Biology Reference
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Roseobacter sp. (strain 27-4) was inoculated to rotifers and then delivered
to the larvae challenged with a pathogenic Vibrio anguillarum (strain 90-
11-287 serotype O1), mortalities were reduced signifi cantly (between 10
and 30%) after 10 d (Planas et al., 2006). The strain was detected in the
gastrointestinal lumen of the larvae but apparently could not colonize it
as it disappeared or diminished after inoculation stopped (Planas et al.,
2006). Roseobacter could not inhibit the growth of the pathogens in co-
culture assays (Hjelm et al . , 2004), nor was it able to reduce V. anguillarum
counts in the larvae or better colonize the larvae, so it is speculated that
Roseobacter is able to perform the antagonistic effect only at specifi c sites
in the larvae (Planas et al . , 2006). This strain of Roseobacter was isolated
from a healthy turbot larvae rearing system in Spain and showed a strong
inhibitory action against V. anguillarum, V. splendidus , and Pseudoalteromonas
sp. by the well diffusion agar assay (Hjelm et al . , 2004). Another strain of
Roseobacter , BS107 isolated from scallop ( Pecten maximus ) larval cultures
in Brest, France, was inoculated directly and its cell extracts to P. maximus
larvae and challenged with L. anguillarum A496 (Ruiz-Ponte et al . , 1999).
Signifi cant reduction in the mortalities of larvae was recorded only with
the cell extracts of the potential probiont. Since the live BS107 strain could
not protect the larvae against action of the pathogen, it still cannot be
considered a true probiont. The cell extract therefore acted as antibacterial
substances that controlled the pathogen.
Other bacteria have been tested (Decamp, 2008; Gatesoupe, 1989;
Gatesoupe, 1991), but in all of them, the experimental designs did not
include (or it was not clear) a pathogen and thus it can be questioned if they
acted as probionts, feed additives or adjuvant, or immunostimulants.
Kesarcodi-Watson et al. (2009) showed that 40 of 69 unidentifi ed bacterial
colonies isolated from healthy aquaculture facilities were able to protect
Greenshell TM mussel larvae ( Perna canaliculus ) when challenged with
two pathogenic vibrios. Larval survival with these probionts improved
between 21.3 and 87.4% . It was shown that a pre-exposure time of 20 h to
the probiont prior to the pathogen inoculation positively infl uenced the
outcome of the assay. The results of this study suggest that a competitive
exclusion mechanism plays a signifi cant role in the protective action of
these probionts if they are allowed to colonize the larvae before a pathogen
enters the system.
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