title: Enhancement of pyruvate productivity in Torulopsis glabrata: Increase of NAD+ availability.
abstract: This study aimed at increasing the pyruvate productivity from a multi-vitamin auxotrophic yeast Torulopsis glabrata, by increasing the availability of NAD+. We examined two strategies for increasing availability of NAD+. To supplement nicotinic acid (NA), the precursor of NAD+; and to increase the activity of alcohol dehydrogenase integrating with addition acetaldehyde as exterior electron acceptor. The addition of 8 mg l(-1) NA to the fermentation medium resulted in a significant increase in the glucose consumption rate (48.4%) and the pyruvate concentration (29%). An ethanol-utilizing mutant WSH-13 was screened and selected after nitrosoguanidine mutagenesis of the parent strain T. glabrata CCTCC M202019. Compared with the parent strain, the alcohol dehydrogenase activity of the mutant WSH-13 increased about 110% and the mutant could utilize ethanol as the sole carbon source for growth (1.8 g l(-1) dry cell weight). When growing with glucose, the addition of 4 mg l(-1) acetaldehyde to the mutant WSH-13 culture broth led to a significant increase in the glucose consumption rate (26.3%) and pyruvate production (22.5%), but the ratio of NADH/NAD+ decreased to 0.22. Acetaldehyde did not affect the glucose and energy metabolism at high dissolved oxygen (DO) concentration. However, at lower DO concentration (20%), maintaining the acetaldehyde concentration in the mutant culture broth at 4 mg l(-1) caused an increased NAD+ concentration but a decreased NADH concentration. As a consequence, the pyruvate production rate, the pyruvate yield on glucose and the pyruvate concentration were 68, 44 and 45% higher, respectively, than the corresponding values of the control (without acetaldehyde). The strategy for increasing the glycolytic flux and the pyruvate productivity in T. glabrata by increasing the availability of NAD+ may provide an alternative approach to enhance the metabolites productivity in yeast.
authors.affiliation: The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Southern Yangtze University, 170 Huihe Road, Wuxi 214036, PR China.
authors.forename: Liming
authors.initials: L
authors.lastname: Liu
authors.forename: Yin
authors.initials: Y
authors.lastname: Li
authors.forename: Zhongping
authors.initials: Z
authors.lastname: Shi
authors.forename: Guocheng
authors.initials: G
authors.lastname: Du
authors.forename: Jian
authors.initials: J
authors.lastname: Chen
mesh_terms: D001682:Biological Availability; D041221:Candida glabrata / Q000235:genetics / Q000378:metabolism*; D018929:Cell Culture Techniques / Q000379:methods*; D024861:Genetic Enhancement / Q000379:methods*; D009243:NAD / Q000378:metabolism*; D019289:Pyruvic Acid / Q000378:metabolism*
chemical_list: D009243:NAD; D019289:Pyruvic Acid