(R)-3HB-CoA is hydrolyzed into (R)-3HB by modifying enzymes or undergoes 2 degradation of the polymerized product. In the present study, we constructed a new (R)-3HB-generating pathway from glucose by using propionyl-CoA transferase (PCT).This pathway was designed to excrete (R)-3HB by means of a PCT-catalyzed reaction coupled with regeneration of acetyl-CoA, the starting substance for synthesizing (R)-3HB-CoA. Considering the equilibrium reaction of PCT, the PCT-catalyzed (R)-3HB production would be expected to be facilitated by the addition of acetate since it acts as an acceptor of CoA. As expected, the engineered Escherichia coli harboring the phaAB and pct genes produced 1.0 g L -1 (R)-3HB from glucose, and with the addition of acetate into the medium, the concentration was increased up to 5.2 g L -1 , with a productivity of 0.22 g L -1 h -1 . The effectiveness of the extracellularly added acetate was evaluated by monitoring the conversion of 13 C carbonyl carbon labeled acetate into (R)-3HB using gas chromatography/mass spectrometry. The enantiopurity of (R)-3HB was determined to be 99.2% using chiral liquid chromatography. These results demonstrate that the PCT pathway achieved a rapid co-conversion of glucose and acetate into (R)-3HB.

We regret that the gene source of propionyl-CoA transferase was wrongly given as Clostridium propionicum whereas it should have been Megasphaera elsdenii, and that the accession number of the gene product was wrongly given as AJ276553 whereas it should have been YP_004765791. The publishers apologise for this errorThe online version of the original article can be found at http://dx