Microbial production of medium‐chain‐length 3‐hydroxyalkanoic acids by recombinant Pseudomonas putida KT2442 harboring genes fadL , fadD and phaZ

Monomers of microbial polyhydroxyalkanoates, mainly 3‐hydroxyhexanoic acid (3HHx) and 3‐hydroxyoctanoic acid (3HO), were produced by overexpressing polyhydroxyalkanoates depolymerase gene phaZ , together with putative long‐chain fatty acid transport protein fadL of Pseudomonas putida KT2442 and acyl‐CoA synthetase ( fadD ) of Escherichia coli MG1655 in P. putida KT2442. FadL Pp , which is responsible for free fatty acid transportation from the extracellular environment to the cytoplasm, and FadD Ec , which activates fatty acid to acyl‐CoA, jointly reinforce the fatty acid β‐oxidation pathway. Pseudomonas putida KT2442 (pYZPst01) harboring polyhydroxyalkanoates depolymerase gene phaZ of Pseudomonas stutzeri 1317 produced 1.37 g L −1 extracellular 3HHx and 3HO in shake flask studies after 48 h in the presence of sodium octanoate as a sole carbon source, while P. putida KT2442 (pYZPst06) harboring phaZ Pst , fadD Ec and fadL Pp achieved 2.32 g L −1 extracellular 3HHx and 3HO monomer production under the same conditions. In a 48‐h fed‐batch fermentation process conducted in a 6‐L fermentor with 3 L sodium octanoate mineral medium, 5.8 g L −1 extracellular 3HHx and 3HO were obtained in the fermentation broth. This is the first time that medium‐chain‐length 3‐hydroxyalkanoic acids (mcl‐3HA) were produced using fadL Pp and fadD Ec genes combined with the polyhydroxyalkanoates depolymerase gene phaZ .