Figure 2.

Effect of l-alanine and l-Ala-L-Ala on the growth of the wild-type strain and its alaE-deficient derivative. A fully grown cell suspension was serially diluted 10-fold and 5-μL aliquots were spotted onto minimal medium supplemented with 0.5–4.0 mmol/L l-Ala-l-Ala (left panel) or 2.5–20 mmol/L l-Ala (right panel). The top-left panel represents control medium without supplement. Plates were incubated at 37°C for 40 h. Strains used: MG1655, alaE-positive parent strain; MG1655ΔalaE, alaE-deficient isogenic derivative.