Bacteria-like endosymbionts in Blastocystis sp.

Bacteria-like endosymbionts were found in vacuolar cells and cysts of Blastocystis sp. from duck and monkey faecal material. The organisms ultrastructurally resembled Gram-negative bacilli, and were present in the nucleus of Blastocystis sp. from the duck and in the cytoplasm of Blastocystis sp. from the monkey. Based on size and differences in intracellular location, it is probable that these represent two distinct species of organisms.