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Appl. Environ. Microbiol. doi:10.1128/AEM.01006-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Quantifying community dynamics of nitrifiers in functionally stable reactors

Laboratory of Microbial Ecology & Technology (LabMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium

^* To whom correspondence should be addressed. Email: Nico.Boon{at}UGent.be.

	Abstract

A sequential batch reactor (SBR) and a membrane bioreactor (MBR) were inoculated with the same sludge from a municipal wastewater treatment plant, supplemented with ammonium and operated in parallel during 84 days. It was investigated whether functional stability of the nitrification process corresponded with a static ammonia-oxidizing bacterial community. The SBR provided complete nitrification during nearly the whole experimental run, whereas the MBR showed a build-up of 0-2 mg nitrite-N liter^-1 from day 45 until day 84. Based on the denaturing gradient gel electrophoresis profiles, two novel approaches were introduced to characterize and quantify the community dynamics and interspecies abundance ratios: (i) the rate of change (_t(week)) parameter and (ii) the Pareto-Lorenz curve distribution pattern. It was observed that during the whole sampling period, neither of the reactor types maintained a static microbial community and that the SBR evolved more gradually than the MBR, particularly with respect to ammonia-oxidizing bacteria (AOB; i.e. average weekly community changes of 12.6 ± 5.2% for the SBR and 24.6 ± 14.3% for the MBR). Based on the Pareto-Lorenz curves, it was observed that only a small group of AOB species played a numerically dominant role in the nitritation of both reactors, and especially for the MBR. The remaining less dominant species were speculated to constitute a reserve of AOB, which can proliferate to replace the dominant species. The value of these parameters in terms of tools to assist the operation of activated sludge systems is discussed.