An Aldolase-Based New Pathway for Bioconversion of Formaldehyde and Ethanol into 1,3-Propanediol in .

Formaldehyde (HCHO) is a reactive one-carbon compound that is interesting for biosynthesis. The assimilation of HCHO depends on the catalysis of aldolase. Here, we present a novel synthetic pathway in to convert HCHO and ethanol into 1,3-propanediol (PDO) using a deoxyribose-5-phosphate aldolase (DERA). DERA condenses HCHO and acetaldehyde to form 3-hydroxypropionaldehyde, the direct precursor of PDO formation. This new pathway opens up the possibility to synthesize an appealing C3 compound from a C1 compound and a C2 compound without carbon loss in contrast to all the other known PDO synthetic pathways where typically 30-50% of the carbons are lost as CO and other byproducts. The pathway is successfully demonstrated by elaborating three metabolic modules. First, DERA from was found to be efficient for the aldol condensation and PDO production module. For the module of acetaldehyde supply from ethanol, an alcohol dehydrogenase from was selected. For the HCHO supply module, the control of HCHO concentration and its utilization were shown to be important for achieving the assimilation of HCHO in recombinant cells. By deleting the gene for endogenous conversion of HCHO to formate and controlling HCHO at a level of about 0.6 mM, the concentration and yield of PDO were increased from initially 5.67 mM (0.43 g/L) and 0.057 mol/mol to 17.35 mM (1.32 g/L) and 0.096 mol/mol in bioconversion of ethanol and HCHO with resting cells. Further engineering of DERA and the HCHO supply module is necessary to realize the potential of this promising metabolic pathway.