Phylogenetic and functional diversity of the bacterial community associated to blooms of toxic phytobenthos

Trabajo final presentado por Encarna Borrull Francesch para el Máster en Ciencias del Mar: Oceanografía y Gestión del Medio Marino de la Universitat de Barcelona (UB) y la Universitat Politècnica de Catalunya (UPC), realizado bajo la dirección de la Dra. Maria Montserrat Sala del Institut de Ciències del Mar (ICM-CSIC).-- 43 pages, 12 figures, 4 tablesBlooms of the benthic dinoflagellate Ostreopsis have been associated with respiratory disorders in humans and mass mortalities in fish. A bloom of Ostreopsis sp. appears regularly in summer in Sant Andreu de Llavaneres beach. The bloom has been associated with respiratory symptoms, rhinitis and skin irritation in bath users. Although several studies have shown the contribution of bacteria to harmful dinoflagellate blooms, the composition and activity of the bacterial community associated to blooms of Ostreopsis in situ has not been assessed. For this reason, a two-year sampling was carried out in Sant Andreu de Llavaneres. The main aims of this study were 1) to characterize the bacterial community to assess their possible contribution to the toxicity of the bloom and 2) to evaluate the effects of the bloom, and the mucilage associated, for the activity of the bacteria. The results of this study have brought three main conclusions: 1. Epiphytic bacteria on macrophytes are significantly more active than bacteria in the water. During periods of blooms, epiphytic bacteria are significantly more active than during periods when Ostreopsis was not present. 2. The bacterial community in the macrophyte shows higher activities of most of the extracellular enzyme activities during the blooms and a significantly higher utilization of carboxylic acids and carbohydrates, suggesting their major contribution in the composition of the mucilage. 3. The epiphytic bacterial community associated to the bloom appears to have a higher diversity than the community in the water or in non-bloom periods. 4. The DNA sequences obtained from the DGGE gels show the presence of several bacterial strains (mainly Vibrio) which contain tetradotoxin and may very likely contribute to the toxicity of the bloom