Involvement of Rhodocyclus -Related Organisms in Phosphorus Removal in Full-Scale Wastewater Treatment Plants

Abstract

The participation of organisms related to Rhodocyclus in full-scale enhanced biological phosphorus removal (EBPR) was investigated. By using fluorescent in situ hybridization techniques, the communities of Rhodocyclus-related organisms in two full-scale wastewater treatment plants were estimated to represent between 13 and 18% of the total bacterial population. However, the fractions of these communities that participated in polyphosphate accumulation depended on the type of treatment process evaluated. In a University of Cape Town EBPR process, the percentage of Rhodocyclus-related cells that contained polyphosphate was about 20% of the total bacterial population, but these cells represented as much as 73% of the polyphosphate-accumulating organisms (PAOs). In an aerated-anoxic EBPR process, Rhodocyclus-related PAOs were less numerous, accounting for 6% of the total bacterial population and 26% of the total PAO population. In addition, 16S ribosomal DNA sequences 99.9% similar to the sequences of Rhodocyclus-related organisms enriched in acetate-fed bench-scale EBPR reactors were recovered from both full-scale plants. These results confirmed the involvement of Rhodocyclus-related organisms in EBPR and demonstrated their importance in full-scale processes. In addition, the results revealed a significant correlation between the type of EBPR process and the PAO community.Phosphorus removal from wastewater can be accomplished biologically in activated sludge reactors by incorporating an anaerobic stage prior to existing aerobic basins (10). The resulting cyclic anaerobic and aerobic conditions favor the growth of microorganisms that utilize intracellular polyphosphate as an energy source during the anaerobic period, which allows them to sequester available carbon for use during the following aerobic stage (18). In turn, the aerobic utilization of intracellular stored carbon is accompanied by the uptake of phosphorus and accumulation of phosphorus as polyphosphate. This polyphosphate accumulation results in efficient removal of phosphorus from the wastewater. Although this process, termed enhanced biological phosphorus removal (EBPR), has been used successfully in full-scale wastewater treatment plants (WWTPs), identification and characterization of the industrially relevant organisms that are involved in phosphate uptake have proven to be difficult (18). In the initial attempts to identify polyphosphate-accumulating organisms (PAOs) the workers used enrichment cultures and traditional culturing approaches (5, 9, 16, 25). However, the microorganisms recovered (predominantly Acinetobacter sp.) did not exhibit all the biochemical characteristics believed to be required for cyclic phosphate uptake and release and were later shown, by a variety of culture-independent methods, to be minor components of the microbial communities in full-scale EBPR processes (4,6,12,13,23). Recently, working with acetate-fed laboratory-scale reactors, Hesselmann et al. (11) and Crocetti et al. (7) provided evidence that when an organism cl...

Are some putative glycogen accumulating organisms (GAO) in anaerobic : aerobic activated sludge systems members of the α-Proteobacteria?

“…The availability of the FISH probe sequences for the SBR9-1 clone should now provide the opportunity to determine how widespread these a-Proteobacteria are, especially in full-scale plants where this study has shown they may exist, and whether, for example, they are the same or similar populations to the a-Proteobacteria seen in high numbers by Crocetti et al (2002) in their community. However, it may be that these GAO do not always store glycogen under all conditions, which now seems to be the case with polyP and the Rhodocyclus-related PAO (Wagner & Loy, 2002;Zilles et al, 2002). If so, this will further complicate attempts to relate numerical dominance of particular morphotypes to their functional roles in biomasses displaying deteriorated EBPR.…”

A bacterial metapopulation adapts locally to phage predation despite global dispersal

“…To date, CAP has only been detected in activated sludges (Hesselmann et al 1999;Crocetti et al 2000;Zilles et al 2002;Wong et al 2005), which are sparse and tiny microbial reservoirs on a global scale and have only been in operation for about a century (Tchobanoglous et al 2003). The relatively recent introduction of activated sludge systems suggests that CAP originated and therefore is able to survive in alternative environments.…”

Identity and Ecophysiology of Uncultured Actinobacterial Polyphosphate-Accumulating Organisms in Full-Scale Enhanced Biological Phosphorus Removal Plants

“…RPAO were able to grow and take up P i with oxygen, nitrate, or nitrite present as an electron acceptor, strongly suggesting that they are able to denitrify while taking up P i . Recent FISH investigations of their occurrence in full-scale EBPR plants suggest that these bacteria are generally abundant and thus important PAO (8,15,39).Some bacteria belonging to the gram-positive Actinobacteria have also been suggested to be potential PAO because some isolates have demonstrated aerobic P i uptake ability after taking up organic substrates under anaerobic conditions (34). These bacteria include Microlunatus phosphovorus (32) and Tetrasphaera elongata (strain ASP12) (29).…”