Fig 1.
Co-culture of two specialist strains.
Co-culture is adjustable to achieve simultaneous fermentation of cellobiose and xylose at different substrate concentration ratios, while single recombinant strain is unable to deal with varying substrate compositions.
Fig 2.
Cellobiose fermentation by S. cerevisiae EJ2.
Experimental and model simulated profiles of (A) cell growth, (B) cellobiose consumption and (C) ethanol production at different initial cellobiose concentrations for S. cerevisiae strain EJ2. Lines represent model predictions and symbols represent the means of duplicate experimental results.
Table 1.
Kinetic model parameters of cellobiose and xylose fermentation by S. cerevisiae EJ2 and SR8, respectively.
Fig 3.
Xylose fermentation by S. cerevisiae SR8.
Experimental and model simulated profiles of (A) cell growth, (B) xylose consumption and (C) ethanol production at different initial xylose concentrations using S. cerevisiae strain SR8. Lines represent model predictions and symbols represent the means of duplicate experimental results.
Fig 4.
Co-fermentation of cellobiose and xylose by the co-culture system at different initial sugar concentrations and inoculum sizes using S. cerevisiae strain EJ2 and SR8.
The initial sugar concentrations are 40 g/L cellobiose+40 g/L xylose (A) and 80 g/L cellobiose+40 g/L xylose (B and C). The initial cell densities of EJ2+SR8 were 0.45 g dry cell weight/L+0.45 g dry cell weight/L (A and B) and 0.45 g dry cell weight /L+0.9 g dry cell weight /L (C). Lines represent model predictions and symbols represent experimental data (blue solid line, model curve of cellobiose consumption; blue dash line, model curve of xylose consumption; red solid line, model curve of cell growth; red dash line, model curve of ethanol production; blue solid circle, cellobiose concentration (g/L); blue hallow circle, xylose concentration (g/L); red solid circle, cell density (g dry cell weight /L); red hallow circle, ethanol concentration (g/L)).Experimental results are the means of duplicate experiments; error bars indicating standard deviations are not visible when smaller than the symbol size.
Fig 5.
Validation of co-culture model prediction for simultaneous fermentation of cellobiose and xylose by S. cerevisiae strains EJ2 and SR8.
The initial sugar concentrations are 60 g/L cellobiose+20 g/L xylose. The initial cell densities of EJ2+SR8 were 0.45 g dry cell weight /L+0.9 g dry cell weight /L. (blue solid line, model curve of cellobiose consumption; blue dash line, model curve of xylose consumption; red solid line, model curve of cell growth; red dash line, model curve of ethanol production; blue solid circle, cellobiose concentration (g/L); blue hallow circle, xylose concentration (g/L); red solid circle, cell density (g dry cell weight /L); red hallow circle, ethanol concentration (g/L)).Experimental results are the means of duplicate experiments; error bars indicating standard deviations are not visible when smaller than the symbol size.
Table 2.
Values of weighing factors of in the model for cellobiose and xylose co-fermentation by the co-culture of S. cerevisiae EJ2 and SR8.