MONITORING OF PEROXISOME INDUCTION AND DEGRADATION BY FLOW CYTOMETRICANALYSIS OF HANSENULA-POLYMORPHA CELLS GROWN IN METHANOL AND GLUCOSE MEDIA - CELL-VOLUME, REFRACTIVE-INDEX AND FITC RETENTION

Cell refractive index has been used to monitor peroxisome behaviour in the yeast Hansenula polymorpha by means of flow cytometry. Peroxisome s are inducible organelles which may occupy a large fraction of the ce ll volume when yeast cells are growing in methanol media. These organe lles harbour a catalase that decomposes the hydrogen peroxide produced in methanol oxidation by alcohol oxidase, a peroxisomal enzyme whose subunits are arranged to form a regular crystalloid. Peroxisomes under go a degradation process mediated by vacuoles whenever they and their enzymes become metabolically redundant (e.g. during growth on glucose) . Flow cytometric analyses of side scattered light (depending on cell volume, morphology and structure) and fluorescein isothiocyanate reten tion (due to the vacuole) were made on two wild-type strains of H. pol ymorpha during exponential growth in glucose and methanol media and du ring nutritional shifts from one carbon source to the other. The same parameters were also analysed for a mutant strain only partially repre ssed by glucose. We show that both the parameters are substrate-depend ent and appear to reflect peroxisome development in the cells. The dat a reported correlate well with the known cytological and biochemical d ata, showing the possibility of using flow cytometry, a fast and sensi tive technique, to analyse the dynamics of peroxisome proliferation an d degradation in response to environmental as well as genetic factors.