The Influence of Geosmin and 2-Methylisoborneol on the Microbial Community Structure in a Recirculating Aquaculture System

The secondary metabolites, geosmin and 2-methylisoborneol (MIB) are known to taint fish with an undesirable, earthy-muddy taste and odor. Also in recirculating aquaculture systems (RAS) the problem of off-flavored fish is increasingly reported. In an earlier study on a zero-discharge recirculating system, we showed that geosmin and MIB are removed by microbial communities residing in the treatment compartments of the system. In the present study, the microbial community structure and its change as a result of geosmin and MIB enrichment, was examined in the nitrifying trickling filter and in the digestion basin of this zero-discharge system. By means of high-throughput 16S rRNA sequencing, significant differences were found between the microbial community structures of the two treatment compartments. Enrichment with geosmin and MIB was found to increase the relative abundance of 8 and 13 operational taxonomic units (OTUs) in the microbial communities of the trickling filter and digestion basin, respectively. In addition to induction of some taxa, other microbial taxa were repressed by geosmin and MIB addition. Among the OTUs with increased relative abundance were those harboring known members of geosmin and MIB degraders. Both in the trickling filter and in the digestion basin, geosmin and MIB enrichment resulted in an increase in relative abundance of two distinct OTUs, affiliated with Sphingobacteriales, suggesting that this latter taxon may play an important role in the geosmin and MIB removal from such systems. Overall, the results presented in this study emphasize the potential for bacterial geosmin and MIB removal in recirculating aquaculture facilities.