Comparison of acetate and propionate uptake by polyphosphate accumulating organisms and glycogen accumulating organisms

Abstract

Enhanced biological phosphorus removal (EBPR) performance is directly affected by the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). This study investigates the effects of carbon source on PAO and GAO metabolism. Enriched PAO and GAO cultures were tested with the two most commonly found volatile fatty acids (VFAs) in wastewater systems, acetate and propionate. Four sequencing batch reactors (SBRs) were operated under similar conditions and influent compositions with either acetate or propionate as the sole carbon source. The stimulus for selection of the PAO and GAO phenotypes was provided only through variation of the phosphorus concentration in the feed. The abundance of PAOs and GAOs was quantified using fluorescence in situ hybridisation (FISH). In the acetate fed PAO and GAO reactors, "Candidatus Accumulibacter phosphatis" (a known PAO) and "Candidatus Competibacter phosphatis" (a known GAO) were present in abundance. A novel GAO, likely belonging to the group of Alphaproteobacteria, was found to dominate the propionate fed GAO reactor. The results clearly show that there are some very distinctive differences between PAOs and GAOs in their ability to take up acetate and propionate. PAOs enriched with acetate as the sole carbon source were immediately able to take up propionate, likely at a similar rate as acetate. However, an enrichment of GAOs with acetate as the sole carbon source took up propionate at a much slower rate (only about 5% of the rate of acetate uptake on a COD basis) during a short-term switch in carbon source. A GAO enrichment with propionate as the sole carbon source took up acetate at a rate that was less than half of the propionate uptake rate on a COD basis. These results, along with literature reports showing that PAOs fed with propionate (also dominated by Accumulibacter) can immediately switch to acetate, suggesting that PAOs are more adaptable to changes in carbon source as compared to GAOs. This study suggests that the PAO and GAO competition could be influenced in favour of PAOs through the provision of propionate in the feed or even by regularly switching the dominant VFA species in the wastewater. Further study is necessary in order to provide greater support for these hypotheses.

Anaerobic and aerobic metabolism of glycogen-accumulating organisms selected with propionate as the sole carbon source

“…Recent studies have suggested that a propionate feed source is more beneficial for reliable EBPR performance than acetate (Chen et al, 2004;Oehmen et al, 2005aOehmen et al, , 2006Pijuan et al, 2004;Thomas et al, 2003), likely due to a reduced level of GAO activity. The metabolic activity of PAOs and GAOs fed with different carbon sources is compared in Further investigation is required to assess the proliferation of these Alphaproteobacteria GAOs in EBPR plants as well as their ability to compete with PAOs in these systems.…”

“…Accumulibacter appears to be a dominant PAO in the presence of both acetate and propionate as carbon sources, and has been shown to have the capacity to switch between acetate and propionate uptake without the need for acclimation (Oehmen et al, 2005a;Pijuan et al, 2004). It is possible, however, that GAOs have a more specific preference for acetate or propionate.…”

“…It is possible, however, that GAOs have a more specific preference for acetate or propionate. In one study, GAOs enriched with acetate as the sole carbon source (and dominated by Competibacter) were shown to be far less effective in propionate uptake, while GAOs enriched with propionate (dominated by Alphaproteobacteria) were shown to take up acetate at less than half the rate of propionate (Oehmen et al, 2005a). A carbon source preference exhibited by different groups of GAOs could perhaps be useful in minimizing the undesirable proliferation of GAOs in EBPR systems.…”

“…These organisms have been called either 'Candidatus Competibacter phosphatis' (henceforth called Competibacter; Crocetti et al, 2002) or the GB lineage . Competibacter can consume acetate as the sole carbon source, but a recent study has shown that they take up propionate very slowly (Oehmen et al, 2005a), and thus tend to be out-competed by Accumulibacter (Oehmen et al, 2005a(Oehmen et al, , 2006Pijuan et al, 2004).…”

Abundance and ecophysiology of Defluviicoccus spp., glycogen-accumulating organisms in full-scale wastewater treatment processes

“…GAOs also take up and store organic carbon under anaerobic conditions but do not cycle P i (anaerobic release and aerobic uptake), and their selective enrichment over PAOs via competition for sparingly available VFAs in EBPR plants leads to excessive P i in plant effluents (Liu et al, 1996;Mino et al, 1995). Lab-scale (Bond et al, 1999;Oehmen et al, 2005) and full-scale (Kong et al, , 2006Saunders et al, 2003) EBPR studies showed this PAO-GAO competition for VFAs. Pure cultures that display the PAO or GAO phenotype as described above have not yet been acquired Seviour et al, 2003).…”