Enhanced L-phenylalanine production by recombinant Escherichia coli BR-42 (pAP-B03) resistant to bacteriophage BP-1 via a two-stage feeding approach.

The L-phenylalanine (L-Phe) production by Escherichia coli WSH-Z06 (pAP-B03) was frequently prevented by bacteriophage BP-1 infestation. To cope with the bacteriophage BP-1 problem for an improved L-Phe production, one bacteriophage BP-1-resistant mutant, E. coli BR-42, was obtained from 416 mutant colonies of E. coli WSH-Z06 after N-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutagenesis by selection for resistance to bacteriophage BP-1. The recombinant E. coli BR-42-carrying plasmid pAP-B03 had a high capacity in L-Phe production and a remarkable tolerance to 1 × 10(10) pfu (plaque-forming unit)/ml bacteriophage stock. For an enhanced L-Phe production by E. coli BR-42 (pAP-B03), the effects of different feeding strategies including pH-stat, constant rate feeding, linear decreasing rate feeding, and exponential feeding on L-Phe production were investigated; and a two-stage feeding strategy, namely exponential feeding at μ (set) = 0.18 h(-1) in the first 20 h and a following linear varying rate feeding with F = (-0.55 × t + 18.6) ml/h, was developed to improve L-Phe production. With this two-stage feeding approach, a maximum L-Phe titer of 57.63 g/l with a high L-Phe productivity (1.15 g/l/h) was achieved, which was 15% higher than the highest level (50 g/l) reported so far according to our knowledge. The recombinant E. coli BR-42 (pAP-B03) is a potential L-Phe over-producer in substantial prevention of bacteriophage BP-1 infestation compared to its parent strain WSH-Z06 (pAP-B03).