The requirement of oxygen for incorporation of carbon from D-xylose and D-glucose by Pachysolen tannophilus.

Oxygen was required for growth of Pachysolen tannophilus on D-xylose, as well as on D-glucose. The reason was not identical to that of other yeasts whose anaerobic growth is stimulated by supplementation of the medium with lipids or organic hydrogen acceptors, as such supplements were ineffective with P. tannophilus. The requirement of oxygen was found to be due to its involvement in the incorporation of carbon from D-xylose, and to a large extent D-glucose as well, into trichloracetic acid-insoluble material. The role it played was associated with the channeling of catabolic intermediates into biosynthetic routes, since ethanol was formed anaerobically, but aeration was required for induction of several enzymes associated with the catabolism of D-xylose. The requirement suggested that normally functioning mitochondria were necessary for incorporation and growth, but not ethanol formation. This view was supported by the inability to obtain stable petite mutants, and by the effects of inhibitors of mitochondrial function, which caused effects on incorporation and growth under aerobic conditions similar to those of anaerobiosis.