Molecular Characterization and Gene Expression Profiling ... - CUSAT

Chapter 6
is induced upon bacterial challenge (Supungul et al., 2004; Liu et al., 2005;
Nagoshi et al., 2006).
Also, the expression profile of ALF in response to gram-positive
probiotic Bacillus was found to be similar to that of gram-negative Vibrio
reported by Beale et al. (2008) in the lobster, Homarus americanus. Hence, we
can say that the response of ALF to probiotic bacteria is similar to that of a
pathogen. In terms of ALF expression, it may be explained that probiotic
bacteria mimic a bacterial infection in shrimps that leads to an enhanced
production of potent molecules like ALF, thereby enhancing the immune
resistance of the host organism. de la Vega et al. (2008) have also showed an
enhanced production of ALF in the haemocytes of L. vannamei on V.
penaeicida infection. Recombinant P. monodon ALF showed antimicrobial
activity against fungi, gram-positive and gram-negative bacteria
(Somboonwiwat et al., 2005), and in the crayfish P. lenuisculus ALF has been
implicated in the reduction of WSSV replication. Thus, it is possible to
predict that ALF could function in shrimp as a broad spectrum antimicrobial
peptide. The expression of ALF mRNA detected in unchallenged shrimp
indicated that ALF is constitutively expressed and stored in shrimp
haemocytes. The growing number of relatively conserved ALF genes
identified with apparently conserved functions being characterized across
taxa seems to indicate the likely importance of ALF in shrimp besides the
AMPs in the penaeidin family (Gueguen et al., 2006; Somboonwiwat et al.,
2008).
In the case of crustins also, up-regulation of the gene could be noticed
(though a minor one) on probiotic administration pre-challenge WSSV (Fig.
6.6 – 6.8). This is in agreement with the previous works where crustins have
been found to up-regulate with bacterial invasion in the shrimps
(Jiravanichpaisal et al., 2007; Amparyup et al., 2008). Significant up-
regulation of the crustins has also been reported after the administration of
Molecular Characterization and Gene Expression Profiling of Antimicrobial Peptides in Penaeid Shrimps
354