IDENTIFICATION AND ACTIVITIES IN-SITU OF NITROSOSPIRA AND NITROSPIRA SPP. AS DOMINANT POPULATIONS IN A NITRIFYING FLUIDIZED-BED REACTOR

Bacterial aggregates from a chemolithoautotrophic, nitrifying fluidize d bed reactor were investigated with microsensors and rRNA-based molec ular techniques. The microprofiles of O-2, NH4+, NO2-, and NO3- demons trated the occurrence of complete nitrification in the outer 125 mu m of the aggregates. The ammonia oxidizers were identified as members of the Nitrosospira group hy fluorescence in situ hybridization (FISH), No ammonia- or nitrite-oxidizing bacteria of the genus Nitrosomonas or Nitrobacter, respectively, could be detected by FISH, To identify the nitrite oxidizers, a 16S ribosomal DNA clone library was constructed and screened by denaturing gradient gel electrophoresis and selected c lones were sequenced. The organisms represented by these sequences for med two phylogenetically distinct clusters affiliated with the nitrite oxidizer Nitrospira moscoviensis. 16S rRNA-targeted oligonucleotide p robes were designed for in situ detection of these organisms. FISH ana lysis showed that the dominant populations of Nitrospira spp, and Nitr osospira spp. formed separate, dense clusters which were in contact wi th each other and occurred throughout the aggregate. A second, smaller , morphologically and genetically different population of Nitrospira s pp, was restricted to the outer nitrifying zones.