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Background  The biosynthesis of high value-added compounds using metabolically engineered strains has received wide attention in recent years. Myo-inositol (inositol), an important compound in the pharmaceutics, cosmetics and food industries, is usually produced from phytate via a harsh set of chemical reactions. Recombinant  Escherichia coli  strains have been constructed by metabolic engineering strategies to produce inositol, but with a low yield. The proper distribution of carbon flux between cell growth and inositol production is a major challenge for constructing an efficient inositol-synthesis pathway in bacteria. Construction of metabolically engineered  E. coli  strains with high stoichiometric yield of inositol is desirable.    Results  In the present study, we designed an inositol-synthesis pathway from glucose with a theoretical stoichiometric yield of 1 mol inositol/mol glucose. Recombinant  E. coli  strains with high stoichiometric yield (> 0.7 mol inositol/mol glucose) were obtained. Inositol was successfully biosynthesized after introducing two crucial enzymes: inositol-3-phosphate synthase (IPS) from  Trypanosoma brucei , and inositol monophosphatase (IMP) from  E. coli . Based on starting strains  E. coli  BW25113 (wild-type) and SG104 ( ΔptsG::glk ,  ΔgalR::zglf ,  ΔpoxB::acs ), a series of engineered strains for inositol production was constructed by deleting the key genes  pgi ,  pfkA  and  pykF . Plasmid-based expression systems for IPS and IMP were optimized, and expression of the gene  zwf  was regulated to enhance the stoichiometric yield of inositol. The highest stoichiometric yield (0.96 mol inositol/mol glucose) was achieved from recombinant strain R15 (SG104,  Δpgi ,  Δpgm , and RBSL5-zwf). Strain R04 (SG104 and  Δpgi ) reached high-density in a 1-L fermenter when using glucose and glycerol as a mixed carbon source. In scaled-up fed-batch bioconversion in situ using strain R04, 0.82 mol inositol/mol glucose was produced within 23 h, corresponding to a titer of 106.3 g/L (590.5 mM) inositol.    Conclusions  The biosynthesis of inositol from glucose in recombinant  E. coli  was optimized by metabolic engineering strategies. The metabolically engineered  E. coli  strains represent a promising method for future inositol production. This study provides an essential reference to obtain a suitable distribution of carbon flux between glycolysis and inositol synthesis.

Efficient production of myo-inositol in Escherichia coli through metabolic engineering