Methanol metabolism in mutants of the methylotrophic yeast Hansenula polymorpha

Abstract

Three types of Hansenula polymorpha 356 (leu−) mutants unable to grow on methanol were isolated and characterized. The first type of mutants, M8, M14, and M41, were deficient in the alcohol oxidase activity (MOX−). The dihydroxyacetone synthase activity appeared after incubation of the strains in the medium with glycerol and methylamine but not with methanol. One of the mutants (W218) with the reduced activity of alcohol oxidase lacked the formate dehydrogenase activity (FDH−). All these mutants produced a low level of extracellular formaldehyde from methanol. The second and third types of mutants were deficient in dihydroxyacetone synthase (DAS−; 349, 409, 450), and dihydroxyacetone kinase (DAK−; 4D1, 4D3, 4D16) activities, respectively. DAK− mutants showed both the high activities of alcohol oxidase and NADH-dependent reduction of CH2O catalyzed by alcohol dehydrogenase. This indicated the possibility that NADH, generated in the oxidation of formaldehyde to CO2, may be oxidized by molecular oxygen via a futile cycle composed of the alcohol oxidase and alcohol dehydrogenase.