Fig 2.

Identification of critical mutations by site-directed mutation. The aerobic cell growth rates (μ) of strains expressing the third-round mutant with a single back mutation and the wild type with a point (site) mutation were compared to that of the strain expressing the third-round mutant xylose isomerase (μ°). The back mutations at amino acid positions 15 and 142 resulted in 46% and 32% decreases in the growth rates. Combining these two positions improved the performance of wild-type xylose isomerase in aerobic growth on xylose. The error bars represent the standard deviations of biological triplicates.