title: Improved homo L-lactic acid fermentation from xylose by abolishment of the phosphoketolase pathway and enhancement of the pentose phosphate pathway in genetically modified xylose-assimilating Lactococcus lactis.
abstract: In order to achieve efficient homo L-lactic acid fermentation from xylose, we first carried out addition of xylose assimilation ability to Lactococcus lactis IL 1403 by introducing a plasmid carrying the xylRAB genes from L. lactis IO-1 (pXylRAB). Then modification of xylose assimilation pathway was carried out. L. lactis has two pathways for xylose assimilation called the phosphoketolase pathway (PK pathway) that produces both lactic acid and acetic acid and the pentose phosphate pathway (PP pathway) that produces only lactic acid as a final product. Thus a mutant strain that disrupted its phosphokeolase gene (ptk) was constructed. The Δptk mutant harboring pXylRAB lacked the PK pathway and produced predominantly lactic acid from xylose via the PP pathway, although its fermentation rate slightly decreased. Further introduction of the transketolase gene (tkt) to disrupted ptk locus led restoration of fermentation rate and this was attributed to enhancement of the PP pathway. As a result, ptk::tkt strain harboring pXylRAB produced 50.1 g/l of L-lactic acid from xylose with a high optical purity of 99.6% and a high yield of 1.58 (moles per mole xylose consumed) that is close to theoretical value of 1.67 from xylose.
authors.affiliation: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodaicho, Nada-ku, Kobe, 657-8501, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Shinkawa
authors.forename: Kenji
authors.initials: K
authors.lastname: Okano
authors.forename: Shogo
authors.initials: S
authors.lastname: Yoshida
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Tanaka
authors.forename: Chiaki
authors.initials: C
authors.lastname: Ogino
authors.forename: Hideki
authors.initials: H
authors.lastname: Fukuda
authors.forename: Akihiko
authors.initials: A
authors.lastname: Kondo
mesh_terms: D000446:Aldehyde-Lyases / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D005285:Fermentation; D005818:Genetic Engineering; D019344:Lactic Acid / Q000378:metabolism*; D013294:Lactococcus lactis / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010427:Pentose Phosphate Pathway; D014174:Transketolase / Q000235:genetics / Q000378:metabolism; D014994:Xylose / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D019344:Lactic Acid; D014994:Xylose; D014174:Transketolase; D000446:Aldehyde-Lyases; C022367:phosphoketolase