Optimization of TAG production from xylose by R. opacus Xsp8 in batch-culture fermentations. (a) Central composite experimental design matrix defining xylose and (NH4)2SO4 concentrations. X1, xylose concentration (g L-1); X2, (NH4)2SO4 concentration (g L-1). The strain was inoculated in the modified defined medium supplemented with gentamicin in Sixfors-bioreactors. The data for TAG production as fatty acids represent the maximum values during 10 days of cultivation. (b) Response surface plot of the effect of xylose and (NH4)2SO4 concentrations on fatty acid production. Curves and points represent predicted values and experimental data, respectively.