Sporulation and respiratory metabolism in the "petite negative" yeast Hansenula saturnuss

Upon transition from growth medium to acetate sporulation medium buffered at pH 6.1 with 0.2 M PIPES, Hansenula saturnus showed a respiratory activity which was 88% antimycin A sensitive (1st) and 12% high azide sensitive (3rd), as in acetate complete growth medium. After ≅ 10 h, 3rd respiration declined and oxygen consumption was inhibited by the simultaneous addition of antimycin A and hydroxamate, a situation which lasted until the appearance of the first asci. Later on, 1st and 3rd respiration reappeared and asci formation was completed under these respiratory conditions. The growth in the presence of antimycin A or erythromycin affected only quantitatively the ascospore production and this is because in sporulation medium there was a de novo synthesis of the mitochondrial components of the respiratory chain. Cells which were avoid of 1st respiration but possessed 2nd or 3rd respiration could sporulate, indicating that these alternative respirations also have a role in the process. This was confirmed by the inhibition of sporulation as occurred in the presence of inhibitors of 1st, 2nd and 3rd respiration in sporulation medium.