Microflora in biofilters from recirculating aquaculture systems.
Aims: Geosmin is associated with off-flavour problems in recirculating aquaculture systems (RAS) and represents an economic problem for the aquaculture industry. The present study aims at investigating the bacterial microflora and the identity of the known geosmin producers in European RAS. In addition, the environmental and farming factors favouring its accumulation were investigated.Methods and Results: The presence of potential geosmin producers was investigated in the microbial communities of 26 different RAS from four European countries. Furthermore, three novel groups of geosmin-producing bacteria were quantified by qPCR and compared to various water quality parameters to identify potential correlations with geosmin and geosmin-producing bacteria. Results and Conclusions: The microbiome differed significantly between systems. However, phosphate levels, calcium levels and redox potential correlated to the geosmin concentration in the water and the presence of the Actinomycetales geosmin-producers, but not with the presence of the other groups of geosmin-producing bacteria. Oxygen levels and conductivity were found to negatively correlate with the geosmin concentration. A large proportion of the detected geosmin producers represented novel taxonomic groups not previously linked with this activity.Signi?cance and Impact of the Study: These results improve our understanding of the diversity of microbiota in RAS and the environmental factors favouring the populations of geosmin-producing bacteria and the geosmin production.