Impact of commercial probiotics (Bacillus subtilis) addition during biofloc start-up: water quality, nitrogen conversion, nutrition and microbial community

Abstract

Although probiotics are used widely in aquaculture, the role of probiotics in biofloc construction is still unclear. This study evaluated the impact of commercial Bacillus subtilis addition during biofloc start-up on water quality, nitrogen conversion, nutritional composition, and microbial community. Four treatments were tested: control (Ctr, without B. subtilis and glucose addition), glucose addition (Glu), B. subtilis addition (Bac), and B. subtilis, glucose co-addition (G + B). Results showed no significant difference in the construction time among the four groups, whereas a significant difference was detected in total ammonia nitrogen removal rates between the Ctr and Glu groups (p < 0.05). Glucose-added groups (Glu and G + B) showed significantly higher crude protein, essential amino acids, and total amino acids than non-glucose groups (Ctr and Bac) (p < 0.05). Polyunsaturated fatty acids in Bac (19.53 ± 0.88 %) and G + B groups (22.78 ± 0.84 %) were significantly higher than Ctr group (p < 0.05). Bac group displayed the highest microbial abundance, and the relative abundance of Bacillus genus was significantly higher in Glu and G + B groups than Ctr and Bac groups (p < 0.05). These results indicate that the addition of commercial B. subtilis with glucose enhances biofloc nutrition and has a synergistic effect in optimizing biofloc composition and functionality, suggesting that it should be recommended in the production. This study provides theoretical support for the productional culturing of biofloc and contributes to the understanding of the role of probiotics in biofloc.