Translocation of Zymomonas mobilis pyruvate decarboxylase to periplasmic compartment for production of acetaldehyde outside the cytosol.

Acetaldehyde, a valuable commodity chemical, is a volatile inhibitory byproduct of aerobic fermentation in Zymomonas mobilis and in several other microorganisms. Attempting to improve acetaldehyde production by minimizing its contact with the cell interior and facilitating its removal from the culture, we engineered a Z. mobilis strain with acetaldehyde synthesis reaction localized in periplasm. For that, the pyruvate decarboxylase (PDC) was transferred from the cell interior to the periplasmic compartment. This was achieved by the construction of a Z. mobilis Zm6 PDC-deficient mutant, fusion of PDC with the periplasmic signal sequence of Z. mobilis gluconolactonase, and the following expression of this fusion protein in the PDC-deficient mutant. The obtained recombinant strain PeriAc, with most of its PDC localized in periplasm, showed a twofold higher acetaldehyde yield, than the parent strain, and will be used for further improvement by directed evolution.