Fig. 5

The HPLC analysis and identification of 4-HBA produced in strain Δ7-HBA. a HPLC spectrum at 201 nm of the 4-HBA standard and fermentation supernatant of the strains S. cerevisiae aro7Δ and Δ7-HBA (with genes of ARO2, ARO1, ARO4^K229L, ubiC^syn, ppsA and ktA integrated into δ sites of S. cerevisiae aro7Δ). b Mass spectrum of peak I in the fermentation supernatant of Δ7-HBA, which was collected and analyzed by LC–MS in negative ion mode in a methanol–water (containing 20 mM NH₄Ac) gradient system