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.