Metagenomic Analysis Of Epidemic-related Pathogens In Cultured Penaeus Vannamei And Scophthalmus Maximus

Penaeus vannamei and Scophthalmus maximus(turbot)are introduced to China from abroad for mariculture economic animals.At present,the production of both in China has an absolute advantage in the global scale.In the present study,the disease samples were Penaeus vannamei with "glass post-larvae disease" from a farm in Tangshan,Hebei Province and three batches of turbot from a farm in Sanshan,Laizhou,Shandong Province with different periods of disease.Both samples were investigated for pathogens,and novel viruses and pathogenic bacteria were found to be potentially pathogenic by metagenome sequencing and other means.A novel Marnavirus,named Baishivirus(Gen Bank: ON550424),was identified in Penaeus vannamei by metagenome sequencing.Compared with known viruses,the nucleic acid sequence homology region of the genome only accounted for 8% of the whole genome,with 64.96% similarity.And its pathogenicity was further determined by animal experiments.On this basis,an RT-q PCR assay was established to achieve rapid detection of Baishivirus nucleic acid using the ORF2 gene fragment of Baishivirus as the target.Novel Alloherpesvirus and Scophthalmid herpesvirus were found in the first and second batches of diseased turbot,respectively,with conserved genes encoding amino acid sequences with 57% and 47% similarity to known viruses,respectively.A visual LAMP assay targeting the capsid maturation protease gene fragment of Sm HV-1 allowed the detection of the pathogen within 30 min with a detection limit of 23 copies/μL.In addition,metagenomic analysis of bacteria in the first two batches of samples showed that Vibrio was the main causative agent in the first round of the outbreak;in the second round,Aeromonas salmonicida as a potential causative agent together with Sm HV-1 virus caused turbot mortality.For the third round of samples,the causative agent Edwardsiella piscicida was identified by traditional isolation and culture methods.This paper provides important clues and evidence to support the control of outbreaks in farmed Penaeus vannamei and turbot.Meanwhile,the established rapid detection method for two viruses is beneficial for disease prevention and reduction of economic losses.