Community survey of ammonia-oxidizing bacteria in full-scale activated sludge processes with different solids retention time.
OBJECTIVE
To study the effects of different solids retention time (SRT) on the nitrification activity and community composition of ammonia-oxidizing bacteria (AOB) in two full-scale activated sludge processes during a 5-month period.


RESULTS
The AOB community composition was analysed using fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE), and the identified populations were enumerated by quantitative FISH. Potential nitrification rates were determined in batch tests and the in situ rates were calculated from mass balances of nitrogen in the plants. Increased SRT reduced the nitrification activity, but neither the number per mixed liquor suspended solids nor community composition of AOB were affected. Two dominant AOB populations related to Nitrosomonas europaea and Nitrosomonas oligotropha were identified by FISH, whereas only the latter could be detected by DGGE.


CONCLUSIONS
The effect of a longer SRT on the activity was probably because of physiological changes in the AOB community rather than a change in community composition.


CONCLUSIONS
Physiological alterations of a stable AOB community are possible and may stabilize activated sludge processes. The commonly used FISH probes designed to target all beta-proteobacterial AOB does not detect certain Nitrosomonas oligotropha populations, leading to an underestimation of AOB if a wider set of probes is not used.
Hallin
S
S
Department of Microbiology, Swedish University of Agricultural Sciences, Box 7025, S-750 07 Uppsala, Sweden. sara.hallin@mikrob.slu.se
Lydmark
P
P
Kokalj
S
S
Hermansson
M
M
Sörensson
F
F
Jarvis
A
A
Lindgren
P-E
PE
D000641:Ammonia / Q000378:metabolism*; D001419:Bacteria / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018533:Biomass; D002449:Cell Aggregation; D048429:Cell Size; D004269:DNA, Bacterial / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D006801:Humans; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D018613:Microscopy, Confocal / Q000379:methods; D009606:Nitrosomonas / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D016133:Polymerase Chain Reaction / Q000379:methods; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA / Q000379:methods; D012722:Sewage / Q000382:microbiology*; D013997:Time Factors
D004269:DNA, Bacterial; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D012722:Sewage; D000641:Ammonia