59 research outputs found
Infrared regularization with spin-3/2 fields
We present a Lorentz-invariant formulation of baryon chiral perturbation
theory including spin-3/2 fields. Particular attention is paid to the
projection on the spin-3/2 components of the delta fields. We also discuss the
nucleon mass and the pion-nucleon sigma term.Comment: 9 pp, 1 fi
Plant-Derived Catechols Are Substrates of TonB-Dependent Transporters and Sensitize Pseudomonas aeruginosa to Siderophore-Drug Conjugates
Pseudomonas aeruginosa is an opportunistic pathogen responsible for acute and chronic infections in immunocompromised hosts. This organism is known to compete efficiently against coinfecting microorganisms, due in part to the secretion of antimicrobial molecules and the synthesis of siderophore molecules with high affinity for iron. P. aeruginosa possess a large repertoire of TonB-dependent transporters for the uptake of its own, as well as xenosiderophores released from other bacteria or fungi. Here, we show that P. aeruginosa is also capable of utilizing plant-derived polyphenols as an iron source. We found that exclusively plant-derived phenols containing a catechol group (i.e., chlorogenic acid, caffeic acid, quercetin, luteolin) induce the expression of the TonB-dependent transporters PiuA or PirA. This induction requires the two-component system PirR-PirS. Chlorogenic acid in its Fe(III)-loaded form was actively transported by PiuA and PirA and supported growth under iron-limiting conditions. Coincidentally, PiuA and PirA are also the main TonB transporters for the recently approved siderophore-drug conjugate cefiderocol. Surprisingly, quercetin supplementation increased the susceptibility of P. aeruginosa to siderophore-drug conjugates, due to induction of; piuA; and; pirA; expression mediated by the PirR-PirS two-component system. These findings suggest a potential novel therapeutic application for these biologically active dietary polyphenols.; IMPORTANCE; Iron is an essential element for living organisms. Most bacteria synthesize species-specific iron chelators, called siderophores, able to capture iron from their host or the environment. Pseudomonas aeruginosa, an opportunistic pathogen, produces two endogenous siderophores but is able to acquire iron also via xenosiderophores, produced by other bacteria or fungi, using a set of conserved TonB transporters. Here, we show that P. aeruginosa is also able to use plant metabolites, like quercetin and chlorogenic acid, as siderophores. These metabolites possess an iron-chelating catechol group and are recognized and transported by the TonB transporters PirA and PiuA. Since these transporters also promote the specific uptake of siderophore-drug conjugates, P. aeruginosa exposed to these plant catechols becomes hypersusceptible to this novel class of antibiotics. This unexpected finding suggests a potential therapeutic application for quercetin and chlorogenic acid, which were mainly investigated for their antioxidant and anti-inflammatory properties
Chiral Extrapolations and the Covariant Small Scale Expansion
We calculate the nucleon and the delta mass to fourth order in a covariant
formulation of the small scale expansion. We analyze lattice data from the MILC
collaboration and demonstrate that the available lattice data combined with our
knowledge of the physical values for the nucleon and delta masses lead to
consistent chiral extrapolation functions for both observables up to fairly
large pion masses. This holds in particular for very recent data on the delta
mass from the QCDSF collaboration. The resulting pion-nucleon sigma term is
sigma_{piN} = 48.9 MeV. This first quantitative analysis of the quark-mass
dependence of the structure of the Delta(1232) in full QCD within chiral
effective field theory suggests that (the real part of) the nucleon-delta
mass-splitting in the chiral limit, Delta_0 = 0.33 GeV, is slightly larger than
at the physical point. Further analysis of simultaneous fits to nucleon and
delta lattice data are needed for a precision determination of the properties
of the first excited state of the nucleon.Comment: 11 pp, 2 figs, version accepted for publication in Phys. Lett.
Trojan Horse Siderophore Conjugates Induce Pseudomonas aeruginosa Suicide and Qualify the TonB Protein as a Novel Antibiotic Target
Rising infection rates with multidrug-resistant pathogens calls for antibiotics with novel modes of action. Herein, we identify the inner membrane protein TonB, a motor of active uptake in Gram-negative bacteria, as a novel target in antimicrobial therapy. The interaction of the TonB box of outer membrane transporters with TonB is crucial for the internalization of essential metabolites. We designed TonB box peptides and coupled them with synthetic siderophores in order to facilitate their uptake into bacteria in up to 32 synthetic steps. Three conjugates repressed the growth of Pseudomonas aeruginosa cells unable to produce their own siderophores, with minimal inhibitory concentrations between 0.1 and 0.5 μM. The transporters mediating uptake of these compounds were identified as PfeA and PirA. The study illustrates a variant of cellular suicide where a transporter imports its own inhibitor and demonstrates that artificial siderophores can import cargo with molecular weights up to 4 kDa
Consistent Calculation of the Nucleon Electromagnetic Polarizabilities in Chiral Perturbation Theory Beyond Next-to-Leading Order
We calculate the nucleons' electromagnetic polarizabilities in heavy baryon
chiral perturbation theory including all terms to order . The
chiral prediction of the electric polarizabilities for the neutron and the
proton are in good agreement with the data. In the case of the magnetic
polarizabilities the big positive contribution from the
resonance is largely cancelled by a non--analytic loop contribution of the type. This novel effect helps to understand the rather small empirical
value of the nucleons' magnetic polarizability.Comment: 10 pp, TeX, BUTP-93/22 and CRN-93-3
The nucleon axial-vector coupling beyond one loop
We analyze the nucleon axial-vector coupling to two loops in chiral
perturbation theory. We show that chiral extrapolations based on this
representation require lattice data with pion masses below 300 MeV.Comment: 9 pp, 2 fig
Dispersive representation and shape of the Kl3 form factors: robustness
An accurate low-energy dispersive parametrization of the scalar Kpi form
factor was constructed some time ago in terms of a single parameter guided by
the Callan-Treiman low-energy theorem. A similar twice subtracted dispersive
parametrization for the vector Kpi form factor will be investigated here. The
robustness of the parametrization of these two form factors will be studied in
great detail. In particular the cut-off dependence, the isospin breaking
effects and the possible, though not highly probable, presence of zeros in the
form factors will be discussed. Interesting constraints in the latter case will
be obtained from the soft-kaon analog of the Callan-Treiman theorem and a
comparison with the recent tau --> K pi nu_tau data.Comment: 24 pages, 11 figure
Chiral Extrapolation of the Strangeness Changing K pi Form Factor
We perform a chiral extrapolation of lattice data on the scalar K pi form
factor and the ratio of the kaon and pion decay constants within Chiral
Perturbation Theory to two loops. We determine the value of the scalar form
factor at zero momentum transfer, at the Callan-Treiman point and at its soft
kaon analog as well as its slope. Results are in good agreement with their
determination from experiment using the standard couplings of quarks to the W
boson. The slope is however rather large. A study of the convergence of the
chiral expansion is also performed.Comment: few minor change
Ordinary and radiative muon capture on the proton and the pseudoscalar form factor of the nucleon
We calculate ordinary and radiative muon capture on the proton in an
effective field theory of pions, nucleons and delta isobars, working to third
and second order in the small scale expansion respectively. Preceding
calculations in chiral effective field theories only employed pion and nucleon
degrees of freedom and were not able to reproduce the photon spectrum in the
pioneering experiment of radiative muon capture on the proton from TRIUMF. For
the past few years it has been speculated that the discrepancy between theory
and experiment might be due to Delta(1232) related effects, which are only
included via higher order contact interactions in the standard chiral approach.
In this report we demonstrate that this speculation does not hold true. We show
that contrary to expectations from naive dimensional analysis isobar effects on
the photon spectrum and the total rate in radiative muon capture are of the
order of a few percent, consistent with earlier findings in a more
phenomenological approach. We further demonstrate that both ordinary and
radiative muon capture constitute systems with a very well behaved chiral
expansion, both in standard chiral perturbation theory and in the small scale
expansion, and present some new ideas that might be at the bottom of the still
unresolved discrepancy between theory and experiment in radiative muon capture.
Finally we comment upon the procedure employed by the TRIUMF group to extract
new information from their radiative muon capture experiment on the
pseudoscalar form factor of the nucleon. We show that it is inconsistent with
the ordinary muon capture data.Comment: 22 pp, RevTeX, uses epsf, 8 figs, enlarged version, discussion of
ordinary muon capture on protons substantially enlarged, accepted for
publication in Nucl.Phys.A, FZJ-IKP(TH)-2000-0
The Delta-resonance in a finite volume
We study the extraction of Delta-resonance parameters from lattice data for
small quark masses, corresponding to the case of an unstable Delta. To this
end, we calculate the spectrum of the correlator of two Delta-fields in a
finite Euclidian box up-to-and-including O(epsilon^3) in the small scale
expansion using infrared regularization. On the basis of our numerical study,
we argue that the extraction of the parameters of the Delta-resonance (in
particular, of the mass and the pion-nucleon-delta coupling constant) from the
measured volume dependence of the lowest energy levels should be feasible.Comment: 20 pages, 8 postscript figure
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