Cation effect on energy transfer reactions from [Tb(2,6-pyridinedicarboxylate)3] to anionic chromium(III) and neodymium(III) complexes in aqueous solutions

Cation effects are studied on the excitation energy transfer reaction between anionic complexes, i.e., [Tb(dpa)₃]³⁻ (dpa=2,6-pyridinedicarboxylate) quenched by [Cr(ox)₃]³⁻ (ox=oxalate ion), [Cr(mal)₃]³⁻ (mal=malonate ion) and [Nd(dpa)₃]³⁻ in aqueous solutions in the presence of alkali metal ions added for adjustments of ionic strengths. In the quenching reaction of [Cr(ox)₃]³⁻, magnitudes of quenching rate constants (k_q) and energy transfer rate constant in encounter complex (k₁) are changed by the cations in the order of Li⁺ < Na⁺ < K⁺ ≈ Rb⁺ ≈ Cs⁺, that is quite contrary of the cation effect on energy transfer reaction between [Ru(N-N)₃]²⁺ and [Cr(ox)₃]³⁻, reported in the previous paper. On the other hand, the rate constants in quenching reactions by [Cr(mal)₃]³⁻ and [Nd(dpa)₃]³⁻ remain almost constant. This result indicates that more separated donor-acceptor pair is not sensitive to coexisting cations.     

Sensitivity of the quorum sensing system is achieved by low pass filtering

Autoinducer sensing, also known as quorum sensing, is the communication of bacteria by autoinducer (small signaling molecules). Cells respond on extremely low concentrations of autoinducer: only one or two molecules per cell are sufficient. At this signal level a high degree of noise is inherent. We ask for the mechanism that is able to overcome the stochasticity of the signal. By means of a model and parameter fitting we show that the sensing module acts as a low pass filter, representing the biochemical equivalent of a moving average. It is shown that the system works most sensitive in the range of 0-50 nM autoinducer. Moreover, the time scale of the reaction depends on the signal strength in a crucial manner. Nonlinear feedback is able to further enhance the sensitivity. The biological implications of the low pass filter property are discussed.     

Antagonistic effect of divalent cations Ca<Superscript>2+</Superscript> and Mg<Superscript>2+</Superscript> on the morphological development of <Emphasis Type="Italic">Streptomyces hygroscopicus</Emphasis> var. <Emphasis Type="Italic">geldanus</Emphasis>

The automated docking program DOCK 5.3.0 was applied to screening for quorum sensing inhibitors (QSIs) of Peudomonus aeruginosa from a database containing 51 active components of Traditional Chinese Medicines with antibacterial activity. Five potential QSIs were revealed by the computer-based virtual screening. The compounds 3, 4, 5, 6, 7 inhibit biofilm formation of P. aeruginosa at a concentration of 200 μM. Compound 4 (baicalein) does not inhibit the growth of P. aeruginosa; however, it significantly inhibits biofilm formation of the bacteria at a lower concentration of 20 μM and promoted proteolysis of the signal receptor TraR protein in Escherichia coli at 4–40 mM. Baicalein and ampicillin showed synergistic activity against P. aeruginosa. These results suggested that baicalein can interfere with quorum sensing system of P. aeruginosa and will be developed as antibacterial agent with novel target.     

Interplay of two quorum sensing regulation systems of Vibrio fischeri

Many bacteria developed a possibility to recognise aspects of their environment or to communicate with each other by chemical signals. An important strategy is the so-called quorum sensing (QS), a regulatory mechanism for the gene expression, where the bacteria measure their own cell density by means of this signalling pathway. One of the best-studied species using QS is the marine luminescent bacterium Vibrio fischeri which is considered here as a model organism.The two main regulatory pathways (lux and ain) are combined to a regulation system, the dynamics is modelled by an ODE system. This system is analysed thoroughly, considering stationary states, dynamical behaviour and the possible biological meaning of it. The influence of different parameter values on the behaviour is examined, the same basic system is able to reflect the peculiarities of different bacteria strains (respectively, their mutants).     

Development of a novel series of non-natural triaryl agonists and antagonists of the Pseudomonas aeruginosa LasR quorum sensing receptor

Bacterial chemical communication, through a process called quorum sensing (QS), plays a central role in infection in numerous bacterial pathogens. Quorum sensing in Pseudomonas aeruginosa employs a series of small molecule receptors including the master QS regulator, LasR. In this study we investigate a non-natural triaryl series of LasR ligands using a combination of structure activity relationship studies and computational modeling. These studies have enabled the identification of key structural requirements for ligand binding and have revealed a new strategy for inducing the therapeutically relevant antagonism of LasR.     

Quorum quenching enzyme activity is widely conserved in the sera of mammalian species

Acyl-homoserine lactone (AHL) quorum sensing signals play a key role in synchronizing virulence gene expression in Pseudomonas aeruginosa, which could cause fatal bloodstream infections. We showed that AHL inactivation activity, albeit with variable efficiency, was conserved in the serum samples of all the 6 tested mammalian animals. High-performance liquid chromatography and mass spectrometry analyses revealed that mammalian sera had a lactonase-like enzyme(s), which hydrolyzed the lactone ring of AHL to produce acyl homoserine, with enzyme properties reminiscent of paraoxonases (PONs). We further showed that the animal cell lines expressing three mouse PON genes, respectively, displayed strong AHL degradation activities.     

Impact of the cold shock phenomenon on quantification of intracellular metabolites in bacteria

In the present work the effect of quenching on quantification of intracellular metabolites in Corynebacterium glutamicum was investigated. C. glutamicum showed a high sensitivity to cold shock. Quenching of the cells by -50 degrees C buffered methanol prior to cell separation and extraction led to drastically reduced concentrations for free intracellular amino acids compared to those for nonquenched filtration. As demonstrated for glutamate and glutamine, this was clearly due to a more than 90% loss of these compounds from the cell interior into the medium during quenching. With lower methanol concentration in the quenching solution the metabolic losses were significantly lower but still amounted to about 30%. Due to the fact that quenching with ice-cold NaCl (0.9%) also resulted in significantly lower pool sizes for intracellular amino acids, a basic cold shock phenomenon is most likely the reason for the observed effects. The results clearly demonstrate that quenching combined with cell separation for concentration of the cells and removal of the medium is not applicable for intracellular metabolite analysis in C. glutamicum. Sampling by quick filtration without quenching allows complete cell separation and authentic quantification of intracellular metabolite pools exhibiting time constants significantly larger than sampling time.