Simultaneous expression of glutaryl-7-aminocephalosporanic acid acylase gene and lysis genes of phage λ in a recombinant E. coli

Abstract

Glutaryl-7-aminocephalosporanic acid acylase (GLA), recommended for use in the form of immobilized-enzyme, is one of the two key enzymes in the two-step synthesis of 7-aminocephalosporanic acid. For simplifying the process of cell disruption and immobilization, the lysis genes of phage λ ( S − RRz) with the S amber mutation were designed to introduce into the over-expression system of GLA. A novel recombinant strain, E. coli TB1/pMKC- AS, simultaneously containing the maltose binding protein gene ( malE), the lysis genes ( S − RRz) and the target GLA gene ( Acy) in a same operon, was successfully constructed. Under neutral pH conditions, cell growth and GLA activity of TB1/pMKC- AS was not affected by the presence of the lysis genes, however, autolysis phenomenon was observed under weak alkaline conditions. Through pH control and fed-batch culture, the GLA activity of TB1/pMKC- AS reached as high as 6810 U/L with 24.8 g/L dry cell density (OD 600 = 67.9) in a 5 L fermentor. In contrast to the cells of E. coli TB1/pMKC- Acy without the lysis genes, the mild EDTA/Tris buffer (pH 8.0) can cause the lysis of the cells of TB1/pMKC- AS containing the lysis genes. Correspondingly, a mild pH 9.0/42 °C incubation method was developed for conveniently degrading the recombinant cells of TB1/pMKC- AS, based on the expression of the lysis genes. Further experiments showed that the cell lysate after the mild incubation disruption can be directly immobilized by 10% polyacrylamide to make the immobilized enzymes. In comparison with the immobilized GLA from TB1/pMKC- Acy, the immobilized cell lysate of TB1/pMKC- AS has the similar characteristics of catalysis stability, implying a great potential for industrial application of the lysis genes-assisted cell disruption.