Genetic approach to enhanced biological phosphorus removal

Genetic improvement of bacterial ability to accumulate phosphate (Pi) was investigated using Escherichia coli as a test organism. High levels of Pi accumulation were achieved by (i) modifying the genetic regulation and increasing the dosage of the E. coli genes encoding polyphosphate kinase ( ppk ), acetate kinase ( ackA ), and the phosphate inducible transport system ( pstS , pstC , pstA , and pstB ) and (ii) genetically inactivating ppx encoding exopolyphosphatase. Acetate kinase was employed as an ATP regeneration system for polyphosphate synthesis. The best recombinant strain, which contained both pBC29 ( ppk ) and pEP02.2 ( pst genes) accumulated approximately 10-fold more Pi than did the control strain. The phosphorus content of this recombinant reached a maximum of 16 % on the dry weight basis (49 % as phosphate). About 65 % of the cellular phosphorus was stored as polyphosphate.