Hydrogenosomes in the rumen entodiniomorphid ciliate Polyplastron multivesiculatum

Abstract

The rumen entodiniomorphid ciliate protozoon Polyplastron multivesiculatum was shown, by biochemical and electron microscopic techniques, to possess hydrogenosomes. After differential centrifugation of whole cell homogenates the hydrogenosomal marker enzymes pyruvate: ferredoxin oxidoreductase and hydrogenase were recovered predominantly (61% and 70% of activity respectively) in the large granular fractions that were sedimented by centrifugation for 104 g-min (fraction P1) and 105 g-min (fraction P2). These subcellular fractions contained membrane-bound organelles that were approximately 0·4–0·6 μm in diameter and which had a mean equilibrium density of 1·22–1·24 g ml−1 after isopycnic centrifugation in sucrose gradients. Malate dehydrogenase (decarboxylating) activity, however, was predominantly non-sedimentable after centrifugation for 6 × 106 g-min. Numerous hydrogenosome-like organelles were present in the ectoplasm and endoplasm of the cell. Hydrogenase activity was demonstrated and localized in the protozoan cell using a novel staining procedure with distyryl nitroblue tetrazolium chloride (DSNBT).