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Fluorescence in situ hybridization (FISH) was used to analyse the community composition of a sequencing batch reactor (SBR) operating with aerobic-anaerobic cycling and fed acetate as its sole carbon source. Phosphorus was removed from the SBR microbiologically. Marked shifts in the community structure occurred as the phosphorus/carbon (P/C) ratio in the feed was changed. When the P/C ratio was shifted from 1 :10 to 1 :50, FISH analysis showed that the percentage of β-Proteobacteria fell from ca 77 % of the total bacteria to ca 38 %. This decrease in the β-Proteobacteria coincided with a reduction in both the proportions of the β-proteobacterial Rhodocyclus-related phosphorus-accumulating bacteria and the biomass phosphorus content. Both the α-and β-proteobacterial ' G-bacterial ' populations assimilated acetate and synthesized PHA anaerobically. The α-Proteobacteria are considered responsible for glycogen production in these SBR systems.

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Micromanipulation was used to obtain an isolate (BEN 52) of Eikelboom Type 1851 from a bulking activated sludge plant. Its 16S rDNA sequence reveals its closest relative is 'Roseiflexus castenholzii', a member of the phylum 'Chloroflexi', class 'Chloroflexi', previously called the green non-sulfur bacteria. The 16S rRNA targeted oligonucleotide probe designed for fluorescence in situ hybridisation against this sequence successfully identified filamentous bacteria with the morphological features of Type 1851 in activated sludge samples from plants in several countries and different operational configurations.

Activated sludge plants designed to remove phosphorus microbiologically often perform unreliably. One suggestion is that the polyphosphate-accumulating organisms (PAO) are out-competed for substrates by another group of bacteria, the glycogen-accumulating organisms (GAO) in the anaerobic zones of these processes. This study used fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE) to analyse the communities from laboratory-scale anaerobic : aerobic sequencing batch reactors. Members of the genus Sphingomonas in the a-Proteobacteria were present in large numbers in communities with poor phosphorus removal capacity where the biomass had a high glycogen content. Their ability to store poly-b-hydroxyalkanoates anaerobically, but not aerobically, and not accumulate polyphosphate aerobically is consistent with these organisms behaving as GAO there. No evidence was found to support an important role for the c-Proteobacteria as possible GAO in these communities, although these bacterial populations have been considered in other studies to act as possible competitors for the PAO.

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