Fig. 2.

Transmission electron microscopy images of Deianiraea bacteria on the surface of P. primaurelia CyL4-1 cells. a Portion of Paramecium cell surrounded by a huge number of extracellular Deianiraea bacteria, forming multiple layers. Bacterial cells appear electron dense, irregularly arranged, and sectioned in variably oriented planes. b–d Details of Deianiraea cells at higher magnification. In (b) and (c) longitudinal sections of some Deianiraea cells are shown. The bacterial side proximal to the Paramecium cell progressively narrows, ending up in a sharp and slightly curved apical tip, which takes direct contact with the external side of the Paramecium cell membrane (black arrowheads). In (d) a dividing Deianiraea cell, with the division septum highlighted by a black arrow. The few residual Paramecium cilia are evidenced by black asterisks in (b, d) sectioned from variable angles. Scale bars stand for, respectively, 1 μm (a) and 200 nm (b–d)