Production of Lactate by Metabolically Engineered Scheffersomyces stipitis

Area of Science:

• Biotechnology
• Industrial Microbiology
• Metabolic Engineering

Background:

• Lactate is a valuable industrial chemical.
• Scheffersomyces stipitis is a yeast capable of fermenting hexoses and pentoses, making it a promising host for lignocellulosic biomass conversion.
• S. stipitis does not naturally produce lactate, necessitating genetic engineering for its production.

Purpose of the Study:

• To engineer Scheffersomyces stipitis for the production of L-lactate.
• To evaluate the efficiency of engineered S. stipitis in producing lactate from lignocellulosic sugars (glucose and xylose).

Main Methods:

• Engineered S. stipitis by expressing two codon-optimized bacterial L-lactate dehydrogenase genes.
• Utilized strong native promoters to drive gene expression.
• Optimized fermentation conditions, including temperature and pH control.

Main Results:

• Achieved lactate titers of 7.42 g/L (0.46 g/g yield) from glucose and 11.67 g/L (0.58 g/g yield) from xylose.
• Reached a maximum titer of 19.27 g/L (0.52 g/g yield) from 50 g/L xylose after 74 hours.
• Optimized fermentation temperature (32 °C) and neutralizing agent improved yield by 30% and 25%, respectively.
• Engineered strain produced ethanol only on glucose, not on xylose, unlike the wildtype.

Conclusions:

• Engineered S. stipitis is a viable host for microbial lactate production from lignocellulosic sugars.
• Optimized fermentation conditions significantly enhance lactate yield and productivity.
• The selective production of lactate over ethanol on xylose presents a biotechnological advantage.