Metabolic engineering of a reduced-genome strain of Escherichia coli for L-threonine production.
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.
Lee
Jun Hyoung
JH
Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea. sunkim@kaist.ac.kr.
Sung
Bong Hyun
BH
Kim
Mi Sun
MS
Blattner
Frederick R
FR
Yoon
Byoung Hoon
BH
Kim
Jung Hoe
JH
Kim
Sun Chang
SC