Temporal bacterial community succession during the start-up process of biofilters in a cold-freshwater recirculating aquaculture system

Start-up of biofilters plays crucial roles in the successful operation of recirculating aquaculture system, and the nature is bacterial community succession. We explored the pattern of bacterial temporal succession during the start-up process of biofilters in a commercial cold-freshwater recirculating aquaculture system (RAS). The whole succession process was divided into three distinct phases: incubation, growth and stability. Phylogenetic diversity and evenness of the bacterial community increased during the start-up process, whereas richness reached its peak at the growth phase. Seven biomarkers were identified, namely Cytophagales, Gemmatimonadales, Sphingomonadales, Sphingobacteriales, Rhizobiales, Clostridiales and Nitrospirales. The relative abundances of these functional bacteria increased, while those with a competitive growth advantage declined. The network interactions were dramatically altered from fairly simple to most complex, and then decreased in complexity during start-up. Positive relationships decreased, while competition increased. The shift in predicted function exhibited a trend from simple to diverse, and converged to idiosyncratic configuration.