Correlation between cytochrome aa3 concentrations and streptomycin accumulation in Bacillus subtilis

Accumulation of aminoglycosides by Bacillus subtilis appears to require specific components of the electron transport chain. These components include cytochromes and the lipophilic quinone vitamin K2. The present study concerns the importance of cytochrome aa3, a terminal oxidase, in the uptake of streptomycin. Growth conditions have been established such that the concentration of cytochrome aa3 can be modified over a wide range; on defined minimal salts agar, the wild-type strain (RB1) and an strC mutant (RB95) synthesized cytochrome aa3 only when adequate amounts of Casamino Acids (Difco Laboratories, Detroit, Mich.) were present. A positive correlation between cytochrome aa3 levels and streptomycin accumulation was observed. The same correlation was seen when cytochrome aa3 was measured in relation to growth susceptibility. These correlations suggest that cytochrome aa3 is necessary for accumulation of streptomycin by B. subtilis.