MOLECULAR MICROBIAL DIVERSITY IN A NITRIFYING REACTOR SYSTEM WITHOUT SLUDGE RETENTION

Recently, the single reactor system for high activity ammonia removal over nitrite (SHARON) process was developed for the removal of ammonia from wastewater with high ammonia concentrations. In contrast to norm al systems, this nitrifying reactor system is operated at relatively h igh temperatures (35 degrees C) without sludge retention. Classical me thods to describe the microbial community present in the reactor faile d and, therefore, the microorganisms responsible for ammonia removal i n this single reactor system were investigated using several complemen tary molecular biological techniques. The results obtained via these m olecular methods were in good agreement with each other and demonstrat ed successful monitoring of microbial diversity. Denaturing gradient g el electrophoresis of 16S rRNA PCR products proved to be an effective technique to estimate rapidly the presence of at least four different types of bacteria in the SHARON reactor. In addition, analysis of a 16 S rRNA gene library revealed that there was one dominant (69%) clone w hich was highly similar (98.8%) to Nitrosomonas eutropha. Of the other clones, 14% could be assigned to new members of the CytophagalFlexiba cter group. These data were qualitatively and quantitatively confirmed by two independent microscopic methods. The presence of about 70% amm onia oxidizing bacteria was demonstrated using a fluorescent oligonucl eotide probe (NEU) targeted against the 16S rRNA of the Nitrosomonas c luster. Electron microscopic pictures showed the typical morphology of ammonia oxidizers in the majority of the cells from the SHARON reacto r. (C) 1998 Federation of European Microbiological Societies. Publishe d by Elsevier Science B.V. All rights reserved.