native proteins:nanomaterials with tunable mesoscopic domain size
Natural and artificial proteins with designer properties and functionalities offer unparalleled opportunity for functional nanoarchitectures formed through self-assembly. However, to exploit this potential we need to design the system such that assembly results in desired architecture forms while avoiding denaturation and therefore retaining protein functionality. Here we address this challenge with a model system of fluorescent proteins. By manipulating self-assembly using techniques inspired by soft matter where interactions between the components are controlled to yield the desired structure, we have developed a methodology to assemble networks of proteins of one species which we can decorate with another, whose coverage we can tune. Consequently, the interfaces between domains of each component can also be tuned, with potential applications for example in energy - or electron - transfer. Our model system of eGFP and mCherry with tuneable interactions reveals control over domain sizes in the resulting networks
The importance of lizards and small mammals as reservoirs for Borrelia lusitaniae in Portugal
Borrelia lusitaniae is a pathogen frequent in the Mediterranean area. Apart from lizards, evidence for birds and small mammals as competent reservoirs for this genospecies has been occasional. We collected questing ticks, skin biopsies and Ixodes sp. ticks feeding on lizards, birds and small mammals in a B. burgdorferi s.l. enzootic area to assess their importance in the maintenance of B. lusitaniae. B. lusitaniae was the most prevalent genospecies in questing ticks and was commonly found in larvae feeding on Psammodromus algirus. One biopsy infected with B. lusitaniae was collected from the tail of one Podarcis hispanica, which suggests systemic infection. I. ricinus larvae feeding on Apodemus sylvaticus were infected with B. lusitaniae but with a lower prevalence. Our results reinforce the importance of lizards as reservoirs for B. lusitaniae, suggesting that P. algirus, in particular, acts as main reservoir for B. lusitaniae in Portugal
How effective are face coverings in reducing transmission of COVID-19?
In the COVID-19 pandemic, among the more controversial issues is the use of
face coverings. To address this we show that the underlying physics ensures
particles with diameters & 1 m are efficiently filtered out by a simple
cotton or surgical mask. For particles in the submicron range the efficiency
depends on the material properties of the masks, though generally the
filtration efficiency in this regime varies between 30 to 60 % and
multi-layered cotton masks are expected to be comparable to surgical masks.
Respiratory droplets are conventionally divided into coarse droplets (> 5-10
m) responsible for droplet transmission and aerosols (< 5-10 m)
responsible for airborne transmission. Masks are thus expected to be highly
effective at preventing droplet transmission, with their effectiveness limited
only by the mask fit, compliance and appropriate usage. By contrast, knowledge
of the size distribution of bioaerosols and the likelihood that they contain
virus is essential to understanding their effectiveness in preventing airborne
transmission. We argue from literature data on SARS-CoV-2 viral loads that the
finest aerosols (< 1 m) are unlikely to contain even a single virion in
the majority of cases; we thus expect masks to be effective at reducing the
risk of airborne transmission in most settings.Comment: 5 pages + references, 3 figure
Extended hopanoid loss reduces bacterial motility and surface attachment, and leads to heterogeneity in root nodule growth kinetics in a Bradyrhizobium-Aeschynomene symbiosis
Hopanoids are steroid-like bacterial lipids that enhance membrane rigidity and promote bacterial growth under diverse stresses. Roughly 10% of bacteria contain genes involved in hopanoid biosynthesis, and these genes are particularly conserved in plant-associated organisms. We previously found that the extended class of hopanoids (C35) in the nitrogen-fixing soil bacterium Bradyrhizobium diazoefficiens promotes its root nodule symbiosis with the tropical legume Aeschynomene afraspera. By quantitatively modeling root nodule development, we identify independent consequences of extended hopanoid loss in the initiation of root nodule formation and in the rate of root nodule maturation. In vitro studies demonstrate that extended hopanoids support B. diazoefficiens motility and surface attachment, which may correlate with stable root colonization in planta. Confocal microscopy of maturing root nodules reveals that root nodules infected with extended hopanoid-deficient B. diazoefficiens contain unusually low densities of bacterial symbionts, indicating that extended hopanoids are necessary for persistent, high levels of host infection
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