Abstract
Production of the biopolymer polyhydroxybutyrate (PHB) in Saccharomyces cerevisiae starts at the end of exponential phase particularly when the specific growth rate is decreased due to the depletion of glucose in the medium. The specific growth rate and the type of carbon source (fermentable/non-fermentable) have been known to influence the cell physiology and hence affect the fermentability of S. cerevisiae. The production of PHB utilizes cytosolic acetyl-CoA as a precursor and the S. cerevisiae employed in this study is therefore a strain with the enhanced cytosolic acetyl-CoA supply. Growth and PHB production at different specific growth rates were evaluated on glucose, ethanol and a mixture of glucose and ethanol as carbon source. Ethanol as carbon source yielded a higher PHB production compared to glucose since it can be directly used for cytosolic acetyl-CoA production and hence serves as a precursor for PHB production. However, this carbon source results in lower biomass yield and hence it was found that to ensure both biomass formation and PHB production a mixture of glucose and ethanol was optimal, and this resulted in the highest volumetric productivity of PHB, 8.23 mg/L · h-1, at a dilution rate of 0.1 h-1.
Highlights
IntroductionThe well-established knowledge and the availability of genome data have led to its versatile use as a cell factory for many industrial products (Ostergaard et al 2000)
Saccharomyces cerevisiae is a biotechnologically important microorganism
In this study, when the chemostat was operated at dilution rates of 0.15 h-1 and 0.2 h-1, ethanol was produced in the medium as an evidence of a respiro-fermentative metabolism of S. cerevisiae, which can ferment glucose at a high dilution rate (Duntze et al 1969; Hanegraaf et al 2000; Maaheimo et al 2001)
Summary
The well-established knowledge and the availability of genome data have led to its versatile use as a cell factory for many industrial products (Ostergaard et al 2000). Process optimization for production of various industrial products such as biofuels, fine and bulk chemicals in S. cerevisiae has been studied by several research groups (de Jong et al 2012; Hong and Nielsen 2012; Nevoigt 2008; Ostergaard et al 2000; Steen et al 2008) This reveals the physiological adaptability of S. cerevisiae to a highly variable environment. According to a respiratory-fermentative metabolism in S. cerevisiae, the type (fermentable/non fermentable) and concentration of carbon source as well as the availability of oxygen are important factors driving the metabolic pattern in the yeast.
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