Rapid pathogen discovery in diseased turbot (Scophthalmus maximus) using 16S rRNA high throughput sequencing

Pathogenic bacterium discovery using 16S rRNA high throughput sequencing has become more commonplace. It offers advantages of being high-throughput screening, cost-effective (less than $15 per sample), and rapid (less than one week). Fish pathogens causing aquatic bacterial diseases outbreak represent a major threat to aquaculture industry. A haemorrhagic disease in turbot (Scophthalmus maximus) outbreaks with unknown etiology in Haiyang, China. Initial analyses suggested it was a bacterial disease based on gross pathology of diseased fish containing ascitic fluid from the distended abdomen, a swollen intestine, an inflamed and red mouth. To fully understand the accurate etiology, distribution of pathogenic bacterium and comprehensive information on the diseased turbots is required. Tested tissues (ascites, heart, eye, mouth, intestine, spleen, and liver) with typical symptoms of diseased turbots were collected and 16 s rRNA sequencing was performed using the Illumina Mi-Seq platform. Sequencing results revealed generally low microbial diversity (< 50 %) in different infected tissues, but the microbiota did exhibit a little higher diversity in the intestine than in the other tissues. A key finding was that Edwardsiella was the most abundant genus detected in all the fish tissues. It was indicated that Edwardsiella spp. was the main causative pathogen in the diseased turbot. The evidence also suggested that Edwardsiella spp. as a severely pathogenic bacteria may cause disruption of the healthy balance in the host. Our study was a new attempt to investigate unknown pathogens in clinical marine fish specimens through the high-throughput nextgeneration sequencing technology.