Secretory Production of Recombinant Protein by a High Cell Density Culture of a Protease Negative Mutant Escherichia coli Strain

Several protease negative mutant strains including HM114, HM126, and HM130 as well as their parent strain KS272 were compared for their growth and secretory production of a model fusion protein, protein A(beta)-lactamase. HM114, a strain deficient in two cell envelope proteases, grew slightly faster and produced more fusion protein than the other strains deficient in more proteases. HM114 was grown to a cell dry weight of 47.86 g/L in 29 h using pH-stat, fed-batch cultivation. The (beta)-lactamase activity was 11.25 * 10^4 U/L, which was 30% higher than that obtained with its parent strain KS272. Up to 96% of protein A(beta)-lactamase fusion protein could be recovered by a simple cold osmotic shock method. The specific (beta)-lactamase activity obtained with HM114 after fractionation was 4.5 times higher than that obtained with KS272.