Abstract:
Identification of Single Nucleotide Polymorphism (SNP) related to streptococcosis resistance in Nile tilapia (Oreochromis niloticus) was initially carried out by investigation degree of disease tolerance of fish and consequently identification of SNP was performed. Intramuscular injection of Streptococcus agalactiae was done in fish of 8.56 4.37 g fish when LD50 was obtained at 2.43 x 104 CFU/ml within 14 days post-injection. The bacteria at the concentration of 2.43 x 104 CFU/ml was then injected into the fish of an average weight of 9.74 8.16 g obtained from 7 different stations each of 100 fish. After 14 days post-injection the result showed that fish from different sources exhibited significantly different in degrees of survival rate (P0.05). The survival rates were observed at 82.80 0.38 %, 77.40 0.42 %, 76.00 0.43 %, 68.40 0.48 %, 61.00 0.49 %, 31.00 0.47 % and 16.80 0.38 % in fish from stations TF1, TF5, TF2, TF6, TF3, TF4 and TF7, respectively. The immune genes in both death and survived fish were then analyzed using PCR-Single Strand Conformation Polymorphism (PCR-SSCP) technique. A total of 77 fish from group of highest mortality rate (TF1) and lowest mortality rate (TF7) were used for PCR reaction using specific primers of the immune genes. The PCR products of 11 immune genes were observed including BPI / LBP, TCR, MHC class II, NOD1, transferrin, IgM heavy chain, CD8, TCR, IL8, granzyme and hepcidine with base pair sizes of 121, 148, 207, 207, 209, 300, 395, 407, 408, 461 and 473, respectively. Polymorphisms were then examined by nondenaturing polyacrylamide gel electrophoresis for SSCP analysis. It was found that amplicons from 10 gene-specific primers including BPI/LBP, TCR, MHC class II, NOD1, transferrin, IgM heavy chain, CD8, TCR, IL8 and hepcidine showed no difference in polymorphism. However, polymorphism was detected in granzyme in which DNA sequencing was 99% similar to Oreochromis niloticus granzyme. In this gene, SNP was found in 6 positions including 87, 225, 264, 276, 425 and 433, which substitute patterns of G>A, A>G, A>G, A>C, A>T and A>G, respectively. SNP at nucleotide position
of 425 and 433 of fish in the group highest survival rate (TF1) found to significantly relate to disease resistant (P<0.05). While significant relation was only found in nucleotide position of 433 in fish of lowest survival rate (TF7). These SNPs are potentially developed as DNA marker for streptococcosis resistance in Nile tilapia.
WALAILAK UNIVERSITY. CENTER FOR LIBRARY RESOURCES AND EDUCATIONAL MEDIA