Temporal dynamics of bacterial populations in recirculating aquaculture systems for sea urchin production / Dinámica temporal de poblaciones bacterianas en sistemas de recirculación para la producción acuícolas de erizo de mar

Abstract Introduction: Sea urchin aquaculture is a rising industry, and in consequence, there is a need to establish optimal culture parameters to ensure the health of the cultured animals. Objective: To evaluate the bacterial counts in the seawater of sea urchin (Arbacia dufresnii) aquaculture recirculating systems (RAS). Methods: The bacteriological water quality of two RAS containing sea urchins was determined. For approximately two months, weekly water samples were taken. The bacteriological quality was determined by counting total aerobic heterotrophic populations, lactic acid bacteria, enterobacterias and genus Vibrio. Physicochemical parameters were also measured. Results: There was no presence of disease or mortality. Enterobacteria and lactic acid bacteria were not detected from both RAS systems. The number of animals had an important effect on the observed difference in the count of total bacteria and Vibrio spp. In RAS 1 the maximum counts of total bacteria and Vibrio spp. were 2.8 x 105 ± 1.7 x 105 and 1.45 x 105 ± 3.6 x 104 UFC ml-1, respectively. In RAS 2 total bacteria and Vibrio spp. exhibited repetitive behavior over time influenced in part by water exchange and mainly by feeding. The results indicate that periodic water changes ensure a limited growth of bacterial strains as Vibrio and other bacteria. Conclusions: Our results suggests that the bacterial count levels recorded in this study can be used as a threshold or safety limit for Arbacia dufresnii aquaculture.

Resumen Introducción: La acuicultura de erizos de mar es una industria en auge, y en consecuencia, existe la necesidad de establecer los parámetros de cultivo óptimos para garantizar la salud de los animales en cultivo. Objetivo: Evaluar los recuentos bacterianos en el agua de cultivo de los sistemas de recirculación acuícola (RAS) de erizo de mar Arbacia dufresnii. Métodos: Se determinó la calidad bacteriológica del agua de cultivo de dos RAS que contenían erizos de mar. Durante aproximadamente dos meses, se tomaron muestras de agua semanalmente. La calidad bacteriológica se determinó realizando recuento de las poblaciones heterótrofas aerobias totales, bacterias ácido lácticas, enterobacterias y bacterias del género Vibrio. También se midieron parámetros fisicoquímicos. Resultados: No se observaron patologías ni mortalidad. No se detectaron enterobacterias ni bacterias del ácido láctico en ninguno de los sistemas RAS. El número de animales cultivados tuvo un efecto importante en la diferencia observada en el recuento de bacterias totales y Vibrio spp. En el RAS 1 los recuentos máximos de bacterias totales y Vibrio spp. fueron 2.8 x 105 ± 1.7 x 105 y 1.45 x 105 ± 3.6 x 104 UFC ml-1, respectivamente. En RAS 2 los recuentos de bacterias totales y Vibrio spp. exhibieron un comportamiento repetitivo en el tiempo influenciado en parte por el recambio de agua y principalmente por la alimentación. Los resultados indican que los cambios periódicos de agua aseguran un crecimiento limitado de cepas bacterianas como Vibrio y otras bacterias. Conclusiones: Nuestros resultados sugieren que los niveles de recuento bacteriano registrados en este estudio pueden usarse como umbral o límite de seguridad para la acuicultura de Arbacia dufresnii.

Potential aquaculture probiont Lactococcus lactis TW34 produces nisin Z and inhibits the fish pathogen Lactococcus garvieae.

Bacteriocin-producing Lactococcus lactis TW34 was isolated from marine fish. TW34 bacteriocin inhibited the growth of the fish pathogen Lactococcus garvieae at 5 AU/ml (minimum inhibitory concentration), whereas the minimum bactericidal concentration was 10 AU/ml. Addition of TW34 bacteriocin to L. garvieae cultures resulted in a decrease of six orders of magnitude of viable cells counts demonstrating a bactericidal mode of action. The direct detection of the bacteriocin activity by Tricine-SDS-PAGE showed an active peptide with a molecular mass ca. 4.5 kDa. The analysis by MALDI-TOF-MS detected a strong signal at m/z 2,351.2 that corresponded to the nisin leader peptide mass without the initiating methionine, whose sequence STKDFNLDLVSVSKKDSGASPR was confirmed by MS/MS. Sequence analysis of nisin structural gene confirmed that L. lactis TW34 was a nisin Z producer. This nisin Z-producing strain with probiotic properties might be considered as an alternative in the prevention of lactococcosis, a global disease in aquaculture systems.