The quorum-sensing disrupter (5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone (furanone) of the alga Delisea pulchra was found to inhibit the swarming motility of Escherichia coli completely at 13 microg cm-2 (also at 20 microg ml-1) but did not inhibit its growth rate at 13-52 microg cm-2 or from 20 to 100 microg ml-1. Swimming was not inhibited by the furanone at 20-40 microg ml-1. In addition, confocal scanning laser microscopy revealed that this furanone at 60 microg ml-1 inhibited the biofilm formation of E. coli, as it decreased its thickness by 55%, reduced the number of water channels and decreased the percentage of live cells by 87%. This suggests that natural furanone may be used as a new method to control bacterial biofilms that does not involve toxicity. Furanone at 10 microg ml-1 also inhibited by 3300-fold the quorum sensing of Vibrio harveyi via autoinducer 1 (AI-1) and inhibited by 5500-fold that of V. harveyi via of autoinducer 2 (AI-2) as well as inhibited by 26-600-fold the quorum sensing of E. coli via AI-2; hence, this furanone is a non-specific intercellular signal antagonist.

Aims: (5Z)-4-Bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone (furanone) of the marine alga Delisea pulchra was synthesized, and its inhibition of swarming motility and biofilm formation of Bacillus subtilis was investigated. Methods and Results: Furanone was found to inhibit both the growth of B. subtilis and its swarming motility in a concentration-dependent way. In addition, as shown by confocal scanning laser microscopy, furanone inhibited the biofilm formation of B. subtilis. At 40 lg ml )1 , furanone decreased the biofilm thickness by 25%, decreased the number of water channels, and reduced the percentage of live cells by 63%.Conclusions, Significance and Impact of the Study: Natural furanone has potential for controlling the multicellular behaviour of Gram-positive bacteria.

Cucumber (Cucumis sativa) leaves infiltrated with Pseudomonas syringae pv. syringae cells produced a mobile signal for systemic acquired resistance between 3 and 6 h after inoculation. The production of a mobile signal by inoculated leaves was followed by a transient increase in phenylalanine ammonia-lyase (PAL) activity in the petioles of inoculated leaves and in stems above inoculated leaves; with peaks in activity at 9 and 12 h, respectively, after inoculation. In contrast, PAL activity in inoculated leaves continued to rise slowly for at least 18 h. No increases in PAL activity were detected in healthy leaves of inoculated plants. Two benzoic acid derivatives, salicylic acid (SA) and 4-hydroxybenzoic acid (4HBA), began to accumulate in phloem fluids at about the time PAL activity began to increase, reaching maximum concentrations 15 h after inoculation. The accumulation of SA and 4HBA in phloem fluids was unaffected by the removal of all leaves 6 h after inoculation, and seedlings excised from roots prior to inoculation still accumulated high levels of SA and 4HBA. These results suggest that SA and 4HBA are synthesized de novo in stems and petioles in response to a mobile signal from the inoculated leaf.

No abstract

No abstract

No abstract

The isolation and structure determination of two bacterial signal molecules which elicit active plant defense responses are reported. The production of these molecules by Gram-negative bacteria requires the action of avirulence gene D (avrD), cloned from Pseudomonas syringae pv. tomato. The structures of syringolide 1 (la) and syringolide 2 (lb) are determined by a combination of NMR experiments, biosynthetic arguments, molecular modeling, and X-ray crystallography. A proposed biosynthetic scheme based on the condensation of D-xylulose with a d-ketoalkanoic acid is presented. Further cyclization of the biosynthetic intermediates leads to C-glycosides with a novel tricyclic ring system. These are the first nonproteinaceous specific elicitors of a plant hypersensitive response.

actinomycin D,26 and oxytocin.27 Only in the case of c2/cZo-(Pro-Gly)s in methylene chloride do these rules fail to agree with previous conclusions, and this failure (26) D. J. Patel, et ah, unpublished results. (27) A.