Agriculture Reference
In-Depth Information
microorganisms share the same aquatic environment, the concept of probiotics includes also
microorganisms which exert a beneficial effect not only by colonizing the host but also by being
present in the water (see
Chapters7and8
). The different modes of action of probiotics include:
production of inhibitory compounds (e.g. antibiotics, bacteriocins, organic acids, oxygen per-
oxide), competition for limiting nutrients (e.g. siderophores for iron), enzymatic contribution
to digestibility of feed, competence in adhesion to mucus, stimulation of the host immune sys-
tem or improvement of water quality (Verschuere
et al.
2000a; Gram and Ringø 2005; Vine
et al.
2006; Kesarcodi-Watson
et al.
2008, Dimitroglou
et al.
2011). In some cases, the benefi-
cial effect requires the combination of several mechanisms. Replacement of the opportunistic
bacteria in live feeds by a preventive colonization with probiotic bacteria, with persistence in
the water or in live feed, has therefore been proposed as a strategy to improve live feed cultures
and to provide protection to the larvae.
16.5.1 Probiotics in microalgae
Antibacterial activity of some microalgae species, such as
Tetraselmis suecica
(Austin
et al.
1992) or
Skeletonema costatum
(Naviner
et al.
1999), against fish pathogens has been demon-
strated. For example,
S. costatum
extracts inhibited the growth of
V. anguillarum
,
V. mytili
,
and pathogenic
Vibrio
spp. S322 and VRP (Naviner
et al.
1999). Microalgae-associated bac-
teria can also have antagonistic effect. This effect has been reported in
Tetraselmis chuii
and
Chlorella minutissima
towards the fish pathogens
Photobacterium damselae
subsp.
piscida
and
V. anguillarum
(Makridis
et al.
2006). Furthermore, bacteria associated with microalgae
cultures can have a probiotic effect due to nutritional properties (e.g. essential amino acids,
PUFAs) or enzymatic activities (proteolytic or lypolytic), which improve larval feeding and
feed utilization (Riquelme and Avendaño-Herrera 2003).
Suminto and Hirayama (1997) demonstrated a positive effect of a
Flavobacterium
strain
on the growth of axenic cultures of the diatom
Chaetoceros gracilis
but not on the growth of
the phytoflagellates
Isochrysis galbana
and
Pavlova lutheri
. However, the addition of the bac-
teria extended the maintenance of high cell densities in the stationary growth phases for both
microalgae. These results suggest specific algae-bacteria interactions, and therefore benefi-
cial strains could be selectively isolated from microalgae in non-axenic cultures. This approach
was recently used by Rivas
et al.
(2010), who isolated a biofilm-forming
Rhizobium
sp. from
Botryococcus braunii
cultures. The bacteria, re-inoculated into microalgae cultures, acted as
a probiotic and significantly enhanced microalgae growth, indicating a possible use of the
bacteria as inoculum for microalgae mass cultures.
16.5.2 Probiotics in rotifers
The first approaches to the use of probiotics to improve the growth of rotifers were con-
ducted using commercial lactic acid bacteria (LAB) additives or selected LAB (
Lactobacillus
plantarum
and
Lactobacillus helveticus
) (Gatesoupe
et al.
1989). Although the application
of these bacteria did not improve rotifer production rates, in some cases they improved the
rotifer nutritional value, reduced the bacterial load or inhibited specifically the growth of
fish pathogens such as
Aeromonas salmonicida
(Gatesoupe 1991). Similarly, Douillet (2000a)
reported enhancement in the growth of rotifers by adding selected commercial bacterial prod-
ucts (including
Bacillus
and
Pseudomonas
strains), though repeated trials were not consistent.
Planas
et al.
(2004) obtained rotifer growth rates 8-13 times higher than control cultures,
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