New associated structures of the anterior flagella of Giardia duodenalis.

Giardia duodenalis is a protozoan parasite that causes intestinal disorders. The trophozoites present four pairs of flagella. Here we further analyze the structural organization of the anterior flagella associated structures of G. duodenalis. High resolution scanning electron microscopy of detergent-extracted trophozoites revealed novel aspects of the interaction of the anterior flagella axonemes with the marginal plates. Images of the marginal plates showed that it was located in the anterior region of the parasite, above the crossing point of the anterior flagella axonemes toward the periphery of the cell. Two well distinguished structures were seen associated with the anterior flagella. The first one corresponds to the "dense rods", located just below the axoneme. The second one is a system of filaments located in the upper portion of the flagellum, facing the marginal plates and connecting these two structures. The thickness of the filaments is around 18 nm and they are spaced at intervals of 4-32 nm (average 18 nm). The length of the filaments may vary from 33 to 240 nm. We suggest that this filamentous structure of Giardia may help the dynamics and behavior of the anterior flagella of trophozoites during protozoan motility and adhesion, providing favorable conditions for the establishment of parasitism.