GENETIC-IMPROVEMENT OF ESCHERICHIA-COLI FOR ENHANCED BIOLOGICAL REMOVAL OF PHOSPHATE FROM WASTE-WATER

The ability of Escherichia coli MV1184 to accumulate inorganic phospha te (P(i)) was enhanced by manipulating the genes involved in the trans port and metabolism of P(i). The high-level P(i) accumulation was achi eved by 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). Acetate kinase was employed as an ATP regeneration system for polyphosphate synthesis. Recombinant strains, which contained eit her pBC29 (carrying ppk) or pEP02.2 (pst operon), removed approximatel y two- and threefold, respectively, more P(i) from minimal medium than did the control strain. The highest rates of P(i) removal were obtain ed by strain MV1184 containing pEP03 (ppk and ackA). However, unlike t he control strain, MV1184(pEP03) released P(i) to the medium after gro wth had stopped. Drastic changes in growth and P(i) uptake were observ ed when pBC29 (ppk) and pEP02.2 (pst operon) were introduced simultane ously into MV1184. Even though growth of this recombinant was severely limited in minimal medium, the recombinant could remove approximately threefold more P(i) than the control strain. Consequently, the phosph orus content of this recombinant reached a maximum of approximately 16 % on a dry weight basis (49% as phosphate).