HYDROGENOSOMES OF METOPUS-CONTORTUS PHYSIOLOGICALLY RESEMBLE MITOCHONDRIA

The anaerobic free-living ciliated protozoon Metopus contortus is a gr azer in anoxic marine sediments. It does not possess mitochondria, but it does have specialized organelles termed hydrogenosomes which relea se hydrogen gas. The cationic lipophilic cyanine dye DiOC(7)(3) is an indicator of transmembrane potential. With the aid of confocal laser s canning microscopy (CLSM), the association of this dye with hydrogenos omes in situ was followed. Flow cytometric measurements showed that fl uorescence of the membrane potential dye decreased in response to an e levated pH, in the cell. CLSM also revealed localization of fluorescen ce of the calcium probe Flue 3-AM, and of the transmembrane pH gradien t probe BCECF-AM, within the lumen of the hydrogenosomes. In addition, hydrogenosomal inclusions were detected. X-ray microanalysis of these electron-dense granules revealed high levels of calcium, phosphate an d magnesium. It is concluded that M. contortus hydrogenosomes are calc ium stores, have a membrane potential, and an alkaline lumen. These ph ysiological features resemble those of mitochondria in aerobic protozo a.