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from
Artemia
showed similarity with five of the nine introduced bacteria, indicating that
those strains may be able to colonize or populate the
Artemia
GI tract and to minimize the
levels of other opportunistic bacteria. The protection of the selected strains was confirmed in
Artemia
cultures challenged with a
V. proteolyticus
shown to cause mortality in monoxenic
Artemia
cultures (Verschuere
et al.
2000b). Pre-emptive colonization by some strains, such as
LVS8 (identified as
Vibrio
sp.), gave total protection against infection (with survival similar
to that of non-infected controls) while other strains such as LVS2, identified as
Bacillus
sp.,
gave only a partial protection and intermediate survival levels (Marques
et al.
2005). The
in
vitro
antagonism tests were negative and extracellular bacterial compounds did not protect
Artemia
. Living cells were required to protect
Artemia
against
V. proteolyticus
, suggesting
that pre-emptive colonization allows the selected strains to compete effectively for nutrients
or adhesion sites with the pathogen and suppress its development (Verschuere
et al.
2000b).
As the probiotic effect can be strongly influenced by the nutritional status of
Artemia
,
the protective effect of two selected bacterial strains,
Bacillus
sp. LVS2 and
A. hydrophyla
LVS3, were tested by Marques
et al.
(2006) on gnotobiotic
Artemia
nauplii fed with
different
Saccharomyces cerevisiae
mutant strains (linked to nutritional factors such as a
lower concentration of mannose or higher concentration of chitin and glucans in the yeast).
Subsequently the
Artemia
were challenged with two bacterial pathogens, the opportunistic
V.
proteolyticus
CW8T2 (Verschuere
et al.
2000b) and the virulent pathogenic
Vibrio campbellii
LMG21363 (Soto-Rodríguez
et al.
2003). This study demonstrated that the quality of the feed
had a stronger protective effect than the added bacteria. Good quality yeasts counteracted the
detrimental effect of both pathogens, and adding probiotic bacteria with them did not give
additional protection. Only when
Artemia
were supplied with lower quality yeast feeds did
probiotics show an effect, counteracting opportunistic
V. proteolyticus
but not the virulent
V. campbellii
. The authors suggest that a higher presence of β-glucans and chitin in the cell
wall of mutant yeasts would provide a possible stimulation of the innate immune system
of
Artemia
. The study of the development of the digestive tract showed an influence of live
A. hydrophyla
LVS3 on cell proliferation of the gut (Gunasekara
et al.
2010) and a slight
increase in the growth of the digestive tract was confirmed by stereology and computer
assisted three-dimensional image reconstruction. The authors hypothesize an increased
cell proliferation in GI epithelia and underlying muscle in
Artemia
which received the live
probiotic bacteria (Gunasekara
et al.
2011).
16.5.4 Probiotics in copepods
It is presumed that bacteria play an important role in the nutrition of copepods in nature and
under cultured conditions. Harpaticoid copepods have been successfully cultured by feeding
only on dried bacteria and on bacterial biofilms, showing a clear preference for certain bacterial
strains (Rieper 1978; Dahms
et al.
2007).
Research on the use of probiotics in copepods is still very scarce, limited to studies on the
beneficial effect of the addition of bacteria, probably due to nutritional factors (Guérin and
Rieper-Kirchner 1992; Guérin
et al.
2001). In a recent study, Drillet
et al.
(2011) tested the
effectiveness of a commercial probiotic preparation (PSI: Sorbial A/S DANISCO, Allonnes,
France) based on heat inactivated
Lactobacillus farciminis
and
Lactobacillus rhamnosus
strains in the calanoid copepod
Acartia tonsa
fed with
Rhodomonas salina
. The addition of
the probiotic to the algal food significantly increased egg production (by 50%), egg hatching
success (by 17%) and female growth (by 10%) in comparison to controls. These effects
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