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The management of bacterial loading in intensive aquaculture systems is often a key factor in the success of larval cultures, particularly in molluscan hatcheries. Vibrio spp. have often been cited as affecting scallop larvae cultures. Bacteriological studies employing emergent molecular methods may now be of use in molluscan hatcheries to monitor the abundance of total and non-culturable Vibrio spp. In this study, the fluorescence in situ hybridization (FISH) technique with 16S rRNA-targeted oligonucleotide probes was used to quantify the presence of γ-Proteobacteria and Vibrio spp. in the bacterioplankton associated to mass larval cultures in six commercial hatcheries in two geographic regions of northern Chile. Results showed an average of 58% (Region III) and 38% (Region IV) of total cell counts could be detected by hybridization by using probe for domain Eubacteria. Use of the probe for γ-Proteobacteria showed averages between 21% and 28% in these regions, and use of the probe for Vibrio spp. detected percentage between 0.6% and 17%. Direct counts by fluorescence compared with viable plate counts suggested low culturability of the bacterioplankton. Results obtained from the different sampling areas did not reveal a characteristic pattern for each geographic region, nor by culture company. However, some differences were noted between companies with healthy larval cultures and one company which was experiencing mass larval mortalities, emphasizing the relevance of the bacterioplankton in scallop cultures.

Se estudió la relación antagónica entre bacterias bénticas que conforman biopelículas en diferentes substratos marinos. Se examinó un total de 29 cepas aisladas a partir de la macroalga Lessonia nigrescens y los substratos artificiales utilizados en el asentamiento de larvas de ostión (Argopecten purpuratus) y abalón (Haliotis discus hannai). Además, se realizaron ensayos de antibiosis de los 29 aislados contra una bacteria conocida por producir substancias inhibitorias (Vibrio C33). Los resultados confirmaron la ocurrencia de interacciones antagonistas entre los microorganismos aislados a partir de la microbiota adherida a superficies marinas (20,7%). En ninguna de las 329 pruebas de inhibición, se detectó actividad auto-inhibitoria entre los morfotipos seleccionados. L. nigrescens mostró una población microbiana estable con la dominancia de cuatro cepas, siendo una bacteria del grupo β-Proteobacteria (SL5) susceptible a las substancias inhibitorias producidas en el mismo microhábitat. Actividad inhibitoria entre bacterias aisladas de colectores de ostión fue observada solamente con un Vibrio sp. (7,7%). Al evaluar el efecto de la cepa Vibrio C33 contra los 29 aislados, detectamos un efecto antibacteriano frente al 53,8% de las cepas aisladas de los colectores de ostión. No se observaron efectos inhibitorios en los ensayos realizados con las cepas aisladas de la macroalga y colectores de abalón. El análisis filogenético de las cepas susceptibles al Vibrio C33 mostró que todas las bacterias pertenecen al grupo γ-Proteobacteria. Los resultados indican que la producción de substancias inhibitorias es un fenómeno común entre bacterias aisladas de biopelículas, causando ventajas competitivas sobre otras bacterias y jugando importante rol en el control de funciones en microhábitat epifíticos. A study was made of antagonistic relations among benthic bacteria that form biofilms in different marine substrates. A total of 29 strains isolated from the seaweed Lessonia nigrescens and artificial substrates used for scallop (Argopecten purpuratus), and abalone (Haliotis discus hannai) larval settlement were examined for antagonistic activity against other bacteria isolated from the same substrates. Antibiosis assays of all isolates were carried out against a bacterium known to produce inhibitory substances (Vibrio C33). The results confirmed the occurrence of antagonistic interactions among microorganisms isolated from microbiota attached to the marine surfaces (20.7%). In the 329 inhibition tests, auto-inhibition activity among the selected morphotypes was not detected. L. nigrescens showed a stable bacterial population made up of four dominant strains, with one strain, a β-Proteobacteria (SL5) susceptible to the inhibitory substances produced in the same microhabitat. Inhibitory activity among the bacteria isolated from scallop collectors was observed only with one Vibrio sp. (7.7%). Evaluating the effect of strain Vibrio C33 against the 29 isolates, we detected a prominent antibacterial effect against 53.8% of the isolates from scallop settlement substrates. Inhibitory effects were not detected in antibiosis assays done on strains isolated from seaweed and abalone collectors. The phylogenetic analysis of the strains susceptible to C33 showed them all to be members of γ-Proteobacteria. Results indicate that production of inhibitory substances is a common phenomenon among bacteria isolated from bacterial biofilms, giving them a competitive advantage over other bacteria and playing an important controlling function in epiphytic microhabitats.