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The discovery that plant smoke contains germination stimuli has led to the identification of a new class of signaling molecules named karrikins. Here we report a potential second role for these molecules: in various bacterial species – A. tumefaciens, P. aeruginosa and V. harveyi – they modulate bacterial quorum-sensing (QS), with very different outcomes.

Live cell fluorescent labeling of proteins has become a seminal tool in biology and has led to hallmark discoveries in diverse research areas such as protein trafficking, cell-to-cell interactions, and intracellular network dynamics. One of the main challenges, however, remains the ability to label intracellular proteins using fluorescent ligands with high specificity, all the while retaining viability of the targeted cells. Here, we present the first example of live cell labeling and imaging of an intracellular bacterial receptor involved in cell-to-cell communication (i.e., quorum sensing), using a novel two-step approach involving covalent attachment of a reactive mimic of the primary endogenous Pseudomonas aeruginosa quorum-sensing signal to its receptor, LasR, followed by aniline-catalyzed oxime formation between the modified receptor and a fluorescent BODIPY derivative. Our results indicate that LasR is not distributed evenly throughout the cytoplasmic membrane but is instead concentrated at the poles of the P. aeruginosa cell.

Chemical coordination of gene expression among bacteria as a function of population density is regulated by a mechanism known as 'quorum sensing' (QS). QS in Pseudomonas aeruginosa, an opportunistic pathogen that causes disease in immunocompromised patients, is mediated by binding of the transcriptional activator, LasR, to its ligand, 3-oxo-C(12)-HSL, leading to population-wide secretion of virulence factors and biofilm formation. We have targeted QS in P. aeruginosa with a set of electrophilic probes designed to covalently bind Cys79 in the LasR binding pocket, leading to specific inhibition of QS-regulated gene expression and concomitant reduction of virulence factor secretion and biofilm formation. This first example of covalent modification of a QS receptor provides a new tool to study molecular mechanisms of bacterial group behavior and could lead to new strategies for targeting bacterial virulence.

Efficient syntheses, X-ray structures and spectroscopic properties of s-indacene-1,3,5,7(2H,6H)-tetraone (1) and 1,3-dioxo-5,6-indanedicarboxylic acid (2), their precursors and derivatives, are described for the first time.

The synthesis and evaluation of a 'tag-free' probe to isolate and identify receptors for N-acyl homoserine lactones is described.

The synthesis and comparison of activities of ‘tag-free’ probes with diazirines at various positions are described. Remarkable differences in their effects on P. aeruginosa and on human bronchial epithelial cells were observed, supporting the efforts to isolate and identify receptors for N-acyl homoserine lactones.

The longest wave absorption band of the tetramethylthio- tetrathiafulvalene cation radical, which is usually interpreted as a π-dimer band, is shown to be the intrinsic cation radical absorption, all studied cation radicals in solution at room temperature exist as paramagnetic monomers and only tetrathiafulvelene and tetramethyltetrathiafulvalene cation radicals undergo π-dimerization at low temperatures.

A one-step label-free electrochemical assay for quorum sensing inhibition in Pseudomonas aeruginosa is presented.

We studied Langmuir and Langmuir–Blodgett (LB) films of several strong nonlinear optical (NLO) active amphiphilic derivatives of 1,3-indanedione-5,6-dicarboxylic acid. The surface pressure–area (π–A) isotherms at the air–water interface were investigated at different temperatures and pH values. Non-centrosymmetric Z-type LB films were deposited. UV–visible spectra indicated a uniform film transfer. The orientation of the molecular transition moments was calculated from the polarized UV–visible spectra. Packing within the LB films was observed by UV–visible absorption and fluorescence spectroscopy. The morphology of the LB films was examined by AFM and compared to ellipsometric measurements, and the nature of the films was studied by contact angle measurements. Significant second harmonic generation (SHG) by the LB films was observed. Alternate layer Y-type LB films of two different dyes were fabricated to achieve enhanced stability and SHG.