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A 15-day lab-scale experiment was performed to determine the possible use of bio£ocs as a feed for Macrobrachium rosenbergii postlarvae. The bio£ocs were grown on acetate, glycerol and glucose. A glycerol-fed reactor was initially inoculated with a Bacillus spores mixture. The highest protein content was obtained in the (gly-cerol1Bacillus) bio£ocs, i.e.58 AE 9% dry weight (DW). The glycerol and acetate bio£ocs showed a lower, but similar content (42^43% DW) and glucose bio£ocs contained 28 AE 3% DW. Higher total n-6 fatty acid contents were observed in the glycerol and (glycerol1 Bacillus) bio£ocs. The vitamin C content was variable, up to 54 mg ascorbic acid g À 1 DW in the glycerol bio-£ocs. Bio£ocs were fed to M. rosenbergii postlarvae as the sole feed. High survival levels were obtained in the (glycerol1Bacillus) and glucose groups, i.e. 75 AE 7% and 70 AE 0% respectively. This was signi¢cantly higher than the starvation control (0% survival after 15 days). This indicated that the prawns were able to feed on the bio£ocs. These results are in accordance with the bio£oc's nutritional parameters and suggest that the choice of the carbon source used for growing bio£ocs is of prime importance.

Autoinducer 2 (AI-2) quorum sensing was shown before to regulate the virulence of Vibrio harveyi towards the brine shrimp Artemia franciscana. In this study, several different pathogenic V. harveyi, Vibrio campbellii, and Vibrio parahaemolyticus isolates were shown to produce AI-2. Furthermore, disruption of AI-2 quorum sensing by a natural and a synthetic brominated furanone protected gnotobiotic Artemia from the pathogenic isolates in in vivo challenge tests.Bacteria belonging to the species Vibrio harveyi and the closely related Vibrio campbellii and Vibrio parahaemolyticus are important pathogens in the intensive rearing of mollusks, finfish, and shrimp (1,7,10,11,14,19,25). The traditional control of bacterial disease in aquaculture relies on the use of antibiotics (3,21). However, the frequent use of these compounds, in many cases even when pathogens are not evident, has led to the development and spread of resistance (3,10,13,23,24). Therefore, there is an urgent need for alternative control techniques. Disruption of quorum sensing, bacterial cell-to-cell communication by means of small signal molecules, has been suggested as a new anti-infective strategy for aquaculture (4).The quorum sensing system of V. harveyi has been shown to consist of three channels (8). Recently, we found that the autoinducer 2 (AI-2)-mediated channel of the system regulates the virulence of the bacterium towards the brine shrimp Artemia franciscana in vivo (5). Interestingly, halogenated furanones were found to interfere with AI-2 quorum sensing in Escherichia coli (16,17) and were shown before to block quorum sensing-regulated extracellular toxin production in V. harveyi, resulting in a reduced toxicity of cell-free culture fluids to Penaeus shrimp (12). Therefore, in this study, we aimed at investigating whether these halogenated furanones could reduce the virulence of V. harveyi and closely related bacteria in our model system with gnotobiotic Artemia franciscana.Detection of AI-2 production by the pathogenic isolates. In a first experiment, we aimed at detecting AI-2 production by the different pathogenic V. harveyi, V. campbellii, and V. parahaemolyticus isolates. The isolates tested are described in Table 1.Cell-free culture fluids of the isolates were prepared, and autoinducers were detected by a bioluminescent reporter assay as described before (22). The autoinducer receptor double mutant JMH597 (sensor HAI-1 Ϫ , sensor AI-2 ϩ , sensor CAI-1 Ϫ ) (8) was used as a reporter strain. The culture fluids of all isolates significantly induced bioluminescence in the reporter strain (data not shown), indicating that they all produced AI-2. The detection of AI-2 in cell-free culture supernatants of V. harveyi and V. parahaemolyticus confirms the report of Bassler et al. (2), who used the HAI-1 receptor mutant BB170 as a reporter strain. To the best of our knowledge, this is the first report mentioning AI-2 production by V. campbellii.Disruption of AI-2 quorum sensing in V. harveyi by the natural furanone. A second in vitro experim...