Externally Supplied Mannitol and Trehalose Boost Phloroglucinol Biosynthesis in Escherichia coli

Biosynthesis of phloroglucinol, an important polyketide compound, has been achieved in engineered Escherichia coli . However, the high level of inherent phloroglucinol toxicity impairs the growth of the producing strains and reduces the efficiency of this bioprocess. It was hypothesized that suitable protective agents might reduce the inhibitory effects. In this study, 4 protective agents including betaine, mannitol, proline, and trehalose with concentrations at a range of 0–1.0 g/L were examined. The results demonstrated that mannitol and trehalose could protect the producing strains against high level of phloroglucinol stress and boost the biosynthesis of phloroglucinol in the recombinant strains in a dose-dependent manner, while betaine and proline showed little positive effect. Mannitol and trehalose (1.0 g/L) increased the phloroglucinol titer from 0.75 ± 0.01 to 0.89 ± 0.03 and 0.96 ± 0.04 g/L, respectively. The protective mechanisms of mannitol and trehalose were also investigated. It was found that the toxicity of high concentration of phloroglucinol was related to reactive oxygen species and that exogenous mannitol and trehalose could increase the activity of superoxide dismutase while showed little effect on catalase.