Bacteria associated with early life stages of the great scallop, Pecten maximus: impact on larval survivalReport as inadecuate

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* Corresponding author 1 IMR - Institute of Marine Research 2 LEMAR - Laboratoire des Sciences de l-Environnement Marin LEMAR 3 UEB - Université européenne de Bretagne 4 Center for Studies of Environment and Resources, University of Bergen 5 Department of Biology, University of Bergen

Abstract : A bacteriological study was carried out at a scallop Pecten maximus hatchery near Bergen, western Norway following a severe increase in mortality rates during the larval stages of the scallops. No larvae survived to settling, except for those in groups treated prophylactically with chloramphenicol. In order to identify pathogenic strains of bacteria, we performed a challenge test on 10- to 16-day-old larvae using isolated bacterial strains from the hatchery. Infection with six of these strains produced mortalities that were not statistically different from that resulting from infection with the known pathogen Vibrio pectenicida. However, about 5% of the strains tested in the challenge experiment produced higher motility rates than found in the unchallenged control group, indicating a possible probiotic effect. On the basis of 16S rDNA analysis on these strains, the phylogenetic tree indicated two groups of apparent pathogens: 1 one strain, LT13, grouped together with Alteromonas-Pseudoalteromonas; 2 a cluster of strains grouped together with Vibrio splendidus LT06, LT21, LT73, PMV18 and PMV19. Strain LT13 was isolated from cultures of the microalga Chaetoceros calcitrans used for feed, while the other strains were isolated from larval cultures. Transmission electron microscopy showed intracellular bacteria that resembled bacteria in the groups Chlamydiaceae and Rickettsiaceae.

Keywords : Bacteria Challenge experiment Phenotypic characterisation 16S rDNA Scallop Larvae

Author: Lise Torkildsen - Christophe Lambert - Thorolf Magnesen - Are Nylund - Øivind Bergh -



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