FIG. 4.

Influence of hydrogen peroxide on the growth of L. delbrueckii subsp. bulgaricus under nonaerated conditions. MRS medium with 2% lactose was used. Growth was measured through changes in A₆₀₀. (A) Influence of hydrogen peroxide concentration. Hydrogen peroxide was added at the time indicated by the arrow to reach final concentrations of 0 (○), 0.5 (□), 1 (▵), and 5 (◊) mM. (B) Influence of the time of addition. Hydrogen peroxide was added at different times to give the same final concentration of 0.75 mM in parallel unaerated cultures. H₂O₂ was added immediately after inoculation (X), when A₆₀₀ = 0.150 (□), when A₆₀₀ = 0.350 (▵), when A₆₀₀ = 0.600 (+), and when A₆₀₀ = 1 (◊). ○, growth without addition of hydrogen peroxide.