The bacteria from large-sized bioflocs are more associated with the shrimp gut microbiota in culture system

Biofloc technology (BFT) has been widely studied and applied in aquaculture, but the bacterial community compositions (BCCs) of bioflocs with different sizes and their associations with the shrimp gut microbiota remain unclear. In this study, bacterial communities of shrimp gut and the bioflocs with three different size-fractions (BS, < 20 mu m; BM, 20-100 mu m; BL, > 100 mu m) were investigated by MiSeq sequencing technique. Significantly different bacterial communities were observed between the large ( > 20 mu m) and small ( < 20 mu m)-sized bioflocs. The linear discriminant analysis (LDA) showed that certain particle-bound bacteria, such as Rhodobacteraceae and Flavobacteriaceae were mainly enriched in large-sized bioflocs ( > 20 mu m). A majority of these taxa were strongly correlated with shrimp health or water environmental parameters. However, some candidate pathogens (i.e., Vibrionaceae, Mycoplasmataceae and Pseudoalteromonadaceae) were over-represented in small-sized bioflocs ( < 20 mu m), and most of them exhibited negative correlation with shrimp growth parameters. Moreover, multiple analyses (Bray-Curtis dissimilarity analysis, Mantel test, SourceTracker analysis) revealed that the shrimp gut microbiota were more relevant to the bacterial communities of large-sized bioflocs, indicating that the shrimp gut microbiota may partly derived from large particle of bioflocs, and these bacteria driven by large particles may play an important role in promoting shrimp growth.