Recent developments in the biochemistry and ecology of enhanced biologicalphosphorus removal

Most of the genes encoding the enzymes involved in polyP synthesis and degr adation and in phosphate transport have been studied in various Gram-negati ve bacteria. Progress has also been made in studying the biochemical mechan isms underlying the process of enhanced biological phosphorus removal (EBPR ), in particular in lab-scale systems fed with acetate or acetate plus gluc ose as the sole carbon and energy sources. By applying C-13-NMR, previous m odels concerning anaerobic carbon metabolism have been advanced and the rol e of glycogen in providing reducing equivalents in EBPR is definitely demon strated. The role of the citric acid cycle in supplying reducing equivalent s for the conversion of acetyl-CoA into poly-beta-hydroxybutyrate and poly- beta-hydroxyvalerate has been discussed, an incomplete citric acid cycle ha s been proposed to provide a small part of the reducing equivalents. Polyph osphate:AMP phosphotransferase and polyphosphatase were readily detectable in EBPR sludge fed with acetate plus glucose, but polyphosphate kinase rema ined undetected. In a lab-scale EBPR system, fed for several months with on ly acetate as carbon source, a Rhodocyclus-like bacterium (R6) was highly e nriched and is therefore probably responsible for EBPR in systems fed with acetate only. This R6-type bacterium was however also present in other EBPR sludges (but to a lesser extent), and may therefore play an important role in EBPR in general. This organism accumulates polyhydroxyalkanoates anaero bically and polyp under aerobic conditions. Unlike members of the genus Rho docyclus bacterium R6 cannot grow phototrophically, Therefore a provisional new genus Candidatus and species Accumulibacter phosphatis was proposed.