title: Continuous D-lactic acid production by a novel thermotolerant Lactobacillus delbrueckii subsp. lactis QU 41.
abstract: We isolated and characterized a D-lactic acid-producing lactic acid bacterium (D-LAB), identified as Lactobacillus delbrueckii subsp. lactis QU 41. When compared to Lactobacillus coryniformis subsp. torquens JCM 1166 (T) and L. delbrueckii subsp. lactis JCM 1248 (T), which are also known as D-LAB, the QU 41 strain exhibited a high thermotolerance and produced D-lactic acid at temperatures of 50 °C and higher. In order to optimize the culture conditions of the QU 41 strain, we examined the effects of pH control, temperature, neutralizing reagent, and initial glucose concentration on D-lactic acid production in batch cultures. It was found that the optimal production of 20.1 g/l D-lactic acid was acquired with high optical purity (>99.9% of D-lactic acid) in a pH 6.0-controlled batch culture, by adding ammonium hydroxide as a neutralizing reagent, at 43 °C in MRS medium containing 20 g/l glucose. As a result of product inhibition and low cell density, continuous cultures were investigated using a microfiltration membrane module to recycle flow-through cells in order to improve D-lactic acid productivity. At a dilution rate of 0.87 h(-1), the high cell density continuous culture exhibited the highest D-lactic acid productivity of 18.0 g/l/h with a high yield (ca. 1.0 g/g consumed glucose) and a low residual glucose (<0.1 g/l) in comparison with systems published to date.
authors.affiliation: Department of Life Study, Seinan Jo Gakuin University Junior College, Kokura, Kitakyushu, Fukuoka, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Tashiro
authors.forename: Wataru
authors.initials: W
authors.lastname: Kaneko
authors.forename: Yanqi
authors.initials: Y
authors.lastname: Sun
authors.forename: Keisuke
authors.initials: K
authors.lastname: Shibata
authors.forename: Kentaro
authors.initials: K
authors.lastname: Inokuma
authors.forename: Takeshi
authors.initials: T
authors.lastname: Zendo
authors.forename: Kenji
authors.initials: K
authors.lastname: Sonomoto
mesh_terms: D003470:Culture Media / Q000737:chemistry; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D005947:Glucose / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism*; D048668:Lactobacillus delbrueckii / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects*; D008969:Molecular Sequence Data; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D003470:Culture Media; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S; D019344:Lactic Acid; D005947:Glucose