Kyungmoon Park

Medium optimization for recombinant protein production by Bacillus subtilis

SummaryOptimal concentrations of glucose, yeast extract and nutrient broth for the production of β-lactamase by B. subtilis were predicted using a statistical experimental design and then tested. More yeast extract (13 vs. 1 g/L), less glucose (7.4 vs. 10 g/L), and less nutrient broth (12.6 vs. 15 g/L) were required to achieve high β-lactamase activities (5700 U/L) instead of high cell growth rates (1.2 h-1).

Enhancement of β-glucosidase stability and cellobiose-usage using surface-engineered recombinant Saccharomyces cerevisiae in ethanol production

To enhance the use of cellobiose by a recombinant Sachharomyces cerevisiae, the expressed β-glucosidase that hydrolyzes cellobiose was stabilized using a surface-display system. The C-terminal half of α-agglutinin was used as surface-display motif for the expression of β-glucosidase in the cell wall. The surface-displayed β-glucosidase had a half-life time (t1/2) of 100 h in acidic culture broth conditions, while secreted β-glucosidase had a t1/2 of 60 h. With such stabilization of β-glucosidase, the surface-engineered S. cerevisiae utilized 7.5 g cellobiose l−1 over 60 h, while S. cerevisiae secreting β-glucosidase into culture broth used 5.8 g cellobiose l−1 over the same period.

L-Glycine Alleviates Furfural-Induced Growth Inhibition during Isobutanol Production in Escherichia coli

Lignocellulose is now a promising raw material for biofuel production. However, the lignin complex and crystalline cellulose require pretreatment steps for breakdown of the crystalline structure of cellulose for the generation of fermentable sugars. Moreover, several fermentation inhibitors are generated with sugar compounds, majorly furfural. The mitigation of these inhibitors is required for the further fermentation steps to proceed. Amino acids were investigated on furfural-induced growth inhibition in E. coli producing isobutanol. Glycine and serine were the most effective compounds against furfural. In minimal media, glycine conferred tolerance against furfural. From the IC₅₀ value for inhibitors in the production media, only glycine could alleviate growth arrest for furfural, where 6 mM glycine addition led to a slight increase in growth rate and isobutanol production from 2.6 to 2.8 g/l under furfural stress. Overexpression of glycine pathway genes did not lead to alleviation. However, addition of glycine to engineered strains blocked the growth arrest and increased the isobutanol production about 2.3-fold.