title: Quantification of Nitrosomonas oligotropha and Nitrospira spp. using competitive polymerase chain reaction in bench-scale wastewater treatment reactors operating at different solids retention times.
abstract: The effect of solids retention time (SRT) on ammonia-and nitrite-oxidizing bacteria was measured by Nitrosomonas oligotropha-like ammonia monooxygenase A and Nitrospira 16S rDNA competitive polymerase chain reaction assays in a complete-mix, bench-scale, activated-sludge system. During steady-state operation, nitrification was complete in the 20- and 10-day SRT reactors, nearly complete in the 5-day SRT reactor, and incomplete in the 2-day SRT reactor (76% ammonia oxidation and 85% nitrite oxidation). Total microbes, measured by dot-blot hybridizations, ranged from 3 x 10(11) to 3 x 10(12) cells/L, and increased with increasing SRTs. The concentration of the ammonia-oxidizer N. oligotropha dropped 100-fold from the 20-day SRT (5 x 10(9) cells/L) to the 2-day SRT (< or = 4 x 10(7) cells/L). Thus, N. oligotropha became a much smaller fraction of the total biomass in the poorly performing 2-day SRT reactor. The concentration of Nitrospira cells also decreased (10-fold) as the SRT was reduced from 20 days to 2 days. However, the number of Nitrospira cells was always greater than the number of N. oligotropha cells measured in each reactor (10- to 60-fold). While Nitrospira comprised 1 to 2% of the biomass, N. oligotropha represented only 0.04 to 0.27% of the total population. This low percentage suggests that N. oligotropha was not a dominant ammonia oxidizer in the bench-scale systems.
authors.affiliation: Center for Environmental Biotechnology, University of Tennessee, Knoxville 37996, USA.
authors.forename: H M
authors.initials: HM
authors.lastname: Dionisi
authors.forename: A C
authors.initials: AC
authors.lastname: Layton
authors.forename: K G
authors.initials: KG
authors.lastname: Robinson
authors.forename: J R
authors.initials: JR
authors.lastname: Brown
authors.forename: I R
authors.initials: IR
authors.lastname: Gregory
authors.forename: J J
authors.initials: JJ
authors.lastname: Parker
authors.forename: G S
authors.initials: GS
authors.lastname: Sayler
mesh_terms: D000641:Ammonia / Q000378:metabolism; D001419:Bacteria / Q000235:genetics / Q000302:isolation & purification; D018533:Biomass; D019149:Bioreactors; D009606:Nitrosomonas / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D016133:Polymerase Chain Reaction; D011157:Population Dynamics; D014865:Waste Disposal, Fluid; D014872:Water Movements
chemical_list: D000641:Ammonia