Summary
Deinococcus spp are among the most radiation‐resistant micro‐organisms that have been discovered. They show remarkable resistance to a range of damage caused by ionizing radiation, ...desiccation, UV radiation and oxidizing agents. Traditionally, Escherichia coli and Saccharomyces cerevisiae have been the two platforms of choice for engineering micro‐organisms for biotechnological applications, because they are well understood and easy to work with. However, in recent years, researchers have begun using Deinococcus spp in biotechnologies and bioremediation due to their specific ability to grow and express novel engineered functions. More recently, the sequencing of several Deinococcus spp and comparative genomic analysis have provided new insight into the potential of this genus. Features such as the accumulation of genes encoding cell cleaning systems that eliminate organic and inorganic cell toxic components are widespread among Deinococcus spp. Other features such as the ability to degrade and metabolize sugars and polymeric sugars make Deinococcus spp. an attractive alternative for use in industrial biotechnology.
In Erwinia chrysanthemi production of pectic enzymes is controlled by a complex network involving several regulators. Among them is ExpR, the quorum-sensing regulatory protein. ExpR is a member of ...the LuxR family of transcriptional regulators, the activity of which is modulated by the binding of diffusible N-acylhomoserine lactone pheromones to the N-terminal receptor site of the proteins. Previous in vitro DNA-ExpR binding studies suggested that ExpR might activate pectic enzyme production and repress its cognate gene expression. This report presents genetic evidence that ExpR represses its own gene expression in the absence of pheromone and that the addition of pheromone promotes concentration-dependent de-repression. In vitro experiments show that (i) ExpR binds target DNA in the absence of pheromone and that the pheromone dissociates ExpR-DNA complexes, (ii) ExpR binds target DNA in a non-cooperative fashion, and (iii) two molecules of pheromone are bound per molecule of ExpR dimer. In the absence of N-(3-oxo-hexanoyl)-homoserine lactone, ExpR prevents RNA polymerase access to the expR promoter, thereby directly repressing transcription initiation. The presence of pheromone renders the expR promoter accessible to RNA polymerase and results in the de-repression of transcription initiation. Overall we have established that there is a direct modulation of the repressive activity of a LuxR family regulator by a pheromone. Furthermore, site-directed mutagenesis experiments strongly suggest that the ExpR residues Leu-19, Tyr-31, and Ser-125 are involved in the transduction of conformational changes induced by ligand binding, and this provides new insights into the structure-function relationship of this bacterial regulator family.
▪A series of homoserine lactone derived ureas were synthesized and evaluated for their ability to inhibit the quorum sensing in
Vibrio fischeri bacteria.
A series of 15 racemic alkyl- and ...aryl-N-substituted ureas, derived from homoserine lactone, were synthesized and tested for their ability to competitively inhibit the action of 3-oxohexanoyl-
l-homoserine lactone, the natural inducer of bioluminescence in the bacterium
Vibrio fischeri.
N-alkyl ureas with an alkyl chain of at least 4 carbon atoms, as well as certain ureas bearing a phenyl group at the extremity of the alkyl chain, were found to be significant antagonists. In the case of
N-butyl urea, it has been shown that the antagonist activity was related to the inhibition of the dimerisation of the N-terminal domain of ExpR, a protein of the receptor LuxR family. Molecular modelling suggested that this would result from the formation of an additional hydrogen bond in the protein acylhomoserine lactone binding cavity.
The crystallographic structure of the family 3 polysaccharide lyase (PL-3) PelI from Erwinia chrysanthemi has been solved to 1.45Å resolution. It consists of an N-terminal domain harboring a ...fibronectin type III fold linked to a catalytic domain displaying a parallel β-helix topology. The N-terminal domain is located away from the active site and is not involved in the catalytic process. After secretion in planta, the two domains are separated by E. chrysanthemi proteases. This event turns on the hypersensitive response of the host. The structure of the single catalytic domain determined to 2.1Å resolution shows that the domain separation unveils a “Velcro”-like motif of asparagines, which might be recognized by a plant receptor. The structure of PelI in complex with its substrate, a tetragalacturonate, has been solved to 2.3Å resolution. The sugar binds from subsites -2 to +2 in one monomer of the asymmetric unit, although it lies on subsites -1 to +3 in the other. These two “Michaelis complexes” have never been observed simultaneously before and are consistent with the dual mode of bond cleavage in this substrate. The bound sugar adopts a mixed 21 and 31 helical conformation similar to that reported in inactive mutants from families PL-1 and PL-10. However, our study suggests that the catalytic base in PelI is not a conventional arginine but a lysine as proposed in family PL-9.
A series of 11 new analogues of N-acylhomoserine lactones in which the carboxamide bond was replaced by a sulfonamide one, has been synthesised. These compounds were evaluated for their ability to ...competitively inhibit the action of 3-oxohexanoyl-L-homoserine lactone, the natural ligand of the quorum sensing transcriptional regulator LuxR, which in turn activates expression of bioluminescence in the model bacterium Vibrio fischeri. Several compounds were found to display antagonist activity. Molecular modeling suggests that the latter prevent a cascade of structural rearrangements necessary for the formation of the active LuxR dimer.
The pectate lyase PelI is involved in the degradation of plant tissues by the phytopathogenic bacterium Erwinia chrysanthemi. It has been crystallized from a solution containing PEG 550 in the space ...group P21, with unit‐cell parameters a = 61.6, b = 70.7, c = 73.4 Å, β = 112.8°. Crystals diffract to 1.45 Å using synchrotron radiation. SAD phases have been computed from a gold‐derivative crystal at the wavelength of maximum absorption (LIII edge).
A series of 11 new analogues of N-acylhomoserine lactones in which the carboxamide bond was replaced by a sulfonamide one, has been synthesised. These compounds were evaluated for their ability to ...competitively inhibit the action of 3-oxohexanoyl-L-homoserine lactone, the natural ligand of the quorum sensing transcriptional regulator LuxR, which in turn activates expression of bioluminescence in the model bacterium Vibrio fischeri. Several compounds were found to display antagonist activity. Molecular modeling suggests that the latter prevent a cascade of structural rearrangements necessary for the formation of the active LuxR dimer.A series of 11 new analogues of N-acylhomoserine lactones in which the carboxamide bond was replaced by a sulfonamide one, has been synthesised. These compounds were evaluated for their ability to competitively inhibit the action of 3-oxohexanoyl-L-homoserine lactone, the natural ligand of the quorum sensing transcriptional regulator LuxR, which in turn activates expression of bioluminescence in the model bacterium Vibrio fischeri. Several compounds were found to display antagonist activity. Molecular modeling suggests that the latter prevent a cascade of structural rearrangements necessary for the formation of the active LuxR dimer.
This contribution is devoted to the study of the aerodynamic characteristics of non-spherical particles of definite regular shape, such as prolate and oblate ellipsoids as well as cylinders, immersed ...in a locally linear shear flow. The flow resistance coefficients of drag, lift and pitching torque are computed by means of the Particle Resolved Direct Numerical Simulation (PR-DNS) technique for such shapes as function of the Reynolds number Re. The parameter space comprises particle aspect ratio, AR, fluid spin ratio, ζ, and particle orientation angle, α. The Reynolds numbers of interest are in the intermediate range 1≤Re≤100, common in industrial and environmental processes. To properly understand and explain the obtained results, the role of the friction and pressure contributions to total flow coefficients is analyzed in detail for the different cases, allowing the differences between the considered shapes to be pointed out. On the other hand, the behavior of the pressure and skin friction coefficients in the particle plane of symmetry parallel to the flow is investigated as a function of the previous parameters (shape, AR, ζ, α), which provides further insights into the features of the shear flow around the non-spherical particles at finite Re. Finally, the influence of the shear flow magnitude and incidence angle on the location of the center of aerodynamic force is devised for the three shapes considered as function of Reynolds number and particle aspect ratio. It is expected that the information generated in this work will be useful for researchers to enhance the modeling of non-spherical particles immersed in non-uniform flows.
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•PR-DNS of simple shear flow around regular non-spherical particles.•Determination of drag, lift and torque on prolate, oblate ellipsoids & cylinders.•Effect of aspect ratio (AR), shear flow rate & Reynolds number on flow coefficients.•Effect of shear rate & AR on pressure and skin friction coefficients on the 3 shapes.•Effect of shear rate and aspect ratio on center of force location.
Members of the histone-like nucleoid-structuring (H-NS) family of proteins have been shown to play important roles in silencing gene expression and in nucleoid compaction. In Pseudomonas aeruginosa, ...the two H-NS family members MvaT and MvaU are thought to bind the same AT-rich regions of the chromosome and function coordinately to control a common set of genes. Here we present evidence that the loss of both MvaT and MvaU cannot be tolerated because it results in the production of Pf4 phage that superinfect and kill cells or inhibit their growth. Using a ClpXP-based protein depletion system in combination with transposon mutagenesis, we identify mutants of P. aeruginosa that can tolerate the depletion of MvaT in an ΔmvaU mutant background. Many of these mutants contain insertions in genes encoding components, assembly factors, or regulators of type IV pili or contain insertions in genes of the prophage Pf4. We demonstrate that cells that no longer produce type IV pili or that no longer produce the replicative form of the Pf4 genome can tolerate the loss of both MvaT and MvaU. Furthermore, we show that the loss of both MvaT and MvaU results in an increase in expression of Pf4 genes and that cells that cannot produce type IV pili are resistant to infection by Pf4 phage. Our findings suggest that type IV pili are the receptors for Pf4 phage and that the essential activities of MvaT and MvaU are to repress the expression of Pf4 genes.
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