title: Production of D-lactic acid in a continuous membrane integrated fermentation reactor by genetically modified Saccharomyces cerevisiae: enhancement in D-lactic acid carbon yield.
abstract: Poly d-lactic acid is an important polymer because it improves the thermostability of poly l-lactic acid by stereo complex formation. To demonstrate potency of continuous fermentation using a membrane-integrated fermentation reactor (MFR) system, continuous fermentation using genetically modified Saccharomyces cerevisiae which produces d-lactic acid was performed at the low pH and microaerobic conditions. d-Lactic acid continuous fermentation using the MFR system by genetically modified yeast increased production rate by 11-fold compared with batch fermentation. In addition, the carbon yield of d-lactic acid in continuous fermentation was improved to 74.6 ± 2.3% compared to 39.0 ± 1.7% with batch fermentation. This dramatic improvement in carbon yield could not be explained by a reduction in carbon consumption to form cells compared to batch fermentation. Further detailed analysis at batch fermentation revealed that the carbon yield increased to 76.8% at late stationary phase. S. cerevisiae, which exhibits the Crabtree-positive effect, demonstrated significant changes in metabolic activities at low sugar concentrations (Rossignol et al., Yeast, 20, 1369-1385, 2003). Moreover, lactate-producing S. cerevisiae requires ATP supplied not only from the glycolytic pathway but also from the TCA cycle (van Maris et al., Appl. Environ. Microbiol., 70, 2898-2905, 2004). Our finding was revealed that continuous fermentation, which can maintain the conditions of both a low sugar concentration and air supply, results in Crabtree-positive and lactate-producing S. cerevisiae for suitable conditions of d-lactic acid production with respect to redox balance and ATP generation because of releasing the yeast from the Crabtree effect.
authors.affiliation: New Frontiers Research Laboratories, Toray Industries, Inc., 6-10-1 Tebiro, Kamakura, Kanagawa 248-8555, Japan. Electronic address: Takashi_Mimitsuka@nts.toray.co.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Mimitsuka
authors.affiliation: New Frontiers Research Laboratories, Toray Industries, Inc., 6-10-1 Tebiro, Kamakura, Kanagawa 248-8555, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Sawai
authors.affiliation: New Frontiers Research Laboratories, Toray Industries, Inc., 6-10-1 Tebiro, Kamakura, Kanagawa 248-8555, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Kobayashi
authors.affiliation: New Frontiers Research Laboratories, Toray Industries, Inc., 6-10-1 Tebiro, Kamakura, Kanagawa 248-8555, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tsukada
authors.affiliation: Global Environment Research Laboratories, Toray Industries, Inc., 1-1-1 Sonoyama, Ohtsu, Shiga 520-8558, Japan.
authors.forename: Norihiro
authors.initials: N
authors.lastname: Takeuchi
authors.affiliation: New Frontiers Research Laboratories, Toray Industries, Inc., 6-10-1 Tebiro, Kamakura, Kanagawa 248-8555, Japan.
authors.forename: Katsushige
authors.initials: K
authors.lastname: Yamada
authors.affiliation: Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan.
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Ogino
authors.affiliation: New Frontiers Research Laboratories, Toray Industries, Inc., 6-10-1 Tebiro, Kamakura, Kanagawa 248-8555, Japan.
authors.forename: Tetsu
authors.initials: T
authors.lastname: Yonehara
mesh_terms: D061249:Batch Cell Culture Techniques; D019149:Bioreactors; D002244:Carbon / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005285:Fermentation; D007773:Lactates / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism; D008567:Membranes, Artificial; D010084:Oxidation-Reduction; D011091:Polyesters; D011108:Polymers / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*
chemical_list: D007773:Lactates; D008567:Membranes, Artificial; D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide); D002244:Carbon
keywords: Continuous fermentation; Crabtree effect; Lactic acid; Membrane bioreactor; Saccharomyces cerevisiae