Constructing an efficient salicylate biosynthesis platform by Escherichia coli chromosome integration.

Salicylate (SA) is an important platform chemical widely used in cosmetic and pharmaceutical industries. In this study, an efficient SA producing strain was constructed by step-by-step chromosome integration. First, the SA biosynthetic module controlled by promoters PT7 or Ptac was integrated into the chromosome of E. coli, generating the basal strain SA producing strains. PT7 performed better than Ptac and led to higher SA titers, the best of which was 233.6 ± 6.6 mg/L. Disrupting pheA/tyrA eliminated accumulation of phenylalanine and tyrosine, improving SA titer to 492.4 ± 9.3 mg/L. Strengthening the upstream pathway by enhancing expression of aroG further improved SA titer to 679.9 ± 27.1 mg/L. Furthermore, pykA/pykF were disrupted to conserve phosphoenolpyruvate, resulting in a final strain that can produce 769.8 ± 12.6 mg/L of SA using glucose and glycerol as the mixed carbon source. When using sole glycerol instead, the titer was significantly improved to 1560.6 ± 50.2 mg/L. The platform strain was further used to produce muconic acid and salicyl alcohol by introducing the downstream SA-conversion modules. In this study, we constructed an effcient SA producing E. coli strain by chromosome integration, which can be used as a platform for the production of SA derivatives.