Intensifying niacin-based biosynthesis of NAD to enhance 3-hydroxypropionic acid production in Klebsiella pneumoniae.

Objective: Glycerol-based biosynthesis of 3-hydroxypropionic acid (3-HP) in Klebsiella pneumoniae involves two reactions: glycerol conversion to 3-hydroxypropionaldehyde (3-HPA) by glycerol dehydratase, and 3-HPA conversion to 3-HP by aldehyde dehydrogenase (ALDH). The ALDH catalysis consumes a lot of cofactor nicotinamide adenine dinucleotide (NAD), which constrains 3-HP production.

Results: Here we report that intensifying niacin-based biosynthesis of NAD can substantially enhance 3-HP production. We constructed tac promoter-driven NAD synthesis pathway in K. pneumoniae. The strain only overexpressing nicotinate phosphoribosyltransferase (PncB) showed 14.24% increase in the production of NAD relative to the stain harboring an empty vector. When PncB was coexpressed with PuuC (one of native ALDHs), the recombinant strain exhibited increased ALDH activity but slightly reduced 3-HP production due to plasmid burden. When 30 mg niacin l (a substrate for biosynthesis of NAD) was added into shake flask, the strain produced 0.55 g 3-HP l, which was 2.75 times that of the control. In a 5-L bioreactor, replenishment of niacin led to 36.43% increase of 3-HP production.

Conclusions: These results indicated that intensifying niacin-based biosynthesis of NAD boosts 3-HP production.