Effects of biochar on microbial community in bioflocs and gut of Oreochromis niloticus reared in a biofloc system

Abstract

This study investigated the effects of biochar application on the bacterial community structure in bioflocs and intestines of Oreochromis niloticus cultured in a biofloc system and further evaluated its effects on some intestinal enzyme activities. Three carbon treatments, the control G, sole application of glucose; B, sole application of biochar; and GB, glucose plus biochar, were used to set up a biofloc system. Tilapia juveniles were cultured in the biofloc system for 74 days. At the end of the trial, bioflocs and fish were sampled, and microbial community structure was profiled using Illumina Miseq sequencing of the 16S rRNA gene. Also, intestinal enzyme activities including amylase, lipase, and protease were measured using standard ELISA Kits. The results showed that intestinal lipase activity was significantly lower in GB (509.21 ± 35.92 U g−1) compared to B (636.48 ± 52.63 U g−1) but similar between B and G (612.96 ± 23.9 U g−1), respectively. On the phylum level, Chloroflexi was predominant in both bioflocs (36.6%) and the gut (46.68%) of fish in B, whereas Actinobacteria was dominant in the bioflocs (33.95%) and intestinal samples (33.80%) in G. Similarly, Actinobacteria was predominant in GB for both the bioflocs (34.68%) and intestines (40.55%). Also, at the genus level, norank_Caldilineaceae was the dominant genus for group B in both samples. The study showed that bioflocs are abundant and more diverse in bacterial communities compared to the gut of tilapia in biofloc systems and different carbon sources can influence bacterial community structure in both bioflocs and the gut of fish.