Identification of boronic acids as antagonists of bacterial quorum sensing in Vibrio harveyi

Bacterial quorum sensing plays a very important role in the regulation of biofilm formation, virulence, conjugation, sporulation, and swarming mobility. Inhibitors of bacterial quorum sensing are important research tools and potential therapeutic agents. In this paper, we describe for the first time the discovery of several boronic acids as single digit micromolar inhibitors of bacterial quorum sensing in Vibrio harveyi.     

Displacement of sterols from sterol/sphingomyelin domains in fluid bilayer membranes by competing molecules

The formation of sterol and palmitoyl sphingomyelin enriched ordered domains in a fluid bilayer was examined using domain selective fluorescent reporter molecules (cholestatrienol and trans-parinaric acid containing lipids) together with a quencher molecule in the fluid phase. The aim of the study was to explore how stable the ordered domains were and how different, biologically interesting, membrane intercalators could affect domain stability and sterol distribution between domains. We show that sterols easily can be displaced from ordered domains by a variety of saturated, single- and double-chain membrane intercalators with a small polar group as a common denominator. Of the two-chain intercalators examined, both palmitoyl ceramide and palmitoyl dihydroceramide were effective in displacing sterols from ordered domains. Of the single-chain intercalators, hexadecanol and hexadecyl amide displaced the sterol from sterol/sphingomyelin domains, whereas palmitic acid, sphingosine and sphinganine failed to do so. All molecules examined stabilized the sphingomyelin-rich domains, as reported by trans-parinaric-sphingomyelin and by scanning calorimetry. Parallels between the displacement of sterol from ordered domains in our model membrane system and the ability of the above mentioned molecules to alter the chemical activity and distribution of sterols in biological membranes are discussed.     

Anti-quorum sensing and anti-biofilm activity of Amomum tsaoko (Amommum tsao-ko Crevost et Lemarie) on foodborne pathogens

Cell-to-cell communication or quorum sensing (QS) leads to biofilm formation and causing other virulence factors which are extreme problems for food safety, biofilm related infectious diseases etc. This study evaluated the anti-QS activity of the Amomum tsaoko extract (0.5–4 mg/ml) by using Chromobacterium violaceum a biosensor strain and biofilm formation by crystal violate assay. Experimental results demonstrated that the overall yield of Amomum tsao-ko extract was 11.33 ± 0.3% (w/w). MIC for Staphylococcus aureus (Gram positive), Salmonella Typhimurium and Pseudomonas aeruginosa (Gram negative) was 1, 2 and 2 mg/ml, respectively. A concentration of 4 mg/ml extract showed highest biofilm inhibition 51.96% on S. Typhimurium when 47.06%, 45.28% were shown by S. aureus, P. aeruginosa respectively. The damage of biofilm architecture was observed by Confocal Laser Scanning Microscopy (CLSM). A level of 44.59% inhibition of violacein production was demonstrated when the dose was 4 mg/ml. Swarming motility inhibition was observed in a dose dependent manner. Taken together, the treatment of A. tsaoko extract can deliver value to food product and medicine by controlling pathogenesis.     

Gac two-component system in Pseudomonas syringae pv. tabaci is required for virulence but not for hypersensitive reaction

Pseudomonas syringae pv. tabaci 6605 causes wildfire disease on host tobacco plants. To investigate the regulatory mechanism of the expression of virulence, Gac two-component system-defective mutants, ΔgacA and ΔgacS, and a double mutant, ΔgacAΔgacS, were generated. These mutants produced smaller amounts of N-acyl homoserine lactones required for quorum sensing, had lost swarming motility, and had reduced expression of virulence-related hrp genes and the algT gene required for exopolysaccharide production. The ability of the mutants to cause disease symptoms in their host tobacco plant was remarkably reduced, while they retained the ability to induce hypersensitive reaction (HR) in the nonhost plants. These results indicated that the Gac two-component system of P. syringae pv. tabaci 6605 is indispensable for virulence on the host plant, but not for HR induction in the nonhost plants. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. The nucleotide sequence data reported in this paper have been submitted to the DDBJ/GenBank/EMBL databank with the accession numbers AB266103, AB266104, AB266105, AB266106, AB266107, AB266108.     

A single mutation in P450BM-3 enhances acyl homoserine lactone: acyl homoserine substrate binding selectivity nearly 250-fold

Quorum sensing is the process by which bacteria alter gene regulation in response to their population density. The enzymatic inactivation of quorum signals has shown promise for use in genetically modified organisms resistant to pathogens. We recently characterized the ability of a cytochrome P450, P450BM-3, to oxidize the quorum sensing signals known as acyl homoserine lactones. The oxidation of the acyl homoserine lactones reduced their activity as quorum signals. The enzyme also oxidized the inactive lactonolysis products, acyl homoserines. The enzyme showed similar binding affinity for the acyl homoserine lactones and acyl homoserines. The latter reaction may lead to problems when lactonases and the P450-dependent system are used in tandem, as oxidation of the acyl homoserines produced by lactonolysis in vivo may compete with acyl homoserine lactone oxidation by the cytochrome P450. We report here that a single mutation (R47S) in P450BM-3 is capable of increasing the acyl homoserine lactone: acyl homoserine substrate binding selectivity of the enzyme nearly 250-fold, reducing the potential for competition by acyl homoserines and significantly enhancing the potential for use of P450BM-3 as part of a pathogen resistance system in genetically modified crops.     

Identifying ‘prime suspects’: symbioses and the evolution of multicellularity

The possible involvement of symbioses in the evolution of multicellularity is explored. Evidence is drawn principally from the biology of present day associations of plants and animals with prokaryotes. A particular emphasis is placed on future research opportunities in this area of biology that have been provided by the advent of specific molecular techniques and new model systems. With the application of new approaches that result from these advances, a more holistic understanding of the biology of the coevolved communities, composed of animals or plants and their associated prokaryotes, is within the reach of biologists over the next few decades.