title: Quantifying community dynamics of nitrifiers in functionally stable reactors.
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 for 84 days. It was investigated whether the functional stability of the nitrification process corresponded with a static ammonia-oxidizing bacterial (AOB) community. The SBR provided complete nitrification during nearly the whole experimental run, whereas the MBR showed a buildup of 0 to 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 [Delta(t)((week))] parameter and (ii) the Pareto-Lorenz curve distribution pattern. During the whole sampling period, it was observed that neither of the reactor types maintained a static microbial community and that the SBR evolved more gradually than the MBR, particularly with respect to 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 this was true 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.
authors.affiliation: Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
authors.forename: Lieven
authors.initials: L
authors.lastname: Wittebolle
authors.forename: Han
authors.initials: H
authors.lastname: Vervaeren
authors.forename: Willy
authors.initials: W
authors.lastname: Verstraete
authors.forename: Nico
authors.initials: N
authors.lastname: Boon
mesh_terms: D001419:Bacteria / Q000145:classification* / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D019149:Bioreactors / Q000382:microbiology*; D015169:Colony Count, Microbial / Q000379:methods; D016172:DNA Fingerprinting / Q000379:methods; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D009573:Nitrites / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D017422:Sequence Analysis, DNA; D012722:Sewage / Q000382:microbiology; D013997:Time Factors; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods
chemical_list: D004269:DNA, Bacterial; D009573:Nitrites; D000644:Quaternary Ammonium Compounds; D012722:Sewage