Co-occurrence patterns in biofloc microbial communities revealed by network analysis and their impact on the host

The complex aggregation of bacteria flocs (bioflocs) plays a vital role in the inorganic nitrogen transformation process within biofloc systems. However, few reports have focused on the bacterial co-occurrence of flocs sup-plemented with different carbohydrate sources. In this study, a correlation-based microecological network analysis method was applied to reveal the bacterial interactions of flocs under three different aquaculture sys-tems: a clear water system (CON group), a biofloc system using glucose (GLU) as a carbon source, and a biofloc system using starch (STA) as a carbon source. The results showed that (i) the GLU group exhibited higher ni-trogen removal efficiency and a higher DOC/total inorganic nitrogen ratio (68.80 & PLUSMN; 9.18% and 19.19 & PLUSMN; 6.78, respectively) than the STA group (55.59 & PLUSMN; 16.26% and 15.30 & PLUSMN; 11.08, respectively). The bacterial co-occurrence patterns in the three systems were not random, with each carbohydrate corresponding to a unique bacterial community niche. (ii) Firmicutes was the core phylum in the biofloc technology (BFT) system, while Bacillus, Carnobacterium, and Staphylococcus were the core genera that ensured the stability of nitrogen removal in the system based on network analysis results. (iii) In the GLU group, the abundance of Firmicutes was increased and corresponded to a higher Firmicutes/Bacteroidetes (F/B) ratio in the fish gut, which promoted host in situ growth performance. Application of the ecological concepts in this study could lead to the identification of core/satellite genera in bioflocs and promote scientific hypotheses toward more in-depth metabolic and func-tional research on biofloc systems.