The effects of oxygen availability on the rate of growth and on RNA and protein metabolism in Rhodotorula gracilis

The present work deals with the effects of low oxygen availability on the rate of growth and of RNA and protein synthesis in Rhodotorula gracilis cells growing in a liquid mineralglucose medium. In these experiments O2 partial pressure in tl.!e medium has been measured and maintained satisfactorily constant by means of a Clark oxygen electrode. It has been found that: a) the optimal rate of growth requires O2 partial pressure above 3 mm of Hg; b) lowering O2 pressure below this value induces a progressive inhibition of growth; c) under conditions of suboptimal O2 availability (ca. 1 ±0.2 mm Hg) the accumulation of RNA and DNA is inhibited in an earlier period and to larger extent than protein synthesis. Experiments of incorporation of 32p orthophosphate into RNA show that the « low O2 » condition is characterized by a marked inhibition of RNA synthesis, even in the case of relatively short 'pulses' (5 minutes), while no important changes of the rate RNA breakdown is observed. In fact, the rate of 32p incorporation into RNA remains practically linear in time for at least 30 minutes. This behaviour is in contrast with the one observed in this yeast as a consequence of nitrogen or of glucose starvation; in these cases the block of the net synthesis of RNA appears to correspond rather to an increased rate of breakdown of the newly formed RNA than to an inhibition at transcription level.