(257h) Metabolic Engineering of Propionibacteria for n-Propanol Production

Propionibacteria are widely used in industry for manufacturing of Swiss cheese, vitamin B12 and propionic acid. Little is known about their genetics and only a few reports are available on their metabolic engineering. Most previous metabolic engineering work on propionibacteria aimed at improving the fermentative production of either vitamin B12 or propionic acid. n-Propanol is a common solvent, intermediate in many industrial applications and a promising biofuel. No known microorganism can produce n-propanol naturally in sufficient quantities for manufacturing purposes. In this research, a bifunctional alcohol aldehyde deydrogenase (aad) was cloned from E. coli and overexpressed in propionibacteria. The mutant expressing the aad gene produced n-propanol from propionyl-CoA, which is the precursor for propionic acid biosynthesis. The production of n-propanol was limited by available NADH, which was improved significantly by using a mixture of different carbon sources. To our best knowledge, this is the first report on producing n-propanol by metabolically engineered propionibacteria, which offers a novel route to produce n-propanol from biomass.