Evaluation of inhibitory effect of secondary metabolites of Streptomyces sp. Strain SC 190 on polyphenoloxidase activity to prevent melanosis in Pacific white shrimp (Litopenaeus vannamei)

Abstract

Melanosis is a major problem in the marine crustaceans processing industry particularly on shrimps which can lead to financial loss to producers. The cause of this complication is biochemical reactions of polyphenoloxidase (PPO) enzyme and the formation of the dark pigments on shrimp′s body. The main purpose of the present study was to evaluate the inhibitory effect of secondary metabolites extracted from SC 190 on PPO activity to achieve a potential alternative for chemical inhibitors implemented for control of melanosis on Pacific white shrimp. In this study, the PPO enzyme was extracted from the cephalothorax of shrimp samples and partially purified. The results showed that extracted metabolites from the strain SC 190 isolated from sea cucumber Holothuria scabra represented inhibitory activity on the PPO enzyme with an IC50 value of 60.69 ± 3.76 µg/mL. The bacterial extracted metabolites could scavenge DPPH free radicals with an IC50 value of 45.10±2.14 µg/mL. The result of the toxicity test showed that the extracted metabolites were not toxic to the human umbilical vein endothelial cell lines. Chemical screening approved the existence of phenolic compounds in the extracted bacterial metabolites. Polyphasic identification of SC 190 isolate revealed that it has belonged to Streptomyces genus and its 16S rRNA gene sequence had 99% homology with S. cellulosae. According to the results, the metabolites extracted from Streptomyces sp. Strain SC 190 can be considered as a potential biopreservative in the preservation of Pacific white shrimp.

Keywords

• antioxidant
• metabolite
• melanosis
• pacific white shrimp
• polyphenoloxidase