Applied and Environmental Microbiology, March 2000, p. 1175-1182, Vol. 66, No. 3
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Department of Microbiology and Parasitology1 and Department of Chemical Engineering,3 Advanced Wastewater Management Centre, The University of Queensland, St. Lucia, 4072 Queensland, Australia, and Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720-17102
Received 9 August 1999/Accepted 23 November 1999
Laboratory-scale sequencing batch reactors (SBRs) as models for
activated sludge processes were used to study enhanced biological phosphorus removal (EBPR) from wastewater. Enrichment for
polyphosphate-accumulating organisms (PAOs) was achieved
essentially by increasing the phosphorus concentration in the influent
to the SBRs. Fluorescence in situ hybridization (FISH) using domain-,
division-, and subdivision-level probes was used to assess the
proportions of microorganisms in the sludges. The A sludge, a
high-performance P-removing sludge containing 15.1% P in the
biomass, was comprised of large clusters of
polyphosphate-containing coccobacilli. By FISH, >80%
of the A sludge bacteria were
-2 Proteobacteria arranged
in clusters of coccobacilli, strongly suggesting that
this group contains a PAO responsible for EBPR. The second dominant
group in the A sludge was the Actinobacteria. Clone
libraries of PCR-amplified bacterial 16S rRNA genes from three
high-performance P-removing sludges were prepared, and clones belonging
to the
-2 Proteobacteria were fully sequenced. A
distinctive group of clones (sharing
98% sequence identity) related
to Rhodocyclus spp. (94 to 97% identity) and
Propionibacter pelophilus (95 to 96% identity) was
identified as the most likely candidate PAOs. Three probes specific for
the highly related candidate PAO group were designed from the sequence data. All three probes specifically bound to the morphologically distinctive clusters of PAOs in the A sludge, exactly coinciding with the
-2 Proteobacteria probe. Sequential FISH and
polyphosphate staining of EBPR sludges clearly demonstrated
that PAO probe-binding cells contained polyphosphate.
Subsequent PAO probe analyses of a number of sludges with various P
removal capacities indicated a strong positive correlation between P
removal from the wastewater as determined by sludge P content and
number of PAO probe-binding cells. We conclude therefore that an
important group of PAOs in EBPR sludges are bacteria closely related to
Rhodocyclus and Propionibacter.
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