Effects of natural and chemically synthesized furanones on quorum sensing in Chromobacterium violaceum

BACKGROUND: Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such as the N-acylhomoserine lactones (AHL). These compounds are involved in the production of antibiotics, exoenzymes, virulence factors and biofilm formation. They belong to the class of furanone derivatives which are frequently found in nature as pheromones, flavor compounds or secondary metabolites. To obtain more information on the relation between molecular structure and quorum sensing, we tested a variety of natural and chemically synthesized furanones for their ability to interfere with the quorum sensing mechanism using a quantitative bioassay with Chromobacterium violaceum CV026 for antagonistic and agonistic action. We were looking at the following questions: 1. Do these compounds affect growth? 2) Do these compounds activate the quorum sensing system of C. violaceum CV026? 3) Do these compounds inhibit violacein formation induced by the addition of the natural inducer N-hexanoylhomoserine lactone (HHL)? 4) Do these compounds enhance violacein formation in presence of HHL? RESULTS: The naturally produced N-acylhomoserine lactones showed a strong non-linear concentration dependent influence on violacein production in C. violaceum with a maximum at 3.7*10(-8 )M with HHL. Apart from the N-acylhomoserine lactones only one furanone (emoxyfurane) was found to simulate N-acylhomoserine lactone activity and induce violacein formation. The most effective substances acting negatively both on growth and quorum sensing were analogs and intermediates in synthesis of the butenolides from Streptomyces antibioticus. CONCLUSION: As the regulation of many bacterial processes is governed by quorum sensing systems, the finding of natural and synthetic furanones acting as agonists or antagonists suggests an interesting tool to control and handle detrimental AHL induced effects. Some effects are due to general toxicity; others are explained by a competitive interaction for LuxR proteins. For further experiments it is important to be aware of the fact that quorum sensing active compounds have non-linear effects. Inducers can act as inhibitors and inhibitors might be able to activate or enhance the quorum sensing system depending on chemical structure and concentration levels

Streptomyces‐derived quorum‐sensing systems engineered for adjustable transgene expression in mammalian cells and mice

Prokaryotic transcriptional regulatory elements have been adopted for controlled expression of cloned genes in mammalian cells and animals, the cornerstone for gene‐function correlations, drug discovery, biopharmaceutical manufacturing as well as advanced gene therapy and tissue engineering. Many prokaryotes have evolved specific molecular communication systems known as quorum‐sensing to coordinate population‐wide responses to physiological and/or physicochemical signals. A generic bacterial quorum‐sensing system is based on a diffusible signal molecule that prevents binding of a repressor to corresponding operator sites thus resulting in derepression of a target regulon. In Streptomyces, a family of butyrolactones and their corresponding receptor proteins, serve as quorum‐sensing systems that control morphological development and antibiotic biosynthesis. Fusion of the Streptomyces coelicolor quorum‐sensing receptor (ScbR) to a eukaryotic transactivation domain (VP16) created a mammalian transactivator (SCA) which binds and adjusts transcription from chimeric promoters containing an SCA‐specific operator module (PSPA). Expression of erythropoietin or the human secreted alkaline phosphatase (SEAP) by this quorum‐sensor‐regulated gene expression system (QuoRex) could be fine‐tuned by non‐toxic butyrolactones in a variety of mammalian cells including human primary and mouse embryonic stem cells. Following intraperitoneal implantation of microencapsulated Chinese hamster ovary cells transgenic for QuoRex‐controlled SEAP expression into mice, the serum levels of this model glycoprotein could be adjusted to desired concentrations using different butyrolactone dosing regime

Synthesis and biological evaluation of some furanones as putative chitinase Inhibitors

Analogs of naturally occurring furanones that were reported to be weak inhibitors of Serratia marcescens chitinases were prepared and tested towards various chitinases. Some of these compounds - but not the natural products - were found to be weak but selective inhibitors; all glycosylated analogs tested were inactive. Activation of the plant enzyme hevamine was observed in one case, which is unusual

Anti-protozoal activity of aporphine and protoberberine alkaloids from Annickia kummeriae (Engl. & Diels) Setten & Maas (Annonaceae)

BACKGROUND: Malaria, trypanosomiasis and leishmaniasis have an overwhelming impact in the poorest countries in the world due to their prevalence, virulence and drug resistance ability. Currently, there is inadequate armory of drugs for the treatment of malaria, trypanosomiasis and leishmaniasis. This underscores the continuing need for the discovery and development of new anti-protozoal drugs. Consequently, there is an urgent need for research aimed at the discovery and development of new effective and safe anti-plasmodial, anti-trypanosomal and anti-leishmanial drugs. METHODS: Bioassay-guided chromatographic fractionation was employed for the isolation and purification of antiprotozoal alkaloids. RESULTS: The methanol extract from the leaves of Annickia kummeriae from Tanzania exhibited a strong anti-plasmodial activity against the multi-drug resistant Plasmodium falciparum K1 strain (IC50 0.12 +/- 0.01 mug/ml, selectivity index (SI) of 250, moderate activity against Trypanosoma brucei rhodesiense STIB 900 strain (IC50 2.50 +/- 0.19 mug/ml, SI 12) and mild activity against Leishmania donovani axenic MHOM-ET-67/82 strain (IC50 9.25 +/- 0.54 mug/ml, SI 3.2). Bioassay-guided chromatographic fractionation led to the isolation of four pure alkaloids, lysicamine (1), trivalvone (2), palmatine (3), jatrorrhizine (4) and two sets of mixtures of jatrorrhizine (4) with columbamine (5) and palmatine (3) with (-)-tetrahydropalmatine (6). The alkaloids showed low cytotoxicity activity (CC50 30 - <90 mug/ml), strong to moderate anti-plasmodial activity (IC50 0.08 +/-