Effects of dietary peptidoglycan on Litopenaeus vannamei: Growth performance, disease resistance, non-specific immunity and transcriptome analysis of immune response

At present, peptidoglycan (PGN) is commonly used as an immunostimulant in shrimp. However, little has been known about its mechanism. In this study, comparative transcriptome analysis was employed to investigate the impact of dietary PGN on the immune response in Litopenaeus vannamei. A total of 720 healthy juvenile L. vannamei (initial weight 0.31 ± 0.05 g) were randomly evenly allocated to 18 fibreglass buckets as 6 groups, fed with six isonitrogen (41.05%) and isolipid diets (8.16%) containing PGN at the doses of 0 (control), 0.2, 1, 5, 25, and 125 mg/kg, respectively. After 8 weeks feeding trail, the growth performance, immunity, and transcriptome response of L. vannamei were analyzed. The results showed that the growth performance of L. vannamei was not significantly influenced by dietary PGN (P > 0.05). According to the analysis of weight gain rate (WGR), the optimum dietary PGN level was 71.46 mg/kg. Compared with the control group, the survival rate (SR) after Vibrio parahaemolyticus infection of L. vannamei were significantly increased by dietary PGN at 5 mg/kg and the SR after white spot syndrome virus (WSSV) infection was improved by dietary PGN at 25 mg/kg (P < 0.05). The superoxide dismutase (SOD), phenoloxidase (PO), catalase (CAT), lysozyme (LZM), acid phosphatase (ACP), and alkaline phosphatase (AKP) activities could be enhanced remarkably while the maleic dialdehyde (MDA) levels were significantly decreased by dietary PGN compared with the control group (P < 0.05). Transcriptome analysis showed that there were 1350 (902 down, 448 up) and 1697 (1183 down, 514 up) DEGs in the PGN5 and PGN25 when compared with the PGN0 group, respectively. Most DEGs were significantly enriched in immune and metabolism related signalling pathways, such as antigen processing and presentation, autophagy-animal, apoptosis-multiple species, carbohydrate digestion and absorption, and amino sugar and nucleotide sugar metabolism signalling pathway. Besides, the metabolism related signalling pathways occupied top significantly enriched placement. In conclusion, moderate dietary PGN could significantly improve the non-specific immunity of L. vannamei, presumably by modulating its metabolism.