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Inactivation of quorum sensing (QS) signal molecules, such as acylhomoserine lactones (AHLs) of pathogenic bacteria, has been proposed as a novel method to combat bacterial diseases in aquaculture. Despite the importance of micro-algae for aquaculture, AHL degradation by bacteria associated with micro-algal cultures has thus far not been investigated. In this study, we isolated Pseudomonas sp. NFMI-T and Bacillus sp. NFMI-C from open cultures of the micro-algae Tetraselmis suecica and Chaetoceros muelleri, respectively. An AHL degradation assay showed that either monocultures or co-cultures of the isolates were able to degrade the AHL N-hexanoyl- l-homoserine lactone. In contrast, only Bacillus sp. NFMI-C was able to inactivate N-hydroxybutanoyl- l-homoserine lactone, the AHL produced by Vibrio campbellii. The isolated bacteria were able to persist for up to 3 weeks in conventionalized micro-algal cultures, indicating that they were able to establish and maintain themselves within open algal cultures. Using gnotobiotic algal cultures, we found that the isolates did not affect growth of the micro-algae from which they were isolated, whereas a mixture of both isolates increased the growth of Tetraselmis and decreased the growth of Chaetoceros. Finally, addition of Bacillus sp. NFMI-C to the rearing water of giant river prawn ( Macrobrachium rosenbergii) larvae significantly improved survival of the larvae when challenged with pathogenic V. campbellii, whereas it had no effect on larval growth. [ABSTRACT FROM AUTHOR]

Vibrios belonging to the H arveyi clade are among the major pathogens of aquatic organisms. Quorum sensing ( QS) is essential for virulence of V . harveyi towards different hosts. However, most virulence factors reported to be controlled by QS to date are negatively regulated by QS, therefore suggesting that their impact on virulence is limited. In this study, we report that QS positively regulates flagellar motility. We found that autoinducer synthase mutants showed significantly lower swimming motility than the wild type, and the swimming motility could be restored by adding synthetic signal molecules. Further, motility of a luxO mutant with inactive QS ( LuxO D47E) was significantly lower than that of the wild type and of a luxO mutant with constitutively maximal QS activity ( LuxO D47A). Furthermore, we found that the expression of flagellar genes (both early, middle and late genes) was significantly lower in the luxO mutant with inactive QS when compared with wild type and the luxO mutant with maximal QS activity. Motility assays and gene expression also revealed the involvement of the quorum-sensing master regulator LuxR in the QS regulation of motility. Finally, the motility inhibitor phenamil significantly decreased the virulence of V . harveyi towards gnotobiotic brine shrimp larvae. [ABSTRACT FROM AUTHOR]

Although aquaculture continues to be the fastest-growing food-producing industry worldwide, the sector faces important challenges with respect to controlling infectious diseases. Indeed, the frequent use of antibiotics, which are traditionally the most important line of defence against bacterial disease, has raised problems related to the development and spread of resistance. As a result, we currently are in a race to develop novel therapeutics that should allow us to continue controlling bacterial disease in the future. In this respect, scientific progress of the past years has allowed us to start understanding the mechanisms by which bacterial pathogens are causing disease. This knowledge in its turn opens up novel possibilities to combat infections by interfering with these mechanisms, a strategy that has been termed antivirulence therapy. In this review, the current knowledge with respect to pathogenicity mechanisms of bacterial aquaculture pathogens is discussed, including adhesion mechanisms, production of extracellular polysaccharides and biofilm formation, production of lytic enzymes (e.g. haemolysins and proteases), mechanisms of iron acquisition, secretion systems and regulatory mechanisms such as quorum sensing and host-pathogen signalling with catecholamine stress hormones. Furthermore, an overview is given of the first steps towards antivirulence therapy for aquaculture, with a focus on quorum sensing disruption as a proof of concept. [ABSTRACT FROM AUTHOR]

Knowledge on the importance of associations between bacteria and microalgae in aquatic ecosystems is rather limited at the moment, mostly due to a lack of studies at the molecular and biochemical level of microorganisms. This paper discusses the current knowledge on microalgae-bacteria interactions and their potential impacts on the productivity, efficiency and sustainability of aquaculture. Current findings suggest that the interactions are complex and specific. The release of stimulatory products by bacteria that enhance the growth of microalgae, and vice versa, indicates the existence of mutualistic relations. Other factors, such as signalling between bacteria and microalgae, may also play an important role. Although these interactions may be of significant importance, to date, only a few findings have been reported on the use of consortia consisting of microalgae and bacteria for practical purposes. Interestingly, these results pointed out that a combination of microalgae and bacteria is often better than using either of them alone. Further research is needed to obtain a thorough understanding of the mechanisms behind the interactions between these microorganisms, including the identification of active compounds. This knowledge will enable the selection of appropriate consortia for different applications in aquaculture, including disease control and high and sustainable production of feed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Quorum sensing inhibitors are promising novel biocontrol agents. [•] Most inhibitors are identified using biosensors, a procedure that is prone to bias. [•] Adequate control experiments are needed to exclude false positives. [•] Toxicity to biosensors should be carefully assessed as well. [ABSTRACT FROM AUTHOR]

Abstract: As the human population continues to grow, food production industries such as aquaculture will need to expand as well. In order to preserve the environment and the natural resources, this expansion will need to take place in a sustainable way. Biofloc technology is a technique of enhancing water quality in aquaculture through balancing carbon and nitrogen in the system. The technology has recently gained attention as a sustainable method to control water quality, with the added value of producing proteinaceous feed in situ. In this review, we will discuss the beneficial effects of the technology and identify some challenges for future research. [Copyright &y& Elsevier]

Poly-β-hydroxybutyrate ( PHB) is a natural polymer that can be depolymerized into water-soluble short-chain fatty acid monomers. These monomers can act as microbial control agents. In this study, the effects of partially replacing the diet of Siberian sturgeon fingerlings with 2% and 5% PHB were investigated. Replacing 2% of the diet with PHB improved weight gain, specific growth rate ( SGR) and survival in the sturgeon fingerlings during the 10-week experimental period. Community-level physiological profiling and PCR-denaturing gradient gel electrophoresis ( PCR- DGGE) were used to analyze the microbial community diversity and community organization in the sturgeon gastrointestinal tract. DGGE analysis revealed that PHB affected the intestinal microbial species richness and diversity. The highest species richness was observed with 2% PHB. DNA sequencing of the dominant bands in 2% and 5% PHB treatments revealed that PHB stimulated bacteria belonging to the genera B acillus and R uminococcaceae. Principal component analysis, Lorenz curves and the Shannon index of Biolog™ Ecoplate data revealed that aerobic metabolic potential of the bacterial community was different in the PHB-treated fishes as compared with the control situation. Overall, our results indicate that PHB act as microbial control agents and replacement of 2% of Siberian sturgeon fingerling diet with PHB has beneficial effects. [ABSTRACT FROM AUTHOR]

Antivirulence therapy, disarming pathogens rather than killing them, is emerging as a novel strategy for disease control. Reporter strains expressing an easily measurable and quantifiable phenotype enable easy screening of virulence inhibitors. In this paper I propose a novel concept to exclude false positives in this type of screening. [ABSTRACT FROM AUTHOR]

Luminescent vibrios, bacteria belonging to the species Vibrio harveyi and closely related species, are important pathogens in aquaculture that can affect almost all types of cultured animals. Due to large-scale use of antibiotics, many luminescent vibrios have acquired (multiple) resistance, which render antibiotic treatments ineffective. One of the alternative strategies that has recently been developed to control infections caused by antibiotic-resistant bacteria is the disruption of quorum sensing, bacterial cell-to-cell communication. The quorum sensing system of V. harveyi has been studied quite intensively in vitro. Recent studies have been directed towards understanding the impact of quorum sensing and quorum sensing disruption on the virulence of luminescent vibrios towards different host organisms in vivo. This mini-review aims at discussing the current knowledge of quorum sensing in luminescent vibrios in vivo. Subsequently, quorum quenching by halogenated furanones is discussed and finally, some directions for further research are presented.The ISME Journal (2008) 2, 19–26; doi:10.1038/ismej.2007.92; published online 25 October 2007 [ABSTRACT FROM AUTHOR]

This study aimed at getting a deeper insight in the molecular mechanism by which the natural furanone ( 5Z)-4-bromo-5-(bromomethylene)-3-butyl-2( 5H)-furanone disrupts quorum sensing in Vibrio harveyi. Bioluminescence experiments with signal molecule receptor double mutants revealed that the furanone blocks all three channels of the V. harveyi quorum sensing system. In further experiments using mutants with mutations in the quorum sensing signal transduction pathway, the compound was found to block quorum sensing-regulated bioluminescence by interacting with a component located downstream of the Hfq protein. Furthermore, reverse transcriptase real-time polymerase chain reaction with specific primers showed that there was no effect of the furanone on luxR Vh mRNA levels in wild-type V. harveyi cells. In contrast, mobility shift assays showed that in the presence of the furanone, significantly lower levels of the LuxRVh response regulator protein were able to bind to its target promoter sequences in wild-type V. harveyi. Finally, tests with purified LuxRVh protein also showed less shifts with furanone-treated LuxRVh, whereas the LuxRVh concentration was found not to be altered by the furanone (as determined by SDS-PAGE). Therefore, our data indicate that the furanone blocks quorum sensing in V. harveyi by rendering the quorum sensing master regulator protein LuxRVh unable to bind to the promoter sequences of quorum sensing-regulated genes. [ABSTRACT FROM AUTHOR]

A poly-β-hydroxybutyrate (PHB)-accumulating enrichment culture was obtained using activated sludge from a polyphosphate-accumulating reactor as inoculum. PHB accumulated by the enrichment culture significantly enhanced the survival of Artemia nauplii, infected with the virulent pathogen Vibrio campbellii LMG 21363. A strain was isolated from the enrichment culture, based on its ability to accumulate PHB, and 16S rRNA gene sequencing of the isolate revealed 99% sequence similarity to Brachymonas denitrificans AS-P1. The isolate, named PHB2, showed good PHB-accumulating activity (up to 32% of the cell dry weight). PHB accumulated by isolate PHB2 was able to protect Artemia completely from the V. campbellii strain. Our data indicate that PHB-accumulating bacteria, such as B. denitrificans PHB2, could be used as an an effective and economically interesting alternative strategy to control infections in aquaculture. [ABSTRACT FROM AUTHOR]

The human-specific HF183Bacteriodes16S rRNA genetic marker can be used to detect human faecal pollution in water environments. However, there is currently no method to quantify the prevalence of this marker in environmental samples. We developed a real-time polymerase chain reaction (PCR) assay using SYBR Green I detection to quantify this marker in faecal and environmental samples. To decrease the amplicon length to a suitable size for real-time PCR detection, a new reverse primer was designed and validated on human and animal faecal samples. The use of the newly developed reverse primer in combination with the human-specific HF183 primer did not decrease the specificity of the real-time PCR assay but a melting curve analysis must always be included. This new assay was more sensitive than conventional PCR and highly reproducible with a coefficient of variation of less than 1% within an assay and 3% between assays. As theBacteroidesspecies that carries this human-specific marker has never been isolated, a bacteria real-time assay was used to determine the detection efficiency. The estimated detection efficiency in freshwater ranged from 78% to 91% of the true value with an average detection efficiency of 83 ± 4% of the true value. Using a simple filtration method, the limit of quantification was 4.7 ± 0.3 × 105 human-specificBacteroidesmarkers per litre of freshwater. The aerobic incubation of the human-specificBacteroidesmarker in freshwater for up to 24 days at 4 and 12°C, and up to 8 days at 28°C, indicated that the marker persisted up to the end of the incubation period for all incubation temperatures. [ABSTRACT FROM AUTHOR]

Indole signalling has been proposed as a potential target for the development of novel virulence inhibitors to control bacterial infections. However, the major structural features of indole analogues that govern antivirulence activity remain unexplored. Therefore, we investigated the impact of 26 indole analogues on indole‐regulated virulence phenotypes in Vibrio campbellii and on the virulence of the bacterium in a gnotobiotic brine shrimp model. The results demonstrated that 10 indole analogues significantly increased the fluorescence of indole reporter strain Vibrio cholerae S9149, 21 of them decreased the swimming motility of V. campbellii, and 13 of them significantly decreased the biofilm formation of V. campbellii. Further, we found that 1‐methylindole, indene, 2,3‐benzofuran, thianaphthene, indole‐3‐acetonitrile, methyl indole‐3‐carboxylate, 3‐methylindole, and indole‐2‐carboxaldehyde exhibited a significant protective effect on brine shrimp larvae against V. campbellii infection, resulting in survival rates of challenged brine shrimp above 80%. The highest survival of shrimp larvae (98%) was obtained with indole‐3‐acetonitrile, even at a relatively low concentration of 20 μM. Importantly, the indole analogues did not affect bacterial growth, both in vitro and in vivo. These results indicate the potential of indole analogues in applications aiming at the protection of shrimp from vibriosis. [ABSTRACT FROM AUTHOR]