Specialist Group on Microbial Ecology and Water Engineering - IWA

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THE DEFLUVIICOCCUS-RELATED GLYCOGEN ACCUMULATINGORGANISMS IN ACTIVATED SLUDGE SYSTEMS.Simon J. McIlroy & Tadashi NittamiBiotechnology Research CentreLa Trobe University, Bendigo, 3550, AustraliaOver the past two decades our understanding of the microbiology of enhanced biologicalphosphorus removal (EBPR) has progressed rapidly through the application of cultureindependent molecular methods. It is recognised currently that the organisms responsible,the polyphosphate accumulating organisms (PAO), are phylogenetically diverse, withmembers in the Betaproteobacteria, including ‘Accumulibacter’, and the Actinobacteria,and many studies indicate further, yet to be defined, diversity exists among these PAO.The glycogen accumulating organisms (GAO) are a phenotypically defined groupthought to compete with the PAO for substrates in the anaerobic zone without subsequentuptake of phosphorus in the aerobic zone, thus leading to a potential reduction in theEBPR efficiency. Like the PAO, they appear to be quite diverse phylogenetically. Twomain groups are recognised within the Gamma- and Alphaproteobacteria. Thegammaproteobacterial GAO encompass ‘Competibacter’ related organisms, large coccifound in EBPR systems together with the PAO. This group is quite diverse in itself withseven recognised deeply branched sub-clusters, and indications of further as yetunelucidated phylogenetic lineages (Kong et al., 2006).The alphaproteobacterial GAO include the Defluviicoccus vanus-related organisms,which like the ‘Competibacter’, also appear to be diverse phylogenetically (Fig. 1).Defluviicoccus vanus was first isolated from a plant treating brewery waste and shown toexhibit the GAO phenotype in pure culture. It is still the only known cultured organismsexhibiting the GAO phenotype (Maszenan et al., 2005). The group, whose observedmembers grow in distinctive clusters of four cocci (hence the name ‘tetrad formingorganisms’ (TFO)(see Fig. 2a-c), was recognised in situ first by Wong et al. (2004).Further work by Meyer et al. (2006) with a community fed propionate as sole carbonsource, identified a second group clustering separately from Wong’s previously definedcluster 1 members. Subsequently members of a third cluster, initially proposed by Wong& Liu (2007), have been shown by work in our laboratory (Nittami et al., 2009) to have a‘Nostocoida limicola’-like filamentous morphotype (See Fig 2d-e), and include theuncultured bulking filament previously described as Candidatus ‘Monilibacter batavus’(Fig. 1).More recently we have identified a fourth Defluviicoccus cluster, which like the membersof clusters 1 and 2, share the distinctive TFO morphology (McIlroy and Seviour, InPress) (Fig. 1). It seems likely that more diversity exists among these. Consequently thequestion arises as to whether these cluster 3 and 4 members have a GAO phenotype andpose possible threats to EBPR capacity in P removal activated sludge systems. We havestarted to look at this question. Certainly the filamentous cluster 3 Defluviicoccus arefound as dominant populations in EBPR processes in S.E Australia, but their abundancein such plants globally is unclear. The FISH probes designed and validated by Nittami et_________________________________________________________________________________________________IWA <strong>Specialist</strong> <strong>Group</strong> on: Microbial Ecology and Water Engineering 10Newsletter December 2009
al. (2009) should help resolve this. They also cycle carbon through PHA under aerobic;anaerobic conditions, and are able to assimilate acetate and propionate under anaerobicconditions in biomass samples from EBPR communities. Consequently their phenotype isas expected of GAO (Mino et al., 1998; Seviour and McIlroy, 2008).Fig. 1. Maximum likelihood tree of the ‘complete’ Defluviicoccus –related sequences (≤1250 bp long)(McIlroy and Seviour, In Press). Parsimony bootstrap values are onlyindicated for values ≥ 75 %. ○ indicates a bootstrap value of ≥ 75 % and ● indicates abootstrap value of ≥ 95 %. * Indicates partial sequences added using the ‘quick add’_________________________________________________________________________________________________IWA <strong>Specialist</strong> <strong>Group</strong> on: Microbial Ecology and Water Engineering 11Newsletter December 2009
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