Co-Production of 3-Hydroxypropionic Acid and 1,3-Propanediol Using Glycerol By Klebsiella Pneumoniae J2B: Reduction of Carbon Traffic at Pyruvate Node
Microbial production of 3-hydroxypropionic acid (3-HP) using glycerol is a two-step reaction involving glycerol dehydratase (GDHt) and aldehyde dehydrogenase (ALDH). GDHt requires coenzyme B12 and ALDH requires NAD+ as cofactors for the production of 3-HP from glycerol. Regeneration of NAD+ requires high aeration which will in turn inhibit GDHt stability and coenzyme B12 production. Also, the imbalance between GDHt and ALDH activities cause the accumulation of toxic intermediate, 3-hydroxypropionaldehyde (3-HPA). As a solution to these problems, co-production of 1,3-propanediol (1,3-PDO) along with 3-HP has been suggested. 1,3-PDO production could regenerate NAD+ and utilize 3-HPA, thus avoiding 3-HPA accumulation and also facilitate the process to be performed under microaerobic conditions. To this end, co-production of 3-HP and 1,3-PDO was attempted in Klebsiella pneumoniae, the natural producer of 1,3-PDO. K. pneumoniaecould coproduce 3-HP and 1,3-PDO successfully but still the process was inefficient in terms of titer and productivity in the later stages. The strain also accumulated huge amounts of acetate and lactate which could reduce the co-production. Especially, acetate accumulation was reported to inhibit the cell performance even at 0.5 g/L by decreasing biomass formation, inhibiting recombinant protein production, etc. Therefore, in this study, to reduce the carbon traffic at pyruvate node and eliminate acetate production, we attempted the down-regulation of glycolytic pathway and disruption of byproducts formation pathway. We also attempted to operate TCA cycle/glyoxylate shunt to reduce the carbon traffic at pyruvate node. The performance of mutant strains were analyzed under different aeration conditions and the efficiency of each approaches in reducing acetate accumulation and improving co-production were addressed.
 Ashok, Somasundar, et al. "Development of recombinant Klebsiella pneumoniae DdhaTstrain for the co-production of 3-hydroxypropionic acid and 1, 3-propanediol from glycerol." Applied microbiology and biotechnology 90.4 (2011): 1253-1265.
 Kumar, Vinod, et al. "Co-production of 3-hydroxypropionic acid and 1, 3-propanediol from glycerol using resting cells of recombinant Klebsiella pneumoniae J2B strain overexpressing aldehyde dehydrogenase." Applied microbiology and biotechnology 96.2 (2012): 373-383.