Effect of different carbon sources on microbial community structure and composition of ex-situ biofloc formation

Biofloc technology (BFT) is an important application in aquaculture which based on conventional wastewater treatment systems. The most important part of BFT is biofloc (BF), which was made up of microbial community mostly. In this study, we explored the microbial communities in different bioflocs produced from three carbon sources (glucose, starch and glycerol), which were marked as BF (glu)、BF (sta) and BF (gly) respectively. These bioflocs were incubated for 25 days without animals. High-throughput sequencing was used to better understand microbial community composition and structure in BF. The results showed that Shannon diversity index was 5.83 ± 0.15 in BF (gly), 5.64 ± 0.07 in BF (glu) and 4.66 ± 0.35 in BF (sta). These meaned that there were more diverse microbial communities attached to and existed inside the BF(gly). A total of 15 different phyla and 30 families were observed. Phyla Proteobacteria and Bacteroidetes represented >70% of the total microbial for all bioflocs. Notably, Cyanobacteria phylum was most abundant in BF (sta), accounted for 29%, almost ten and forty times than BF (glu) and BF (gly). In addition, aquaculture pathogenic bacteria of Vibrio was absent in BF (sta). The reason why Vibrio was suppressed in BF (sta) remains unknown. Overall the study indicated that carbon source can significantly affect the microbial community composition、structure of biofloc and number of pathogens, suggesting that the choice of the carbon sources used in BFT is very important.