FIG 6.

Transmission electron microscopic images of Paramecium biaurelia isolate US_Bl 11III1. (A) For this isolate, the secondary symbiont “Candidatus Fokinia cryptica,” indicated by black arrows, was observed in cooccurrence with “Candidatus Bealeia paramacronuclearis.” (B) “Candidatus Bealeia paramacronuclearis” was frequently surrounded by host lysosomes (white asterisks). (C and D) Parts of the host's digestive vacuole (food vacuole [FV]) containing bacteria morphologically similar to “Candidatus Bealeia paramacronuclearis” were seen to bud off, producing vesicles enclosing them. Scale bars, 0.5 μm (A, B, and D) or 1.0 μm (C).