Biosynthesis of a trypanocide by Chromobacterium violaceum

Radio-isotope studies indicated not only that l-tryptophan can serve as carbon source for synthesis of the trypanocide, violacein by Chromobacterium violaceum (BB-78 strain) but also that isatin and indole 3-acetic acid are both important metabolic intermediates. Using 3-indolyl [2-¹⁴C] and [1-¹⁴C] acetic acid, it was found that the carboxylic carbon was not eliminated and that indole-3-acetic acid was incorporated intact into the pigment structure. N-Ethyl(5-hydroxy-indol-3-yl)-2-indolylethylamide is also an important metabolic intermediate in the violacein biosynthesis. This is the first report of a metabolic scheme for violacein synthesis which includes an intermediate other than l-tryptophan.     

Conversion from Tryptophan Precursor into Violacein Pigments by a Cell-free System from Chromobacterium violaceum

A cell-free system for converting tryptophan precursor into violacein pigments is reported. Crucial factors were the requirements of the reduced nicotinamides as a cofactor and Zn²⁺ as a metal ion. Optimal pHs were in the range of 8.5–9.5. The effectiveness of NADH was thirty times lower than that of NADPH at a low concentration of 2mm. The oxygenation mechanism(s) is discussed by using oxygenase inhibitors such as amethopterin, metyrapone, ancymidol, and prohexadione. Metal-chelating agents strongly inhibited the biosynthesis, suggesting that metallo-enzymes are involved in the biosynthesis.     

Production, extraction and purificationof violacein: an antibiotic pigment producedby Chromobacterium violaceum

A procedure for the production, extraction, and purification of violacein was developed using Chromobacterium violaceum (CCT 3496) cultivated on cotton, in modified 1 litre Roux bottles. A surface tray bioreactor was built to perform these experiments. Violacein was extracted with commercial ethanol, and purified by filtration, Soxhlet extraction, crystallization and high performance liquid chromatography. The violacein was analysed and identified by proton and carbon-13 NMR spectroscopies, thermogravimetric analysis, mass spectrometry, UV-VIS spectroscopy and infrared spectroscopy. It was concluded that the product was highly purified violacein.     

Inhibition of quorum sensing in Chromobacterium violaceum by pigments extracted from Auricularia auricular

Aims: This study aimed to search for a novel quorum‐sensing inhibitor from some fungi and analyse its inhibitory activity. Methods and Results: Chromobacterium violaceum CV026, a double mini‐Tn5 mutant, was used as an indicator to monitor quorum‐sensing inhibition. Auricularia auricular pigments from fruiting bodies were extracted using hydrochloric acid as an infusion, dissolved in alkaline dimethylsulfoxide (DMSO), sterilized by filtration through a 0·22‐μm membrane filter and added to C. violaceum CV026 cultures. Inhibitory activity was measured by quantifying violacein production using a microplate reader. The results have revealed that the alkaline DMSO‐soluble pigments significantly reduced violacein production in a concentration‐dependent manner, a quorum‐sensing‐regulated behaviour in C. violaceum. Conclusions: Auricularia auricular pigments can inhibit bacterial quorum sensing. Significance and Impact of the Study: The results suggest the bioactive constituents from edible and medicinal fungi could interfere with bacterial quorum‐sensing system, regulate its associate functions and prevent bacterial pathogenesis. Further studies were in process in our laboratory to isolate specific compounds from A. auricular pigments, evaluate them as quorum‐sensing inhibitors and analyse the exact mechanism of action.     

Inhibition of bacterial quorum sensing by vanilla extract

AIMS: The purpose of this study was to search for a novel quorum sensing inhibitor and analyse its inhibitory activity. METHODS AND RESULTS: Quorum sensing inhibition was monitored using the Tn-5 mutant, Chromobacterium violaceum CV026. Vanilla beans (Vanilla planifolia Andrews) were extracted using 75% (v/v) aqueous methanol and added to C. violaceum CV026 cultures. Inhibitory activity was measured by quantifying violacein production using a spectrophotometer. The results have revealed that vanilla extract significantly reduced violacein production in a concentration-dependent manner, indicating inhibition of quorum sensing. CONCLUSIONS: Vanilla, a widely used spice and flavour, can inhibit bacterial quorum sensing. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that the intake of vanilla-containing food materials might promote human health by inhibiting quorum sensing and preventing bacterial pathogenesis. Further studies are required to isolate specific substances from vanilla extract acting as quorum sensing inhibitors.     

Quorum Sensing Signaling Molecules Involved in the Production of Violacein by Pseudoalteromonas

The production of violacein by Pseudoalteromonas sp. 520P1 has many features of quorum sensing. Signaling molecules were extracted from bacterial culture and subsequently identified as N-(3-oxooctanoyl)-homoserine lactone and N-tetradecanoyl-homoserine lactone. The former but not the latter induced the production of violacein in strain 520P1. We conclude that N-(3-oxooctanoyl)-homoserine lactone is a signaling molecule involved in the production of violacein.     

Violacein and biofilm production in Janthinobacterium lividum

AIMS: To analyse the environmental stimuli modulating violacein and biofilm production in Janthinobacterium lividum. METHODS AND RESULTS: Violacein and biofilm production by J. lividum DSM1522(T) was assayed in different growth conditions. Our data suggest that violacein and biofilm production is controlled by the carbon source, being inhibited by glucose and enhanced by glycerol. J. lividum produced violacein also in the presence of different sub-inhibitory concentrations of ampicillin. As opposite, the production of N-acylhomoserine lactone(s), quorum sensing regulators was shown to be positively regulated by glucose. Moreover, violacein-producing cultures of J. lividum showed higher CFU counts than violacein-nonproducing ones. CONCLUSIONS: Taken together, our results suggest that violacein and biofilm production could be regulated by a common metabolic pathway and that violacein as well as biofilm could represent a response to environmental stresses and a key factor in the survival mechanisms of J. lividum. SIGNIFICANCE AND IMPACT OF THE STUDY: Although several recent studies disclosed a number of interesting biological properties of violacein, few data are reported on the physiologic function of violacein in J. lividum. This paper adds new information on the complex mechanisms allowing and regulating bacterial life in hostile environments.