title: Metabolic engineering of a reduced-genome strain of Escherichia coli for L-threonine production.
abstract: BACKGROUND
  Deletion of large blocks of nonessential genes that are not needed for metabolic pathways of interest can reduce the production of unwanted by-products, increase genome stability, and streamline metabolism without physiological compromise. Researchers have recently constructed a reduced-genome Escherichia coli strain MDS42 that lacks 14.3% of its chromosome.
  
  
  RESULTS
  Here we describe the reengineering of the MDS42 genome to increase the production of the essential amino acid L-threonine. To this end, we over-expressed a feedback-resistant threonine operon (thrA*BC), deleted the genes that encode threonine dehydrogenase (tdh) and threonine transporters (tdcC and sstT), and introduced a mutant threonine exporter (rhtA23) in MDS42. The resulting strain, MDS-205, shows an ~83% increase in L-threonine production when cells are grown by flask fermentation, compared to a wild-type E. coli strain MG1655 engineered with the same threonine-specific modifications described above. And transcriptional analysis revealed the effect of the deletion of non-essential genes on the central metabolism and threonine pathways in MDS-205.
  
  
  CONCLUSIONS
  This result demonstrates that the elimination of genes unnecessary for cell growth can increase the productivity of an industrial strain, most likely by reducing the metabolic burden and improving the metabolic efficiency of cells.
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea. sunkim@kaist.ac.kr.
authors.forename: Jun Hyoung
authors.initials: JH
authors.lastname: Lee
authors.forename: Bong Hyun
authors.initials: BH
authors.lastname: Sung
authors.forename: Mi Sun
authors.initials: MS
authors.lastname: Kim
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Blattner
authors.forename: Byoung Hoon
authors.initials: BH
authors.lastname: Yoon
authors.forename: Jung Hoe
authors.initials: JH
authors.lastname: Kim
authors.forename: Sun Chang
authors.initials: SC
authors.lastname: Kim