Abstract
The effects of chloramphenicol (CAP) on mitochondrial respiratory activity in the wild strain (ST) and in a cytoplasmic CAP-resistant mutant (STR1) of Tetrahymena pyriformis were studied by determining oxygen consumption, by spectrophotometry, and by cytochemistry. In the absence of CAP both strains had the same respiration capacity, and the low-temperature spectra of their isolated mitochondria were similar. Furthermore, the mitochondria of both strains showed a positive reaction with diaminobenzidine, denoting a similar cytochrome oxidase activity. However, when cells were grown in CAP for 24 or 48 h, the peaks of cytochrome oxidase and cytochromb b were almost absent in the wild type. In this type the oxygen consumption was greatly decreased, and the mitochondria were no longer stained by diaminobenzidine. In the mutant, the peaks of cytochrome oxidase and cytochrome b were decreased only; respiration was less affected than in the wild type, and cytochrome oxidase activity was still disclosed by the diaminobenzidine reaction. These results show that CAP inhibits the synthesis of two cytochromes (b and oxidase) which are partially translated into the mitochrondria of T. pyriformis. In the mutant, CAP reduces only the mitochondrial translation, resulting in reduced mitochondrial activity and reduced growth rate of the cell. These results are compared with the nucleo-mitochondrial regulation mechanisms discussed in our previous works.