Probiotic Strains for Shellfish Aquaculture: Protection of Eastern Oyster,Crassostrea virginica, Larvae and Juveniles Againsl Bacterial Challenge

Abstract

Bacterial pathogens, including several Vibrio spp. and Roseovarius crassostreae, cause severe mortality of larval and juvenile eastern oysters. The introduction of beneficial bacterial isolates in oyster hatcheries and nurseries for the biocontrol of bacterial diseases is a good alternative to the use of antibiotics. The goal of this study was to screen and characterize marine bacterial isolates as potential agents to prevent larval and juvenile mortality by the oyster pathogens Vibrio tubiashii and R. crassostreae. Screening of bacterial isolates from Rhode Island marine organisms and environment using agar-based assay methods for detection of antimicrobial activity against oyster pathogens led to the isolation of candidate probionts Phaeobacter sp. S4 and Bacillus pumilus RI06-95. Pretreatment of larval and juvenile oysters for 24 h with 102-106 cfu/mL Phaeobacter sp. S4 or B. pumilus RI06-95 protected larval oysters against mortality resulting from challenge with R. crassostreae and V. tubiashii (relative percent survival (RPS) range, 9%-56%). These probiotics also protected juvenile oysters against challenge with V. tubiashii (RPS, 37%-50%). Probiotic isolates had no negative impact on oyster survival. Protection conferred to larvae against bacterial challenge was short-lived, lasting for only 24 h after removal of the probiotics from the incubation water. These results suggest the potential of marine bacterial isolates Phaeobacter sp. S4 and B. pumilus RI06-95 to serve as biocontrol agents to reduce the impact of bacterial pathogens in the culture of Crassostrea virginica.

Effect of the probiotic strainPhaeobacter gallaeciensisafter bacterial challenge on the complete larval development ofPecten maximus

“…Antibacterial activities associated with this Phaeobacter species had already been reported in previous works aiming to select potential probiotics for bivalve hatcheries (Ruiz-Ponte et al 1999;Prado et al 2009;Kersarcodi-Watson et al 2012;Karim et al 2013). Our results confirm the promising probiotic potential of this strain against pathogens regularly encountered in hatcheries.…”

“…The improvement of survival associated with Phaeobacter sp. treatment had already been demonstrated in hatchery for Ostrea edulis (Prado 2006) and P. maximus (Ruiz-Ponte et al 1999) and for C. gigas using bacterial challenges in smallscale bioassays (Kersarcodi-Watson et al 2012;Karim et al 2013). However, in Ruiz-Ponte, the efficient protection of scallop larvae exerted by P. gallaeciensis was demonstrated only with the bacterial cells broken down using an ultra-sonic treatment while no effects was observed with entire bacteria.…”

“…This difference could be explained by the implementation of a ten days pre-treatment period before the bacterial challenge experiment. Indeed, Karim et al (2013) showed that the probiotic ability of Phaeobacter sp. was significantly enhanced when larvae were exposed for 24 h before bacterial challenge.…”

“…Comparatively to bacterial challenges performed on smallscale bioassays (Kersarcodi-Watson et al 2009Karim et al 2013), our approach simulated conditions more representative of those found in a commercial hatchery (in terms of larval density, hatchery routine and larval development). Thus, our results are complementary to these previous works and validate the usefulness of X34 for P. maximus larval production.…”

“…These experiments were generally followed by in vivo validation of probiotic effects of the selected strains by assessing the improvement in larval survival although this was usually done in the absence of a bacterial challenge. Recently, several studies have developed in vivo validation protocols for probiotics using bacterial challenges in small-scale bioassays (Kesarcodi et al 2009(Kesarcodi et al , 2010(Kesarcodi et al , 2012Karim et al 2013), but these conditions remain very different from those of a commercial production in terms of water volume, larval densities and hatchery routines. Therefore, in this study, we aimed to evaluate the probiotic potential of the "X34" strain of Phaeobacter gallaeciensis on the entire larval development (from veliger stages to metamorphosis) of P. maximus, using a bacterial challenge experiment in conditions closer to those used in hatchery.…”