A new ALF from Litopenaeus vannamei and its SNPs related to WSSV resistance

Anti-lipopolysaccharide factors （ALFs） are basic components of the crustacean immune system that defend against a range of pathogens. The cDNA sequence of a new ALF, designated nLvALF2, with an open reading flame encoding 132 amino acids was cloned. Its deduced amino acid sequence contained the conserved functional domain of ALFs, the LPS binding domain （LBD）. its genotnic sequence consisted of three exons and four introns, nLvALF2 was mainly expressed in the Oka organ and gills of shrimps. The transcriptional level of nLw4LF2 increased significantly after white spot syndrome virus （WSSV） infection, suggesting its important roles in protecting shrimps from WSSV. Single nucleotide polymorphisms （SNPs） were found in the genomic sequence of nLvALF2, of which 38 were analyzed for associations with the susceptibility/resistance of shrimps to WSSV. The loci g.2422 A〉G, g.2466 T〉C, and g.2529 G〉A were significantly associated with the resistance to WSSV （P〈0.05）. These SNP loci could be developed as markers for selection of WSSV-resistant varieties ofLitopenaeus vannamei.

Effects of different enzymatic hydrolysis methods on the bioactivity of peptidoglycan in Litopenaeus vannamei

The effects of different hydrolysis methods on peptidoglycan （PG） were assessed in terms of their impact on the innate immunity and disease resistance of Pacific white shrimp, Litopenaeus vannamei. PG derived from Bifidobacteriurn thermophilum was prepared in the laboratory and processed with lysozyme and protease under varying conditions to produce several different PG preparations. A standard shrimp feed was mixed with 0.05% PG preparations to produce a number of experimental diets for shrimp. The composition, concentration, and molecular weight ranges of the soluble PG were analyzed. Serum phenoloxidase and acid phosphatase activity in the shrimp were determined on Days 6-31 of the experiment. The protective activity of the PG preparations was evaluated by exposing shrimp to white spot syndrome virus （WSSV）. Data on the composition of the PG preparations indicated that preparations hydrolyzed with lysozyme for 72 h had more low-molecular-weight PG than those treated for 24 h, and hydrolysis by protease enhanced efficiency of hydrolysis compared to lysozyme. SDS-PAGE showed changes in the molecular weight of the soluble PG produced by the different hydrolysis methods. Measurements of serum phenoloxidase and acid phosphatase activity levels in the shrimp indicated that the PG preparations processed with enzymes were superior to the preparation which had not undergone hydrolysis in enhancing the activity of the two serum enzymes. In addition, the preparation containing more low-molecular-weight PG enhanced the resistance of the shrimp to WSSV, whereas no increased resistance was observed for preparations containing less low-molecular-weight PG. These findings suggest that the immunity-enhancing activity of PG is related to its molecular weight and that increasing the quantity of low-molecular-weight PG can fortify the effect of immunity enhancement.