Effect of Salt on the Metabolism of ‘Candidatus Accumulibacter’ Clade I and II

Abstract

Saline wastewater is known to affect the performance of phosphate-accumulating organisms (PAOs) in enhanced biological phosphorus removal (EBPR) process. However, studies comparing the effect of salinity on different PAO clades are lacking. In this study, ‘Candidatus Accumulibacter phosphatis’ Clade I and II (hereafter referred to as PAOI and PAOII) were highly enriched (∼90% in relative abundance as determined by quantitative FISH) in the form of granules in two sequencing batch reactors. Anaerobic and aerobic batch experiments were conducted to evaluate the effect of salinity on the kinetics and stoichiometry of PAOI and PAOII. PAOI and PAOII communities showed different priority in using polyphosphate (poly-P) and glycogen to generate ATP in the anaerobic phase when exposed to salt, with PAOI depending more on intracellular poly-P degradation (e.g., the proportion of calculated ATP derived from poly-P increased by 5–6% at 0.256 mol/L NaCl or KCl) while PAOII on glycolysis of intracellularly stored glycogen (e.g., the proportion of calculated ATP derived from glycogen increased by 29–30% at 0.256 mol/L NaCl or KCl). In the aerobic phase, the loss of phosphate uptake capability was more pronounced in PAOII due to the higher energy cost to synthesize their larger glycogen pool compared to PAOI. For both PAOI and PAOII, aerobic conversion rates were more sensitive to salt than anaerobic conversion rates. Potassium (K+) and sodium (Na+) ions exhibited different effect regardless of the enriched PAO culture, suggesting that the composition of salt is an important factor to consider when studying the effect of salt on EBPR performance.

Critical Review of Polyphosphate and Polyphosphate Accumulating Organisms for Agricultural Water Quality Management

“…For marine environments, we found 268 articles in Web of Science that included the keyword “polyphosphate” and 15 articles that included the keyword “polyphosphate accumulating organisms” (Figure , Figure S4, Table S2). Several of the PAO articles discussed the impact of salinity on EBPR processes . As a comparison to other keyword searches in the marine category, there were 9356 articles that included the keyword “phosphorus” and 757 articles that included the keyword “microbiology” (Figure , Figure S4, Table S2).…”

“…Several of the PAO articles discussed the impact of salinity on EBPR processes. 189 As a comparison to other keyword searches in the marine category, there were 9356 articles that included the keyword "phosphorus" and 757 articles that included the keyword "microbiology" (Figure 2, Figure S4, Table S2). By looking more closely at metaanalysis results within the marine category, we found that most polyP and PAO articles were associated with "marine" and "saltwater" keywords rather than "ocean" (Figure S4C, D).…”

Salinity effects on biological treatments

“…The accumulation of nitrite causes a decrease of both phosphate release and uptake rates during aerobic/anoxic and anaerobic phases, respectively (He et al, 2019). This decrease is lower when the process takes place under anoxic conditions due to the capability of PAOs to use nitrite as an electron acceptor (Wang et al, 2018). Suppression of nitrification, or even a low presence of nitrite during nitrification, reduces the negative effect of salinity, but NaCl itself still leads to a partial or total decrease in PAO activity even when long operational periods, to promote a possible biomass acclimation, or inocula from seawater are used (He et al, 2019;Jiang et al, 2018;Pronk et al, 2014;Sharrer et al, 2007;Wang et al, 2017b).…”

“…Suppression of nitrification, or even a low presence of nitrite during nitrification, reduces the negative effect of salinity, but NaCl itself still leads to a partial or total decrease in PAO activity even when long operational periods, to promote a possible biomass acclimation, or inocula from seawater are used (He et al, 2019;Jiang et al, 2018;Pronk et al, 2014;Sharrer et al, 2007;Wang et al, 2017b). These research works showed discrepancies in the inhibition degree caused by NaCl, which could be related to the PAO clades present in the different experiments (Wang et al, 2018), but all of them reported a decrease of PAO activity of approximately 30-40% from concentrations of 5-10 g NaCl/L. Thus, salt inhibition effects seem to be more pronounced on PAOs than on microorganisms involved in organic matter and nitrogen removal processes, probably because PAOs are more sensitive to osmotic pressure .…”

Critical Review of Polyphosphate and Polyphosphate Accumulating Organisms for Agricultural Water Quality Management

“…Several of the PAO articles discussed the impact of salinity on EBPR processes (e.g., Wang et al, 2018) As a comparison to other keyword searches in the marine category, there were 9,356 articles that included the keyword "phosphorus" and 757 articles that included the keyword "microbiology" (Figures 2, S4, Table S2). By looking more closely at meta-analysis results within the marine category, we found that most polyP and PAO articles were associated with "marine" and "saltwater" keywords rather than "ocean" (Figures S4C, S4D).…”