Effects of soybean oligosaccharides on water quality and microbial community in biofloc systems

The aim of this study was to investigate the effect of soybean oligosaccharides (SBOS) on water quality and microbial communities in biofloc systems. A mixture of starch and glucose (3:7) as a carbon source was used as the control group (Con), and the mixture was replaced with SBOS by 2.5 % (DD1), 5 % (DD2), 7.5 % (DD3), and 10 % (DD4) with C: N of 15 as the experimental group with a duration of 30 days. Results indicated that, compared with control group, the accumulation of nitrite nitrogen (NO -2 -N) was reduced in DD2, DD3, and DD4 by the 7th day ( P < 0.05)；the biofloc volume (FV) peaked in DD4 on the 14th day ( P < 0.05), and there was a significant reduction in nitrate nitrogen (NO -3 -N) accumulation in DD2 by the 28th day ( P < 0.05). In addition, compared with control group, the abundance of Sphingobacterium, Deinococcus was significantly decreased and Bdellovibrio, Niveispirillum was significantly increased in DD2 ( P < 0.05), the metabolic pathways related to transport, signal transduction and nucleotide metabolism was decreased, while metabolism of terpenoids and polyketides, lipid metabolism, and xenobiotics biodegradation and metabolism were increased in DD2 ( P < 0.05). In summary, 5 % SBOS as a carbon source in biofloc systems improved water quality, promoted the population of beneficial bacteria, and reduced the population of harmful bacteria. This study provides both theoretical and practical support for the application of SBOS in biofloc systems, promoting sustainable aquaculture growth and the well-being of aquatic environments. • Soybean oligosaccharides (SBOS) mediated nitrite nitrogen reduction and water quality in biofloc systems. • SBOS altered biofloc composition and optimized microbial communities. • SBOS promoted probiotics and suppressed pathogens. • SBOS stimulated critical metabolic pathways. • 5 % SBOS as the optimal replacement concentration.