Engineering <i>Escherichia coli</i> for <scp>d</scp>-Allulose Production from <scp>d</scp>-Fructose by Fermentation

Abstract

d-Allulose is considered an ideal alternative to sucrose and has shown tremendous application potential in many fields. Recently, most efforts on production of d-allulose have focused on <i>in vitro</i> enzyme-catalyzed epimerization of cheap hexoses. Here, we proposed an approach to efficiently produce d-allulose through fermentation using metabolically engineered <i>Escherichia coli</i> JM109 (DE3), in which a SecY (ΔP) channel and a d-allulose 3-epimerase (DPEase) were co-expressed, ensuring that d-fructose could be transported in its nonphosphorylated form and then converted into d-allulose by cells. Further deletion of <i>fruA</i>, <i>manXYZ</i>, <i>mak</i>, <i>galE</i>, and <i>fruK</i> and the use of Ni²⁺ in a medium limited the carbon flux flowing into the byproduct-generating pathways and the Embden-Meyerhof-Parnas (EMP) pathway, achieving <i>a</i> ≈ 0.95 g/g yield of d-allulose on d-fructose using <i>E. coli</i> (DPEase, SecY [ΔP], ΔFruA, ΔManXYZ, ΔMak, ΔGalE, ΔFruK) and 8 μM Ni²⁺. In fed-batch fermentation, the titer of d-allulose reached ≈23.3 g/L.