Research into the hemocyte immune response of Fenneropenaeus merguiensis under decapod iridescent virus 1 (DIV1) challenge using transcriptome analysis.

The banana shrimp (Fenneropenaeus merguiensis) is a common cultural species worldwide. With the development of the shrimp farming industry, increasing number of diseases have emerged and cause huge impacts. Decapod iridescent virus 1 (DIV1) is a new virus of the family Iridoviridae isolated in China that causes very high mortality in shrimp. In this study, DIV1 and PBS were injected into two groups of shrimp, and hemocytes were collected for comparative transcriptomic analysis. We confirmed that F. merguiensis was the new host of DIV1 by nested PCR. A total of 100,759 unigenes were assembled from the control group and the DIV1 infected group, with an average length of 733.06 bp and N50 of 1136 bp. Significant hits were found in 21,465 unigenes compared to known sequences in major databases including COG (33.30%), GO (42.17%), KEGG (46.76%), KOG (61.37%), Pfam (66.90%), Swissprot (54.21%) and Nr (93.86%). A total of 1003 differentially expressed genes (DEGs) were identified, including 929 up-regulated genes and 74 down-regulated genes. Several known immune-related genes, including caspase, C-type lectin, Wnt5 and integrin, were among the differentially expressed transcripts. A total of 14,459 simple sequence repeats, including 8128 monomers, 3276 dimers, 1693 trimers, 150 quadmers, 4 pentamers and 16 hexamers, were found in the transcriptomic dataset. Our study is the first comprehensive investigation of the transcriptomic response to DIV1 infection in F. merguiensis. Collectively, these results not only provide valuable information for characterizing the immune mechanisms of the shrimp responses to DIV1 infection, they open new ways for the study of the molecular mechanisms of DIV1 infection in F. merguiensis.

Dietary supplementation with polypeptides improved growth performance, antibacterial immune and intestinal microbiota structure of Litopenaeus vannamei.

Antibacterial peptides (AMPs) are expected to replace some or all of the antibiotics and become a new feed additive. However, the high production cost and unclear mechanism limited the application of AMPs. In this research, the effects of a commercial polypeptide (Polypeptide S100) whose main components are AMPs on the growth, antibacterial immune and intestinal microbial of Litopenaeus vannamei were study. L. vannamei (initial weight of 0.16 ±â€¯0.03 g) were fed for 123 days with basal diet added Polypeptide S100 at two levels each (0.5% and 1%) as experimental groups, and a basal diet as control. Dietary inclusion of Polypeptide S100 at 1% level significantly increased the weight gain (WG) and specific growth rate (SGR) of L. vannamei. The survival rates of L. vannamei in 0.5% and 1% Polypeptide S100 groups were significantly higher than the control when infected by Vibrio harveyi but not Vibrio parahaemolyticus. The activities of total superoxide dismutase (T-SOD) and lysozyme (LZM) in the two experimental groups were all significantly higher than the control. Differently, the activities of amylase (AMS) and lipase (LPS) were significantly higher in 0.5% Polypeptide S100 group but lower in 1.0% Polypeptide S100 group. Illumina MiSeq high-throughput sequencing showed that the dominant phyla in the intestine of L. vannamei were Proteobacteria, followed by Actinobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Fusobacteria and Tenericutes, and the abundance of predominant phyla Cyanobacteria were upregulated significantly in the experimental groups. At the family level, significant increase was observed in Pseudomonadaceae and Xanthomonadaceae but decrease in Vibrionaceae in the 1.0% Polypeptide S100 group. The abundance of predominant genus Photobacterium were obviously downregulated in the two experimental groups. Unlikely, the abundance of Pseudomonas and Stenotrophomonas were distinctly increased in the 1.0% Polypeptide S100 group but not significantly different from the control in 0.5% Polypeptide S100 group. All these results suggested that Polypeptide S100 could improve the growth performance, antibacterial immune and intestinal microbiota structure of L. vannamei.