Bacterial diversity, community structure and function associated with biofilm development in a biological aerated filter in a recirculating marine aquaculture system

摘要

A biological aerated filter (100 l), filled with bamboo ball media, was set up for treatment of low ammonia-containing recirculating water in a marine aquaculture system. Chemical analysis showed that it took 70 days to establish a stable efficiency, at which more than 30% of the ammonia was removed. During the biofilm development, bacterial diversity and community structure were determined by construction of 16S rRNA gene libraries. Bacterial diversity and population richness were quite abundant and increased gradually, as revealed by the indexes of Shannon (from 3.34 to 3.94), Simpson (from 0.94 to 0.97) and Margalef (from 7.91 to 14.25). Dominant groups in the whole process showed a regular variation trend: a decrease of uncultured bacteria and Bacteroidetes from 38% to 32% and from 18% to 7%, respectively; and an increase of Alphaproteobacteria from 22% to 41%. In particular, clones closely relating to Denitromonas increased from 1.7% to 6.5% and then to 10% in the libraries A, B and C, respectively; in addition to the only detection of six clones (3%) representing Nitrospira in library C. Furthermore, a few strains capable of heterotrophic ammonia-oxidizing or aerobic denitrifying were isolated from the late phase of the biofilm development. All these results might infer that the biofilm bacterial community gradually shifts from chemical oxygen demand (COD)-removing flora to COD- and nitrogen-removing ones with the biofilm development, and that nitrification, heterotrophic ammonia oxidizing and denitrification all contribute to nitrogen removal of the biofilter.