Fluorescence microscopic studies on mitochondria and mitochondrial nucleoids in a wild-type strain and respiratory mutants of Candida albicans.

A wild-type strain and two respiratory mutants of Candida albicans were examined for mitochondria and mitochondrial nucleoids (mt-nucleoids) using the fluorescent dyes, 2-(4-dimethylaminostyryl)-1-methylpyridinium iodide (DASPMI) and 4', 6-diamidino-2-phenylindole (DAPI). Rapidly growing cells of the wild type possessed one or a few giant branched mitochondria that were intensely stained with DASPMI. When a bud emerged, an end of the giant mitochondrion extended into the bud and the mitochondrion was divided and partitioned into mother and daughter cells by cytokinesis. Cell cycle-associated fragmentation or fusion of mitochondria were not demonstrated. The mutant KRD-8, that possesses cristate mitochondria but respires at a lower level, was shown to contain one or a few, less stainable giant mitochondria per cell. DASPMI failed to stain cells of the mutant KRD-19 which lacks cytochrome aa3 and cristate mitochondria. About eight and 10 mt-nucleoids were detected as discrete fluorescent spots in DAPI-stained cells of the wild type and KRD-8, respectively. KRD-19 cells also possessed mt-nucleoids, although the number of mt-nucleoids per cell seemed to be smaller than that of the wild type. In all the strains, mt-nucleoids existed discretely throughout the budding cycle, and the increase of their number per cell appeared to correlate with the cellular volume but not with nuclear division.