FIG 8.

Schematic of esculin and salicin utilization in E. coli in the absence of bglB and ascB. In the parent strain, the level of bglA expression is sufficient only for arbutin degradation. In the first-step Esc⁺ mutant, insertion of four nucleotides within the bglA promoter (jagged arrow) results in higher levels of BglA (filled ovals), which are necessary for both esculin and salicin degradation. In the next-step Sal⁺ mutant, a point mutation within the bglA ORF (filled star) results in salicin degradation. The mutant protein is shown as ovals with white stars.