Inhibition of Anaerobic Phosphate Release by Nitric Oxide in Activated Sludge

Abstract

Activated sludge not containing significant numbers of denitrifying, polyphosphate [poly(P)]-accumulating bacteria was grown in a fill-and-draw system and exposed to alternating anaerobic and aerobic periods. During the aerobic period, poly(P) accumulated up to 100 mg of P · g of (dry) weight. When portions of the sludge were incubated anaerobically in the presence of acetate, 80 to 90% of the intracellular poly(P) was degraded and released as orthophosphate. Degradation of poly(P) was mainly catalyzed by the concerted action of polyphosphate:AMP phosphotransferase and adenylate kinase, resulting in ATP formation. In the presence of 0.3 mM nitric oxide (NO) in the liquid-phase release of phosphate, uptake of acetate, formation of poly-β-hydroxybutyrate, utilization of glycogen, and formation of ATP were severely inhibited or completely abolished. In cell extracts of the sludge, adenylate kinase activity was completely inhibited by 0.15 mM NO. The nature of this inhibition was probably noncompetitive, similar to that with hog adenylate kinase. Activated sludge polyphosphate glucokinase was also completely inhibited by 0.15 mM NO. It is concluded that the inhibitory effect of NO on acetate-mediated phosphate release by the sludge used in this study is due to the inhibition of adenylate kinase in the phosphate-releasing organisms. The inhibitory effect of nitrate and nitrite on phosphate release is probably due to their conversion to NO. The lack of any inhibitory effect of NO on adenylate kinase of the poly(P)-accumulatingAcinetobacter johnsonii 210A suggests that this type of organism is not involved in the enhanced biological phosphate removal by the sludges used.

The microbiology of biological phosphorus removal in activated sludge systems

“…The presence of nitrate is thought to provide denitrifying bacteria with an opportunity to remove the selective advantage the PAO have in these systems by out-competing them for the metabolizable substrates available there [159^163]. However, the inhibitory e¡ect of nitrate may be more direct because nitric oxide, an intermediate in denitri¢cation has been shown to prevent anaerobic P release in EBPR sludge by inhibiting the adenylate kinase (see Section 14) involved in polyP degradation [164].…”

Research Advances and Challenges in the Microbiology of Enhanced Biological Phosphorus Removal—A Critical Review

“…The assumption that PAOs are less capable of nitrate reduction also led to the exclusion of denitrification from early EBPR models Wentzel, Ekama, Loewenthal, Dold, and Marais, 1989). Poor phosphorus removal under nitrate-rich conditions in the anaerobic zone has been attributed to the disruption of anaerobic conditions by nitrate (Barnard, 1976), consumption of fatty acids by denitrifying non-polyphosphate heterotrophs (Barker and Dold, 1996;Hascoet and Florentz, 1985b), and inhibition of PAOs by nitrite, as a result of incomplete denitrification (Ahn et al, 2001;Hu et al, 2003;Jiang et al, 2006;Meinhold, Arnold, and Isaacs, 1999;Saito et al, 2004;van Niel et al, 1998;Zhou et al, 2007).…”

Impact of solid residence time (SRT) on functionally relevant microbial populations and performance in full‐scale enhanced biological phosphorus removal (EBPR) systems

“…Another aspect worthy of mentioning is that, despite the presence of nitrate at the beginning of most batch testing (ranging from 8.1 to 15 mg/L), P release occurred simultaneously without any delays (Supporting Information Figure ). Several studies have shown that nitrate has a negative effect on the EBPR performance during the anaerobic phase, due to the competition for carbon between the denitrifying population and the PAOs (López‐Vázquez et al, ; Yagci, Artan, Çokgör, Randall, & Orhon, ), and possible inhibitory effect of nitric oxide produced during denitrification (Van Niel, Appeldoorn, Zehnder, & Kortstee, ). The results of this study showed that the presence of nitrate did not seem to significantly affect the P release rate.…”