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Rev. biol. mar. oceanogr. 51(1): 101-112




Decreasing of bacterial content in Isochrysis galbana cultures by using some antibiotics

Ceres A. Molina-Cárdenas1, M. del Pilar Sánchez-Saavedra1 and Alexei Fedorovish Licea-Navarro

1Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE),  Carretera Tijuana-Ensenada 3918, Zona Playitas, 22860, Ensenada, Baja California, México

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The southwestern Gulf of California has high-value commercial fisheries; however, there are few studies of the taxonomic diversity of fish in this area. Surveys of taxonomic diversity of the fish assemblage at 8 localities near the shore of Bahía de La Paz were undertaken from March 2002 to April 2003. Seasonal changes in diversity of rocky reef fish were analyzed, including taxonomic distance among fish species, using the alpha, alpha average, beta, and gamma diversity indices, the taxonomic distinctness index (TD D*), and the average taxonomic distinctness index (AvTD D+). Submarine visual censuses were carried out along 48 transects measuring 100 × 5 m (500 m2) at 5 m average depth from 09:00-16:00 h. Two seasons were studied: winter with an average temperature of 22.57°C, and summer with an average temperature of 27.09°C. 24,633 fishes, belonging to 92 species and 67 genera were recorded. According to the alpha average, beta, and gamma diversity indices, August had the highest diversity (19.5, 40.5, and 60 species, respectively), and December had the lowest diversity (20.6, 27.4, and 48 species, respectively). Spatial analysis of TD and AvTD were not significantly different, and analysis by season of these indices was not significant different. Greater anthropogenic impact would cause differences in TD and AvTD found at El Guano compared with other locations.
The axenic microalgae cultures are a difficult task and they are hard to maintain. Microalgae cultures with reduced bacterial load can be an option to axenic microalgae cultures to produce compounds with biotechnological and pharmaceutical potential. Also they can be used for cryopreservation and in biochemical, physiology, ecology and genetic studies. The aim of this study was to develop a protocol to decrease the bacterial load in an Isochrysis galbana culture, through washes by centrifugation and the administration of various antibiotics (ampicillin, neomycin, kanamycin, chloramphenicol, sulphate G418, streptomycin, and carbencillin), at several doses and combinations. The concentrations of heterotrophic bacteria and I. galbana cell densities were monitored daily. Maximum non-lethal concentration and lethal concentration 50% (LC50) were calculated. Individually, antibiotics and washes by centrifugation failed to reduce bacterial load, but their combination removed bacteria from the cultures. Peak survival (84.6 ± 1.4%) and reduction of bacterial load in I. galbana cultures were effected with the combination of 5 washes by centrifugation and administration of a cocktail, comprising ampicillin, kanamycin, neomycin, and streptomycin at 48 h. Values of maximum non-lethal concentration varied from 75 to 106 µg mL-1 and LC50 between 194 and 332 µg mL-1, thus, our protocol is an effective and rapid method of producing I. galbana cultures with reduced bacterial load.

Key words: Bacterial load, Isochrysis galbana, antibiotics, centrifugation