title: Metabolic engineering and flux analysis of Corynebacterium glutamicum for L-serine production.
abstract: L-Serine plays a critical role as a building block for cell growth, and thus it is difficult to achieve the direct fermentation of L-serine from glucose. In this study, Corynebacterium glutamicum ATCC 13032 was engineered de novo by blocking and attenuating the conversion of L-serine to pyruvate and glycine, releasing the feedback inhibition by L-serine to 3-phosphoglycerate dehydrogenase (PGDH), in combination with the co-expression of 3-phosphoglycerate kinase (PGK) and feedback-resistant PGDH (PGDH(r)). The resulting strain, SER-8, exhibited a lower specific growth rate and significant differences in L-serine levels from Phase I to Phase V as determined for fed-batch fermentation. The intracellular L-serine pool reached (14.22 ± 1.41) μmol g(CDM) (-1), which was higher than glycine pool, contrary to fermentation with the wild-type strain. Furthermore, metabolic flux analysis demonstrated that the over-expression of PGK directed the flux of the pentose phosphate pathway (PPP) towards the glycolysis pathway (EMP), and the expression of PGDH(r) improved the L-serine biosynthesis pathway. In addition, the flux from L-serine to glycine dropped by 24%, indicating that the deletion of the activator GlyR resulted in down-regulation of serine hydroxymethyltransferase (SHMT) expression. Taken together, our findings imply that L-serine pool management is fundamental for sustaining the viability of C. glutamicum, and improvement of C(1) units generation by introducing the glycine cleavage system (GCV) to degrade the excessive glycine is a promising target for L-serine production in C. glutamicum.
authors.affiliation: Department of Industrial Microbiology and Biotechnology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Shujuan
authors.initials: S
authors.lastname: Lai
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhang
authors.forename: Shuwen
authors.initials: S
authors.lastname: Liu
authors.forename: Yong
authors.initials: Y
authors.lastname: Liang
authors.forename: Xiuling
authors.initials: X
authors.lastname: Shang
authors.forename: Xin
authors.initials: X
authors.lastname: Chai
authors.forename: Tingyi
authors.initials: T
authors.lastname: Wen
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D019149:Bioreactors / Q000382:microbiology; D048230:Corynebacterium glutamicum / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D005285:Fermentation; D015964:Gene Expression Regulation, Bacterial; D005947:Glucose / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D012696:Glycine Hydroxymethyltransferase / Q000235:genetics / Q000378:metabolism; D006019:Glycolysis / Q000235:genetics; D060847:Metabolic Engineering / Q000379:methods*; D010427:Pentose Phosphate Pathway / Q000235:genetics; D050543:Phosphoglycerate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D010735:Phosphoglycerate Kinase / Q000235:genetics / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D012694:Serine / Q000096:biosynthesis*
chemical_list: D001426:Bacterial Proteins; D012694:Serine; D019289:Pyruvic Acid; D050543:Phosphoglycerate Dehydrogenase; D012696:Glycine Hydroxymethyltransferase; D010735:Phosphoglycerate Kinase; D005947:Glucose; D005998:Glycine