Three bacterial strains isolated from an abalone postlarval culture system.

Three bacterial strains, GHrC11, GHrC13 and GHrC15, were isolated from an abalone postlarval culture system in a commercial farm at Baja California, México. The strains were phenotypically characterized and sequenced (16S rDNA). Strain GHrC11 was a Gram-positive coccobacillum, while strains GHrC13 and GHrC15 were Gram-negative bacilli. Strain GHrC11 was identified as Exiguobacterium sp. The strains GHrC13 and GHrC15 were identified as Vibrio splendidus. The effects of these strains for the development of early abalone postlarvae (2 days old) were evaluated following a completely randomized design with three replicates using 5-mL-volume Petri dishes as experimental units. The experiment considered two different bacterial concentrations of each strain (10³ and 10⁵ cells ml^-1) and two controls (with and without the benthic diatom Navicula incerta). After 10 days of experimentation, the highest mortality (90 ± 5.8 %) and the lowest growth rate (4.1 ± 0.1 µm day^-1) were recorded for the strain GHrC11. In contrast, the lower mortality (16.7 ± 3.3 %) and the highest growth rate (11.2 ± 0.9 µm day^-1) corresponded to the control fed N. incerta. Our results suggest that pathogenic effects of these bacterial strains were stronger than any potential benefits derived from the ingestion of bacteria by early abalone postlarvae. In conclusion, the most pathogenic strain was GHrC11, and the intensity of pathogenicity could be ordered as Exiguobacterium sp. > V. splendidus (C13) > V. splendidus (C15).