Structures of the N-Terminal Domain of PqsA in Complex with Anthraniloyl- and 6-Fluoroanthraniloyl-AMP: Substrate Activation in Pseudomonas Quinolone Signal (PQS) Biosynthesis

Pseudomonas aeruginosa, a prevalent pathogen in nosocomial infections and a major burden in cystic fibrosis, uses three interconnected quorum-sensing systems to coordinate virulence processes. At variance with other Gram-negative bacteria, one of these systems relies on 2-alkyl-4(1H)-quinolones (Pseudomonas quinolone signal, PQS) and might hence be an attractive target for new anti-infective agents. Here we report crystal structures of the N-terminal domain of anthranilate-CoA ligase PqsA, the first enzyme of PQS biosynthesis, in complex with anthraniloyl-AMP and with 6-fluoroanthraniloyl-AMP (6FABA-AMP) at 1.4 and 1.7 Å resolution. We find that PqsA belongs to an unrecognized subfamily of anthranilate-CoA ligases that recognize the amino group of anthranilate through a water-mediated hydrogen bond. The complex with 6FABA-AMP explains why 6FABA, an inhibitor of PQS biosynthesis, is a good substrate of PqsA. Together, our data might pave a way to new pathoblockers in P. aeruginosa infections.     

Modelling of solid formation by heterogeneous reactions through a multicomponent transport model of diluted ionic species: Simulation of barite fouling in a geothermal heat exchanger

A general model is proposed in order to describe the growth of a deposit by heterogeneous reactions. The hydrodynamics in the fluid is described by a multicomponent transport model for ionic species diluted in a solvent and heat transfer is taken into account in both liquid and solid domains. The boundary condition at the interface where the reaction takes place is described thoroughly. It involves the reaction kinetics and gives access to the velocity of the interface, ie, the mass rate of the solid deposit. The model is then applied to the case of barite crystallization in a heat exchanger. The liquid phase is therefore composed of two ionic species Ba²⁺ and SO₄²⁻ diluted in water. The solid phase is modelled as a homogeneous barite deposit. The fully dynamic CFD simulation of the model is made using Comsol Multiphysics, in a cylindrical pipe. The solid growth is analyzed over time and space in terms of the relevant variables of the model.     

Cuticular hydrocarbons of Tetramorium ants from central Europe: analysis of GC-MS data with self-organizing maps (SOM) and implications for systematics

Cuticular hydrocarbons were extracted from workers of 63 different nests of five species of Tetramorium ants (Hymenoptera: Formicidae) from Austria, Hungary, and Spain. The GC-MS data were classified (data mining) by self-organizing maps (SOM). SOM neurons derived from primary neuron separation were subjected to hierarchical SOM (HSOM) and were grouped to neuron areas on the basis of vicinity in the hexagonal output grid. While primary neuron separation and HSOM resulted in classifications on a level more sensitive than species differences, neuron areas resulted in chemical phenotypes apparently of the order of species. These chemical phenotypes have implications for systematics: while the chemical phenotypes for T. ferox and T. moravicum correspond to morphological determination, in T. caespitum and T. impurum a total of six chemical phenotypes is found. Three hypotheses are discussed to explain this disparity between morphological and chemical classifications, including in particular the possibility of hybridization and the existence of cryptic species. Overall, the GC-MS profiles classified by SOM prove to be a practical alternative to morphological determination (T. ferox, T. moravicum) and indicate the need to revisit systematics (T. caespitum, T. impurum).     

Nocturnal Plant Bugs Use <Emphasis Type="Italic">cis</Emphasis>-Jasmone to Locate Inflorescences of an Araceae as Feeding and Mating Site

Inflorescences of Araceae pollinated by cyclocephaline scarab beetles are visited frequently by a wide array of other arthropods that exploit floral resources without taking part in pollination, including earwigs, flies, and true bugs. To date, nothing is known about the cues these insect visitors use to locate the inflorescences and whether or to what extent floral scents play a role. An aroid visited by large numbers of plant bugs (Miridae) in addition to cyclocephaline scarab beetle pollinators is the Neotropical species Dieffenbachia aurantiaca. We identified the plant bug species and investigated their behavior and arrival time on the inflorescences. To test the importance of olfactory cues in locating their host we conducted experiments with open and gauze-bagged inflorescences as well as natural scent samples of D. aurantiaca. Inflorescence scents were analyzed by gas chromatography linked to mass spectrometry (GC/MS), and the attractive potential of the main scent compound was determined by behavioral assays. Three species of Neella, the most common one being N. floridula, visited the inflorescences at nightfall, shortly after the beginning of scent emission, and showed feeding and copulation activity. Bagged inflorescences as well as natural scent samples attracted similar numbers of plant bugs as the non-bagged inflorescences, showing that olfactory cues are sufficient for them to locate their host. Cis-jasmone was the major component within the inflorescence scent bouquet. In two-choice field bioassays, this compound proved to be highly attractive to Neella, and thus obviously plays a key role in finding host plants.     

Homoserine Lactones,Methyl Oligohydroxybutyrates,and Other Extracellular Metabolites of Macroalgae‐Associated Bacteria of the Roseobacter Clade: Identification and Functions

Twenty‐four strains of marine Roseobacter clade bacteria were isolated from macroalgae and investigated for the production of quorum‐sensing autoinducers, N‐acylhomoserine lactones (AHLs). GC/MS analysis of the extracellular metabolites allowed us to evaluate the release of other small molecules as well. Nineteen strains produced AHLs, ranging from 3‐OH‐C10:0‐HSL (homoserine lactone) to (2E,11Z)‐C18:2‐HSL, but no specific phylogenetic or ecological pattern of individual AHL occurrence was observed when cluster analysis was performed. Other identified compounds included indole, tropone, methyl esters of oligomers of 3‐hydroxybutyric acid, and various amides, such as N‐9‐hexadecenoylalanine methyl ester (9‐C16:1‐NAME), a structural analogue of AHLs. Several compounds were tested for their antibacterial and antialgal activity on marine isolates likely to occur in the habitat of the macroalgae. Both AHLs and 9‐C16:1‐NAME showed high antialgal activity against Skeletonema costatum, whereas their antibacterial activity was low.     

Temperature Stability of Lead‐Free Niobate Piezoceramics with Engineered Morphotropic Phase Boundary

The temperature dependence of piezoelectric properties (direct piezoelectric coefficient d₃₃, converse piezoelectric coefficient d₃₃(E = 0), strain S and electromechanical coupling coefficient k_p) for two niobate‐based lead‐free piezoceramics have been contrasted. 0.92(Na_0.5K_0.5)NbO₃–0.02(Bi_1/2Li_1/2)TiO₃–0.06BaZrO₃ (6BZ/2BLT/92NKN) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at room temperature and 0.92(Na_0.5K_0.5)NbO₃–0.03(Bi_1/2Li_1/2)TiO₃–0.05BaZrO₃ (5BZ/3BLT/92NKN) features an MPB engineered to be located below room temperature. At 30°C, d₃₃, d₃₃(E = 0), S (at 2 kV/mm), and k_p are 252 pC/N, 230 pm/V, 0.069%, 0.51 for 5BZ/3BLT/92NKN; and 348 pC/N, 380 pm/V, 0.106%, 0.57 for 6BZ/2BLT/92NKN, respectively. With increasing temperature, the piezoelectric properties decrease. At 200°C, d₃₃, d₃₃(E = 0), S (at 2 kV/mm), and k_p are 170 pC/N, 160 pm/V, 0.059%, 0.36 for 5BZ/3BLT/92NKN; and 181 pC/N, 190 pm/V, 0.061%, 0.39 for 6BZ/2BLT/92NKN. It is found that the electromechanical coupling coefficient has a better temperature stability than the piezoelectric coefficient in the studied system due to a large temperature‐dependent compliance change. The results demonstrate that engineering an MPB is highly effective in tailoring temperature stability of piezoceramics.     

Mutation of Conserved Residues Increases in Vitro Activity of the Formylglycine‐Generating Enzyme

The formylglycine‐generating enzyme (FGE) recognizes proteins with a specific cysteine‐containing six‐amino‐acid motif and converts this cysteine residue into formylglycine. The resulting aldehyde function provides a unique handle for selective protein labeling. We have identified two mutations in FGE from Thermomonospora curvata that increase this catalytic efficiency more than 40‐fold. The resulting activity and stability, as well as its ease of recombinant production, make this FGE variant a practical reagent for in vitro protein engineering.