Lactic acid production from xylose by engineered Saccharomyces cerevisiae without PDC or ADH deletion

Lactic acid is mainly used to produce bio-based, bio-degradable polylactic acid. For industrial production of lactic acid, engineered Saccharomyces cerevisiae can be used. To avoid cellular toxicity caused by lactic acid accumulation, pH-neutralizing agents are used, leading to increased production costs. In this study, lactic acid-producing S. cerevisiae BK01 was developed with improved lactic acid tolerance through adaptive laboratory evolution (ALE) on 8% lactic acid. The genetic basis of BK01 could not be determined, suggesting complex mechanisms associated with lactic acid tolerance. However, BK01 had distinctive metabolomic traits clearly separated from the parental strain, and lactic acid production was improved by 17% (from 102 g/L to 119 g/L). To the best of our knowledge, this is the highest lactic acid titer produced by engineered S. cerevisiae without the use of pH neutralizers. Moreover, cellulosic lactic acid production by BK01 was demonstrated using acetate-rich buckwheat husk hydrolysates. Particularly, BK01 revealed improved tolerance against acetic acid of the hydrolysates, a major fermentation inhibitor of lignocellulosic biomass. In short, ALE with a high concentration of lactic acid improved lactic acid production as well as acetic acid tolerance of BK01, suggesting a potential for economically viable cellulosic lactic acid production.

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Lactic Acid Production from a Whole Slurry of Acid-Pretreated Spent Coffee Grounds by Engineered Saccharomyces cerevisiae

Applied Biochemistry and Biotechnology ◽

10.1007/s12010-019-03000-6 ◽

2019 ◽

Vol 189 (1) ◽

pp. 206-216 ◽

Cited By ~ 3

Author(s):

Jeong-won Kim ◽

Jeong Hwa Jang ◽

Hyeon Jin Yeo ◽

Jeongman Seol ◽

Soo Rin Kim ◽

...

Keyword(s):

Saccharomyces Cerevisiae ◽

Lactic Acid ◽

Acid Production ◽

Lactic Acid Production ◽

Spent Coffee Grounds ◽

Coffee Grounds ◽

Engineered Saccharomyces Cerevisiae ◽

Whole Slurry

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Improvement of Lactic Acid Production in Saccharomyces cerevisiae by Cell Sorting for High Intracellular pH

Applied and Environmental Microbiology ◽

10.1128/aem.00683-06 ◽

2006 ◽

Vol 72 (8) ◽

pp. 5492-5499 ◽

Cited By ~ 82

Author(s):

Minoska Valli ◽

Michael Sauer ◽

Paola Branduardi ◽

Nicole Borth ◽

Danilo Porro ◽

...

Keyword(s):

Saccharomyces Cerevisiae ◽

Lactic Acid ◽

Intracellular Ph ◽

Cell Sorting ◽

Acid Production ◽

Lactic Acid Production ◽

Low Ph ◽

The Mean ◽

High Level ◽

Lactate Dehydrogenases

ABSTRACT Yeast strains expressing heterologous l-lactate dehydrogenases can produce lactic acid. Although these microorganisms are tolerant of acidic environments, it is known that at low pH, lactic acid exerts a high level of stress on the cells. In the present study we analyzed intracellular pH (pHi) and viability by staining with cSNARF-4F and ethidium bromide, respectively, of two lactic-acid-producing strains of Saccharomyces cerevisiae, CEN.PK m850 and CEN.PK RWB876. The results showed that the strain producing more lactic acid, CEN.PK m850, has a higher pHi. During batch culture, we observed in both strains a reduction of the mean pHi and the appearance of a subpopulation of cells with low pHi. Simultaneous analysis of pHi and viability proved that the cells with low pHi were dead. Based on the observation that the better lactic-acid-producing strain had a higher pHi and that the cells with low pHi were dead, we hypothesized that we might find better lactic acid producers by screening for cells within the highest pHi range. The screening was performed on UV-mutagenized populations through three consecutive rounds of cell sorting in which only the viable cells within the highest pHi range were selected. The results showed that lactic acid production was significantly improved in the majority of the mutants obtained compared to the parental strains. The best lactic-acid-producing strain was identified within the screening of CEN.PK m850 mutants.

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