Isolation and Characterization of Mutants of the Methylotrophic Yeast, Candida boidinii S2 That Are Impaired in Growth on Peroxisome-Inducing Carbon Sources

Candida boidinii is a methylotrophic yeast that grows well on oleic acid, D-alanine, or methanol as sole carbon sources. All of these growth substrates induce peroxisomal proliferation; we refer to them as PICs (Peroxisome Inducing Carbon sources). While the activity of catalase, an important peroxisomal enzyme, was induced by all the PICs, peroxisomal oxidases were induced in a PIC-specific manner. To better understand peroxisomal proliferation, two mutant strains that completely lost the ability to grow on all of the PICs were isolated and analyzed. Peroxisome matrix enzymes (catalase, D-amino acid oxidase, alcohol oxidase, etc.) in both mutant strains were mislocalized to the cytosol, and they were active there. Electron microscopy revealed the lack of normal large methanol-induced peroxisomes. We conclude that these mutants are impaired in peroxisomal assembly. Furthermore, the two mutants differed in the catabolite inactivation response to glucose. Finally, although both mutant strains could not grow on D-alanine as a carbon source, they could use D-alanine as a single nitrogen source. Thus, peroxisome assembly seemed to be important for the growth of C. boidinii on all of the PICs.