Fig. 3.

Association of V. fischeri cells with cilia on the surface of the light organ. (A, B) TEM images of cells of V. fischeri strain MB13B2, demonstrating structurally altered cilia in areas where bacteria directly interact with the ciliated surface of the light organ. (A) Upper panel: low magnification, showing the relationship of aggregating V. fischeri cells to the host’s ciliated epithelium; b, bacteria; c, structurally altered cilia. Lower panel: boxed area (rotated 90˚ clockwise) at higher magnification; altered cilia with swollen, paddle-shaped tips (green arrows) in association with V. fischeri cells. (B) High-magnification image, showing typical features of distorted cilia tip. (C-E) Confocal images at increasing magnification reveal host-cilia interactions with MB13B2 cells. (C) Low magnification, showing whole light organ. (D) Three-fold higher magnification of boxed area in C, showing aggregating bacteria. Yellow area indicates the co-localization of cilia (green) and V. fischeri cells (red). (E) Five-fold higher magnification than D, with only the green laser channel active to show the structurally altered cilia (green threads with terminal paddles) that form in areas of bacterial association (white arrows). The upper sector of this image shows structurally unaltered cilia for comparison (F) High-magnification confocal image of the ciliated surface of an aposymbiotic animal, where only an occasional cilium has an altered tip (inset, lower left); aa, anterior appendage; pa, posterior appendage; p, pore. Green,Tubulin Tracker; blue, WGA (wheat-germ agglutinin) Alexa 633.