Light-induced tetracycline accumulation by Rhodopseudomonas sphaeroides

Light has been used as a primary energy source in studies of tetracycline transport by Rhodopseudomonas sphaeroides. Accumulation of the antibiotic occurs in light, while efflux occurs in dark. Both fluorescence enhancement and radioisotopic tracing have been used to monitor transport. Km's obtained from both techniques are similar. Light-induced accumulation of tetracyclines is inhibited by a variety of inhibitors, including antimycin A, N-ethylmaleimide, carbonylcyanide m-chlorophenylhydrazone, and 2,4-dinitrophenol. A rapid efflux is observed after loading when cells are placed in the dark or treated with inhibitors.