Agriculture Reference
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Focusing on the contribution of bacteria to nutritional quality, Rico-Mora
etal.
(1995) chal-
lenged
Artemia
cultures with bacterial strains isolated from the diatom
Skeletonema costatum
and observed a positive effect of two strains of
Flavobacterium
and
Aeromonas
on
Artemia
survival. Gorospe
et al.
(1996) also demonstrated that
Pseudomonas
sp. can be a good source
of proteins and amino acids required for growth and survival of
Artemia
in rice-bran culture.
Bacteria can also improve
Artemia
diets based on microalgae. A
Flexibacter
strain isolated
from shrimp ponds added together with the microalgae
Rhodomonas
sp. improved growth and
biomass of
Artemia
, as compared with the culture only with microalgae (Intriago and Jones
1993). This finding suggests the use of bacteria as food as well as a probable probiotic effect
in the digestion of the microalgae.
Orozco-Medina
et al.
(2002) isolated Gram-positive heterotrophic bacteria strains belong-
ing to the genera
Microbacterium
and
Exiguobacterium
from well-performing commercial
cysts. Gnotobiotic (axenic)
Artemia
nauplii fed on autoclaved baker's yeast and challenged
with a mixture of those bacteria showed significantly enhanced growth and development. Both
strains also promoted growth and survival in agnotobiotic (xenic) conditions (Hipólito-Morales
et al.
2009). Light and scanning electron microscopy demonstrated the ingestion of both bac-
teria by
Artemia
nauplii, and fluorescence microscopy allowed the detection of the introduced
bacteria, live and dead, in the gut lumen (Orozco-Medina
et al.
2009a). However, no evidence
was found that those bacteria adhered or colonized the intestinal epithelium and the authors
hypothesized that the probiotic effect can be due to the enzymatic contribution provided by
bacterial proteases to the digestion of baker's yeast (Orozco-Medina
et al.
2009b).
To elucidate whether the effect of bacteria is nutritional or probiotic, Marques
et al.
(2005)
used gnotobiotic
Artemia
challenged with the dead or live bacteria, combined with different
axenic live feeds (yeasts or microalgae) differing in their nutritional values. Dead bacteria
exerted a significant effect on survival when
Artemia
were fed with poor feeds, but a weak
or no effect when good-quality feeds were used. With some strains, such as
Cytophaga
sp.
GR8, isolated from well-performing rotifer cultures (Rombaut
et al.
1999), and
Bacillus
sp.
LVS2, isolated from well-performing
Artemia
cultures (Verschuere
et al.
1999), the addition
of live bacteria improved the performance of
Artemia
cultures compared with the addition of
the same dead bacteria, in all of the feeds supplied. This would indicate a probiotic effect of
those strains, independently of the nutritional effect. This study highlights the importance of
considering the interactions with feeds in the evaluation of the probiotic effect.
The positive effects of selected bacteria in
Artemia
cultures are based not only on their
nutritional or enzymatic contribution but also on their role as bacterial control agent against
pathogenic or opportunistic bacteria, through antagonism or by competition for available
resources (nutrients, space, adhesion sites etc.). Verschuere
et al.
(1999) tested different
bacteria isolated from well-performing
Artemia
cultures, and selected nine (unidentified)
strains based on the positive effect on survival and growth of
Artemia
in monoxenic cultures.
Those strains were used for a pre-emptive colonization of xenic cultures of
Artemia
juveniles,
adding 10
6
bacteria ml
-1
to the culture medium. A positive effect on the survival and/or the
growth rate was observed with all selected strains at 36 h and only the cultures pre-emptively
colonized contained living
Artemia
at the end of the trial (132 h). No significant differences
in total CFU per
Artemia
were observed between treatments but a clear influence of the
pre-emptive colonization was observed in the microbial communities associated with the
Artemia
, as determined with Biolog GN community-level physiological profiles. Although
chemo-taxonomical results were not sufficient to confirm the identity, isolates recovered
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