Cell-to-cell interactions suggesting a sexual process in Herpetomonas megaseliae (Kinetoplastida: Trypanosomatidae)

Giemsa-stained smears of Herpetomonas megaseliae cultures in LIT medium displayed on several occasions not only the typically dividing promastigotes but also pairs of apposed parasites attached by their posterior ends, where a cellular enlargement and a ring-like border generally occurred; other pairs formed by an elongated promastigote and a bell-shaped cell were also found. In both cases, either each of the joined cells could have its own nucleus or one of them was anucleate and the other presented two nuclei that were sometimes so close that they appeared to be a single nucleus. These findings, along with others seeming to be intermediate steps between them, strongly suggested that a sexual process, involving parasite union followed by nuclear migration from one cell to the other and then by fusion, was taking place in such cultures.