Identification of N-acylhomoserine lactones in mucopurulent respiratory secretions from cystic fibrosis patients

Pseudomonas aeruginosa and species of the Burkholderia cepacia complex are the primary bacterial pathogens contributing to lung disease in patients with cystic fibrosis. Quorum sensing systems using N-acyl homoserine lactone (AHL) signal molecules are involved in the regulation of a number of virulence factors in these species. Extracts of mucopurulent respiratory secretions from 13 cystic fibrosis patients infected with P. aeruginosa and/or strains of the B. cepacia complex were fractionated using reverse-phase fast pressure liquid chromatography and analyzed for the presence of AHLs using a traI-luxCDABE-based reporter that responds to AHLs with acyl chains ranging between 4 and 12 carbons. Using this assay system, a broad range of AHLs were detected and identified despite being present at low concentrations in limited sample volumes. N-(3-oxo-dodecanoyl)-l-homoserine lactone, N-(3-oxo-decanoyl)-l-homoserine lactone and N-octanoyl-l-homoserine lactone (OHL) were the AHLs most frequently identified. OHL and N-decanoyl-l-homoserine lactone were detected in nanomolar concentrations compared to picomolar amounts of the 3-oxo-derivatives of the AHLs identified.     

Changes of serum albumin affinity for aspirin induced by fatty acid

Saturated fatty acids such as myristic acid play an important role in the pathogenesis of cardiovascular disorders.

Using the quenching fluorescence method we examined the influence of myristate on the changes of transporting protein affinity towards aspirin—the most popular anticoagulant.

Our results showed that the presence of the myristic acid alters the stability of the anticoagulant–albumin complex. The ranges of [myristate]/[albumin] molar ratio at which the stability of drug–protein complex increases or decreases were determined. The differences in interaction between ligands and human or bovine serum albumins were identified. The competition in binding of ligands with these albumins was also described.     

Photoinduced electron transfer and energy transfer reactions of hydroxo-(2,2′:6′,2″-terpyridine) platinum(II)

The luminescent complex [Pt(terpy)OH]BF₄ undergoes photoinduced electron transfer reactions with phenyl amine electron donors and nitrophenyl electron acceptors. Stern-Volmer analysis of the quenching of metal-to-ligand charge transfer phosphorescence (³MLCT) was used to calculate bimolecular rate constants for electron transfer. Rate constants vary from 10⁸ to >10¹⁰ M⁻¹ s⁻¹, depending on the thermodynamic driving force of the electron transfer reaction, with rate constants indicating that [Pt(terpy)OH]BF₄* is a powerful photo-oxidant. Aromatic triplet energy acceptors can also quench the ³MLCT emission.     

Structural Determinants Underlying Photoprotection in the Photoactive Orange Carotenoid Protein of Cyanobacteria

The photoprotective processes of photosynthetic organisms involve the dissipation of excess absorbed light energy as heat. Photoprotection in cyanobacteria is mechanistically distinct from that in plants; it involves the orange carotenoid protein (OCP), a water-soluble protein containing a single carotenoid. The OCP is a new member of the family of blue light-photoactive proteins; blue-green light triggers the OCP-mediated photoprotective response. Here we report structural and functional characterization of the wild type and two mutant forms of the OCP, from the model organism Synechocystis PCC6803. The structural analysis provides high resolution detail of the carotenoid-protein interactions that underlie the optical properties of the OCP, unique among carotenoid-proteins in binding a single pigment per polypeptide chain. Collectively, these data implicate several key amino acids in the function of the OCP and reveal that the photoconversion and photoprotective responses of the OCP to blue-green light can be decoupled.     

密度感应系统：对细菌致病力的自行调控

细菌通过密度感应系统感受环境中的信号分子,进而调控菌群一系列生物学性状。研究发现密度感应系统能够调控细菌生物被膜形成、毒力基因表达及噬菌体感染等功能,其中基于密度感应系统调控细菌抵御噬菌体感染更是新发现,预期也将是未来数年的研究热点,其调控机制的阐明将为有效应用噬菌体开展耐药菌的防控展现广阔前景。本文将重点综述细菌密度感应系统对细菌致病相关功能的调控机制,旨在为病原菌的防控提供新思路。     

Chemical identification of<Emphasis Type="Italic"> N</Emphasis>-acyl homoserine lactone quorum-sensing signals produced by<Emphasis Type="Italic"> Sinorhizobium meliloti</Emphasis> strains in defined medium

The N-acyl homoserine lactone (AHL) quorum-sensing signals produced by Sinorhizobium meliloti strains AK631 and 1021 when cultured in a defined glucose-nitrate medium were identified by gas chromatography/mass spectrometry (GC/MS) and electrospray ionization tandem mass spectrometry (ESI MS/MS). Both strains synthesized several long-chain AHLs. Defined medium cultures of strain AK631 synthesized a complex mixture of AHLs with short acyl side chains. Strain 1021 produced no short-chain AHLs when grown on defined medium and made a somewhat different set of long-chain AHLs than previously reported for cultures in rich medium. While the two strains produced several AHLs in common, the differences in AHLs produced suggest that there may be significant differences in their patterns of quorum-sensing regulation.     

Quenching in Arabidopsis thaliana mutants lacking monomeric antenna proteins of photosystem II

The minor light-harvesting complexes CP24, CP26, and CP29 have been proposed to play a key role in the zeaxanthin (Zx)-dependent high light-induced regulation (NPQ) of excitation energy in higher plants. To characterize the detailed roles of these minor complexes in NPQ and to determine their specific quenching effects we have studied the ultrafast fluorescence kinetics in knockout (ko) mutants koCP26, koCP29, and the double mutant koCP24/CP26. The data provide detailed insight into the quenching processes and the reorganization of the Photosystem (PS) II supercomplex under quenching conditions. All genotypes showed two NPQ quenching sites. Quenching site Q1 is formed by a light-induced functional detachment of parts of the PSII supercomplex and a pronounced quenching of the detached antenna parts. The antenna remaining bound to the PSII core was also quenched substantially in all genotypes under NPQ conditions (quenching site Q2) as compared with the dark-adapted state. The latter quenching was about equally strong in koCP26 and the koCP24/CP26 mutants as in the WT. Q2 quenching was substantially reduced, however, in koCP29 mutants suggesting a key role for CP29 in the total NPQ. The observed quenching effects in the knockout mutants are complicated by the fact that other minor antenna complexes do compensate in part for the lack of the CP24 and/or CP29 complexes. Their lack also causes some LHCII dissociation already in the dark.     

Heterometallic complex formation on p-sulfonatothiacalix[4]arene platform resulting in pH- and redox-modification of [Ru(bpy)3] luminescence

The pH-dependent heterometallic complex formation with p-sulfonatothiacalix[4]arene (TCAS) as bridging ligand in aqueous solutions was revealed by the use of spectrophotometry, nuclear magnetic relaxation and fluorimetry methods. The novelty of the structural motif presented is that the appendance of emission metal center ([Ru(bpy)₃]²⁺) is achieved through the cooperative non-covalent interactions with the upper rim of TCAS. The second metal block (Fe(III), Fe(II) and Mn(II)), bound with the lower rim of TCAS in the inner sphere coordination mode is serving as quencher of [Ru(bpy)₃]²⁺ emission. The difference between the complex ability of Fe(III) and Fe(II) ions provides pH conditions for redox-dependent emission of [Ru(bpy)₃]²⁺.     

Biofilm-induced modifications in the proteome of Pseudomonas aeruginosa planktonic cells

While recent studies focused on Quorum Sensing (QS) role in the cell-to-cell communication in free or biofilm cultures, no work has been devoted up to now to investigate the communication between sessile and planktonic bacteria. In this aim, we elaborated an original two-chambered bioreactor and used a proteomic approach to study the alterations induced by Pseudomonas aeruginosa biofilm cells on protein expression in planktonic counterparts (named SIPs for Surface-Influenced Planktonics). Proteomic analyses revealed the existence of 31 proteins whose amount varied in SIPs, among which five corresponded to hypothetic proteins and two (the Fur and BCP proteins) are involved in bacterial response to oxidative stress. An increase in the concentration of C₄-HSL (rhlR–rhlI-dependent QS) and 3-oxo-C₁₂-HSL (lasR–lasI-dependent QS) autoinducer molecules was shown in the planktonic compartment. Interestingly, among proteins that were accumulated by SIPs was 3-oxoacyl-[acyl-carrier-protein] reductase, a protein involved in the production of the autoinducer 3-oxo-C₁₂-HSL. These results demonstrate that planktonic organisms are able to detect the presence of a biofilm in their close environment and to modify their gene expression in consequence.