Most of the genes encoding the
enzymes involved in
polyP synthesis and degradation and in
phosphate transport have been studied in various Gram-negative bacteria. Progress has also been made in studying the biochemical mechanisms underlying the process of enhanced
biological phosphorus removal (EBPR), in particular in lab-scale systems fed with
acetate or
acetate plus
glucose as the sole
carbon and energy sources. By applying 13C-NMR, previous models concerning anaerobic
carbon metabolism have been advanced and the role of
glycogen in providing reducing equivalents in EBPR is definitely demonstrated. The role of the citric acid cycle in supplying reducing equivalents for the conversion of
acetyl-CoA into
poly-beta-hydroxybutyrate and poly-beta-hydroxyvalerate has been discussed. An incomplete citric acid cycle has been proposed to provide a small part of the reducing equivalents.
Polyphosphate:AMP phosphotransferase and
polyphosphatase were readily detectable in EBPR sludge fed with
acetate plus
glucose, but
polyphosphate kinase remained undetected. In a lab-scale EBPR system, fed for several months with only
acetate as
carbon source, a Rhodocyclus-like bacterium (R6) was highly enriched 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 anaerobically and
polyP under aerobic conditions. Unlike members of the genus Rhodocyclus, bacterium R6 cannot grow phototrophically. Therefore a provisional new genus Candidatus and species Accumulibacter phosphatis was proposed.