CA2- A MITOCHONDRIAL-LIKE PHYSIOLOGICAL-ROLE( ACCUMULATION IN THE HYDROGENOSOMES OF NEOCALLIMASTIX FRONTALIS L2 )

The anaerobic fungus Neocallimastix frontalis L2 does not carry out ox idative phosphorylation but instead obtains energy from a fermentative metabolism. It does not have mitochondria, but does contain specialis ed redox organelles, the hydrogenosomes. With the aid of confocal lase r scanning microscopy, we were able to follow the compartmentalisation of the Delta pH probe BCECF-AM -propyl-5-oxoisoxazol-4-yl)pentamethin e(oxonolVi), 2',7'-bis(2-carboxyethyl)-5-carboxyfluorescein acetomethy l ester) into hydrogenosomes in situ. Association of the Ca2+-specific dye Fluo-3AM (1-[2-amino-5-(2,7-dichloro amino-5-methylphenoxy]ethane -N,N,N',N'-tetraacetic acid acetomethyl ester) within the lumen of the hydrogenosomes was also observed. In addition, transmission electron microscopy revealed that the hydrogenosomes contained electron-dense i nclusions. X-ray microanalysis of these granules indicated the presenc e of calcium and phosphate. Our results indicate that hydrogenosomes f rom N. frontalis L2 maintain an internal alkaline pH and are involved in the calcium regulation of the cell. These physiological features re semble those of mitochondria from aerobic fungi.