Metagenomic Studies on Microbial Community Structure of Biofloc System

Abstract

The aims of the present work were investigation of the A. sobria challenge effect on the microbial community structure of water and Nile tilapia gut in both biofloc system and clear water system, investigation of the protective capacity of biofloc system on gills, and skin histopathology of Nile tilapia against A. sobria infection, investigation of the A. sobria challenge effect on the total heterotrophic bacterial count in water and Nile tilapia gut in both biofloc and clear water system, and finally comparing water quality in both systems. Nile tilapia fish were divided into four groups; two groups in the biofloc system (A. sobria challenged group and control group) and two groups in the clearwater system (A. sobria challenged group and control group). Each group consisted of three replicates (11 fish/replicate). These fish were acclimated into twelve tanks for 1 month, during this period water quality parameters were monitored at three sampling dates in both systems. Two fish were randomly selected to confirm the freedom of Aeromonas infection. The fish were infected by an I/P injection of 1.5 × 108 CFU/ml of A. sobria strain. Water and gut samples were aseptically collected for the total heterotrophic bacterial count and microbial community structure analysis before and after infection. Also, gills and skin samples were collected for histopathology before and after infection. Genomic DNA was extracted from water and fish gut samples and subjected to next-generation sequencing using Illumina Novaseq 6000 sequencing platform. Severe histopathological alterations were noticed in CWS, while mild histopathological alterations were noticed in BFT. The skin showed hyperemia grossly without any histopathological alterations