title: Improvement of 1,3-propanediol production using an engineered cyanobacterium, Synechococcus elongatus by optimization of the gene expression level of a synthetic metabolic pathway and production conditions.
abstract: The introduction of a synthetic metabolic pathway consisting of multiple genes derived from various organisms enables cyanobacteria to directly produce valuable chemicals from carbon dioxide. We previously constructed a synthetic metabolic pathway composed of genes from Escherichia coli, Saccharomyces cerevisiae, and Klebsiella pneumoniae. This pathway enabled 1,3-propanediol (1,3-PDO) production from cellular DHAP via glycerol in the cyanobacterium, Synechococcus elongatus PCC 7942. The production of 1,3-PDO (3.79mM, 0.29g/l) directly from carbon dioxide by engineered S. elongatus PCC 7942 was successfully accomplished. However, the constructed strain accumulated a remarkable amount of glycerol (12.6mM, 1.16g/l), an intermediate metabolite in 1,3-PDO production. Notably, enhancement of latter reactions of synthetic metabolic pathway for conversion of glycerol to 1,3-PDO increases 1,3-PDO production. In this study, we aimed to increase the observed 1,3-PDO production titer. First, the weaker S. elongatus PCC 7942 promoter, PLlacO1, was replaced with a stronger promoter (Ptrc) to regulate genes involved in the conversion of glycerol to 1,3-PDO. Second, the induction timing for gene expression and medium composition were optimized. Promoter replacement resulted in higher 1,3-PDO production than glycerol accumulation, and the amount of products (1,3-PDO and glycerol) generated via the synthetic metabolic pathway increased with optimization of medium composition. Accordingly, we achieved the highest titer of 1,3-PDO (16.1mM, 1.22g/l) and this was higher than glycerol accumulation (9.46mM, 0.87g/l). The improved titer was over 4-fold higher than that of our previous study.
authors.affiliation: Laboratory for Bioinformatics, Graduate School of Systems Biosciences, Kyushu University, 804 Westwing, Westwing, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Hirokawa
authors.affiliation: Laboratory for Bioinformatics, Graduate School of Systems Biosciences, Kyushu University, 804 Westwing, Westwing, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Maki
authors.affiliation: Laboratory for Bioinformatics, Graduate School of Systems Biosciences, Kyushu University, 804 Westwing, Westwing, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Electronic address: taizo@brs.kyushu-u.ac.jp.
authors.forename: Taizo
authors.initials: T
authors.lastname: Hanai
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D019149:Bioreactors / Q000382:microbiology*; D053898:Biosynthetic Pathways / Q000502:physiology*; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D024861:Genetic Enhancement / Q000379:methods*; D005990:Glycerol / Q000378:metabolism*; D060847:Metabolic Engineering / Q000379:methods; D053858:Metabolic Networks and Pathways / Q000502:physiology; D011409:Propylene Glycols / Q000302:isolation & purification / Q000378:metabolism*; D013045:Species Specificity; D046940:Synechococcus / Q000145:classification / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D011409:Propylene Glycols; C041787:1,3-propanediol; D005990:Glycerol
keywords: 1,3-propanediol (PDO); Cyanobacteria; Synthetic metabolic pathway