TEE FXYDROGENOSOME

M. Benchimolr, W. DeSouza’, Almeida, J.C. A’.

R Jomalista Orlando Dantas, 59p0 andar. Botiogo-CEP 22231-010. R J., Brazil. %stituto de Biotica Carlos Chagas Filho. UlW. Rio de Janeiro. Brazil.

During the evolutionary process eukaryotic microorganisms appeared presenting special cytoplasmic organelles. One example is the hydrogenosome initially found in protozoa of the Trichomonadida order and which contains enzymes that participate in the metabolism of pyruvate formed during glycolysis and was the site of formation of molecular hydrogen and ATP (Miiller, 1993). Later on this organelle was described in some fungi, in a number of anaerobic rumen ciliates and very likely in certain free&ing ciliates. The hydrogenosomes were described as spherical or slightly elongated granules with 0.5-2.0 urn diameter (Fig. l), closely associated to cytoskeletal structures such as the axostyle and costa. We have shown that two closely apposed unit membranes envelop the hydrogenosome and also a flattened, membrane-bounded vesicle at the periphery of the hydrogenosome (Figs. 2-3). Analysis of thin serial sections used to 3-D reconstruction and fieeze&acture replica show that the hydrogenosome resembles a sphere, but presents a protrusion towards the cytoplasm (Fig.4). The vesicle presents a distinct morphological appearance from the hydrogenosome matrix, was the main site of Ca*-accumulation, presents phosphatase activity, its membrane presents N-acetyl-glucosamine- containing glycoconjugates, and is obtained by sequential treatment of the hydrogensosomal traction, we conclude that it represents a specialized sub-compartment of the hydrogenosome. The morphogenesis of hydrogenosomes was investigated by transmission electron microscopy of thin sections and freeze-fracture replicas of whole cells or the isolated organelle. Close proximity, and even continuity, between endoplasmic reticulum and hydrogenosomes was observed. Morphological evidence shows that hydrogenosomes, like mitochondria, may divide by two distinct processes: segmentation and partition. In the segmentation process, the hydrogenosome grows, becoming elongated with the appearance of a constriction in the central portion. Microfibrillar structures appear to help the furrowing process, ending with a total fission of the organelle. In the partition process, the division begins by an invagination of the inner hydrogenosome membrane, forming a transversal septum, separating the organelle matrix into two compartments. The structure of hydrogenosomes of the anaerobic fungus NeocaZZimastixfiontaZis was also analyzed. They appeared enveloped by two distinct, but tightly apposed membranes. These observations suggest that hydrogenosomes are homologous organelles in unrelated species weakening the hypothesis of a polyphyletic origin and support the evidence that fimgal hydrogenosomes are probably derived from an endosymbiont relationship.

Supportedby: FENORTE, FINEP, CNPq, AUSU. References: Mtiller M., The Hydrogenosome. J&n. Microb. 139, (1993) 2879

Figure 1. General view of Tritichomonas fmtus in a routine thin section. II, Hydrogenosomes; N, Nucleus. X 18,000. In fig. 2 the star shows the calcium deposit in the flat vesicle whereas in fig.3 the flat vesicle is apparently empty. The arrow point to the two closely apposed membranes of the hydrogenosome (I-l) X 110,000. Figure 4. View of fieeze-fiacture images of hydrogensosomes (II). Arrowhead points to the hydrogensomes (H) protusion. G, Golgi complex. X 66,000.