Genetic improvement of Escherichia coli for enhanced biological removal of phosphate from wastewater

Abstract

The ability of Escherichia coli MV1184 to accumulate inorganic phosphate (P1) was enhanced by manipulating the genes involved in the transport and metabolism of P1. The high-level P1 accumulation was achieved 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 either pBC29 (carrying ppk) or pEP02.2 (pst operon), removed approximately two and threefold, respectively, more P1 from minimal medium than did the control strain. The highest rates of P1 removal were obtained by strain MV1184 containing pEP03 (ppk and ackA). However, unlike the control strain, MV1184(pEP03) released P1 to the medium after growth had stopped. Drastic changes in growth and P1 uptake were observed when pBC29 (ppk) and pEP02.2 (pst operon) were introduced simultaneously into MV1184. Even though growth of this recombinant was severely limited in minimal medium, the recombinant could remove approximately threefold more P1 than the control strain. Consequently, the phosphorus content of this recombinant reached a maximum of approximately 16% on a dry weight basis (49% as phosphate).