Piscirickettsia salmonis is the bacterium that causes Piscirickettsiosis, a systemic disease of salmonid fish responsible for significant economic losses within the aquaculture industry worldwide. The growth of the bacterium for vaccine formulation has been traditionally accomplished by infecting eukaryotic cell lines, a process that involves high production costs and is time-consuming. Recent research has demonstrated that it is possible to culture pure P. salmonis in a blood containing (cell-free) medium.In the present work we demonstrate the growth of P. salmonis in a liquid medium free from blood and serum components, thus establishing a novel and simplified bacteriological medium. Additionally, the new media reported provides improved growth conditions for P. salmonis, where biomass concentrations of approximately 800 mg cell dry weight L−1 were obtained, about eight times higher than those reported for the blood containing medium. A 2- level full factorial design was employed to evaluate the significance of the main medium components on cell growth and an optimal temperature range of 23–27°C was determined for the microorganism to grow in the novel liquid media.Therefore, these results represent a breakthrough regarding P. salmonis research in order to optimize pure P. salmonis growth in liquid blood and serum free medium.

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Variations of zooplankton abundance and biomass in a tropical oligo-mesotrophic reservoir in Northern Venezuela. Zooplankton abundance in reservoirs is mainly determined by the speed and content of the water, but relatively little is known regarding tropical reservoirs. We studied the seasonal and spatial distribution of zooplankton abundance and biomass along the longitudinal axis of Clavellinos reservoir, northern Venezuela, from October 2006 to September 2007. Zooplankton was collected from the oxygenated layer using a plankton net. A total of 16 taxa were identified: Copepoda, Cladocera, Rotifera, Ostracoda and Diptera. Thermocyclops decipiens (Copepoda, Cyclopoida) dominated the community, while rotifers were the most diverse, with 10 species. Zooplankton abundance varied from 31 to 101ind/L in E1, 36 to 84ind/L in E2, and, from 30 to 250ind/L in E3. Biomass varied from 97.4 to 1406.3µg/l in E1, 108.5 to 397.2µg/l in E2, and from 25.9 to 763.9µg/l in E3. This zooplankton community seems to respond to environmental variations in the reservoir, rather than to variations in resource availability. Rev. Biol. Trop. 58 (2) El embalse es un híbrido de río y lago, en el cual el río embalsado regula y retarda su flujo, se extiende en forma de una capa de agua que alcanza un equilibrio más avanzado, tanto en relación con su entorno físico como con el desarrollo de la vida; la tasa de renovación del agua es más lenta que en un río y más rápida que en un lago (Margalef 1983). La organización vertical del lago y la horizontal del río quedan sustituidas por otra organización intermedia y característica, de la que es un elemento importante la asimetría entre la presa o dique y la cola del embalse (Margalef 1983).

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Piscirickettsia salmonis is a facultative Gram-negative intracellular bacterium that produces piscirickettsiosis, disease that causes a high negative impact in salmonid cultures. The so-far-unidentified nutritional requirements have hindered its axenic culture at laboratory and industrial scales for the formulation of vaccines. The present study describes the development of a defined culture medium for P. salmonis. The culture medium was formulated through rational design involving auxotrophy test and statistical designs of experiments, considering the genome-scale metabolic reconstruction of P. salmonis reported by our group. The whole optimization process allowed for a twofold increase in biomass and a reduction of about 50% of the amino acids added to the culture medium. The final culture medium contains twelve amino acids, where glutamic acid, threonine and arginine were the main carbon and energy sources, supporting 1.65 g/L of biomass using 6.5 g/L of amino acids in the formulation. These results will contribute significantly to the development of new operational strategies to culture this bacterium for the production of vaccines.

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