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14 Immobilization of Phaeobacter 27-4 in biofilters • Biofilters In aquaculture, the concept of probiotics has been extended to bacteria which can exert their beneficial effect on the host by modification of the microbial community associated with fish or seawater, improving the quality of fish environment (Verschuere et al., 2000). Strategies of seawater treatment with addition of beneficial bacteria would be also included. Recirculating Aquaculture Systems (RAS) are the newest form of fish farming production system, more adapted to fulfil environmental constraints (e.g. generating low emissions or making coastal location unnecessary). RAS are typically an indoor system that allows for farmers to control environmental conditions all-year round, being considered better than conventional flow-through systems from an environmental (Neori et al., 2007) and bio-security (Pruder, 2004) point of view. In the last years, RAS systems have been investigated for cultivation of different fish species larvae (Faulk and Holt, 2005; Martins et al., 2009). Seawater quality of aquaculture facilities equipped with RAS is maintained by a diversity of microbial community associated with biofilters (Gross et al., 2003; Michaud et al., 2006; Sugita et al., 2005). Recirculation of seawater tends to stabilize the microbial community and make it more persistent to perturbations (Attramadal et al., 2005). Biofilters colonized with non-opportunistic bacteria have been previously used for production of matured seawater, which increased survival of Atlantic halibut yolk sac larvae (Skjermo et al., 1997) and improved the growth of turbot larvae (Salvesen et al., 1999) by improving microbial seawater quality. Some probiotic bacteria, with antagonistic activity towards fish pathogens have also the capability to produce biofilms. Alpha proteobacteria belonging to the Roseobacter clade have demonstrated to produce tropodithietic acid (Brinkhoff et al., 2004; Bruhn et al., 2005; Porsby et al., 2008), which inhibits different bacterial groups (Brinkhoff et al., 2004) including some fish pathogens (Bruhn et al., 2005; Porsby et al., 2008; Ruíz-Ponte et al., 1999). Production of this antibiotic is related to biofilm formation (Bruhn et al., 2007). Therefore, biofilters could be inoculated and colonized by biofilm-forming probiotic bacteria, improving the permanence of the probiotics in the rearing system and protecting the larvae from opportunistic and potential pathogenic bacterial strains.
New strategies for the control of bacterial infections in marine fish larval rearing 15 1.2.1.3. Inhibiting or inactivating detrimental bacteria in the system • Bacteriophages Bacteriophages are virus particles that infect bacteria. In nature, it has been suggested that bacteriophages are one of the main causes of mortalities in bacterial populations. The principle in the use of bacteriophages in aquaculture is their application for the control of bacterial diseases (Imbeault et al., 2006; Park et al., 2000). The advantage of such strategy is the avoidance of antibiotics use and other therapeutic agents. The drawback of this approach is that the ability of bacteriophages to reduce numbers of bacteria is characterized of high specificity. Production of virus particles specific for the pathogenic bacterial strains in question is therefore required at each time. In addition, resistance to bacteriophages is quickly developed after a relatively short period of time due to short generation time of bacteria. The advantages of bacteriophage therapy against pathogenic bacteria are the following: i) The high specificity results in protection of intestinal microbiota. ii) The ability of propagation. Once susceptible bacteria are present in the fish, then few additions of bacteriophage may be sufficient for protection against pathogens (Nakai and Park, 2002). There is a limited application, however, as mortalities in larviculture are seldom attributed to specific pathogens. In a specific hatchery however, it can occur that problems with mortalities in larvae rearing tanks are related to specific pathogens, so in such cases a tailor-made solution with bacteriophage therapy could be an alternative solution. Bacteriophages have shown encouraging results in the case of protection of shrimp larvae against Vibrio harveyi (Karunasagar et al., 2007). • Interference with Quorum Sensing Quorum Sensing (QS) is a mechanism by which bacteria coordinate the expression of certain genes in response to their population density by producing, releasing and detecting small signal molecules, inducing a physiological response which
Page 1: INSTITUTO DE ACUICULTURA CONSEJO SU
Page 5: The work presented in this Ph.D. Th
Page 8 and 9: viii López Cabo do grupo de tecono
Page 11 and 12: INDEX 1. INTRODUCTION: NEW STRATEGI
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Page 18 and 19: xviii Abstract The third step consi
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Chapter I. Real-time PCR detection
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Chapter II. Colonization and reside
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80 Immobilization of Phaeobacter 27
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6 CHAPTER III
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Final Discussion, Conclusions & Fut
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8. RESUMO EN GALEGO (ABSTRACT IN GA
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Anexo competencia por nutrientes li
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Anexo Phaeobacter 27-4 é inocua pa
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Anexo para os patóxenos da familia
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Anexo probióticos. As colonias de
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Anexo 8.5. Capítulo III: Aplicaci
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Anexo Austin, B., Brunt, J.W., 2009
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Anexo Huys, L., Dhert, P., Robles,
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Anexo Skjermo, J., Vadstein, O., 19
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