Cytryn, E., Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot, Israel, Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, Volcani Center, Bet-Dagan, Israel
Minz, D., Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, Volcani Center, Bet-Dagan, Israel
Gieseke, A., Max Planck Institute for Marine Microbiology, Bremen, Germany
Van Rijn, J., Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot, Israel, Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, PO Box 12, Rehovot, 76100, Israel

In this study, microscopic and molecular microbial analyses were integrated to characterize rapidly developing white filamentous tufts in a fluidized bed reactor used for nitrate removal from a marine recirculating fish culture system. Formation and rapid elongation of the tufts (often exceeding 50 mm day -1) was strongly correlated to transient elevated sulfide concentrations (>50 μM) in the reactor. The dominant bacterial constituents of these tufts were filamentous gram-negative bacteria with densely packed intracellular sulfur granules. Using 16S rRNA gene analysis and fluorescence in situ hybridization it was found that these filamentous bacteria represented a novel Thiothrix phylotype closely related (97% sequence identity) to a previously identified Thiothrix strain endogenous to the marine crustacean Urothoe poseidonis. In addition to filamentous morphotypes, rosette-shaped morphotypes of Thiothrix were also detectable within the tufts. © 2006 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved.