Fig. 3.

Cell–cell contact resulting from pilus retraction. Two examples are shown in which the tip of a pilus extended by an HfrH cell makes contact with another HfrH cell and retraction of the pilus draws the two cells together. In A, the pilus is extending in the first two frames and makes contact with a dividing cell in the third. (An arrowhead marks the member of the dividing pair contacted by the pilus.) Retraction draws the dividing cell closer in the 140-s frame, and it has rotated and flipped upward in the 178-s frame. By 232 s, the cells are in close contact. (Movie S5). In B, a pilus links a cell marked with an arrow to another marked with an arrowhead, initially just out of the frame. The two cells draw closer in the next four frames, and the upper cell flips down into the field of view. After a period of close contact, the two cells separate. (Movie S6.) Time is shown as seconds after the first frame. (Scale bars, 2 μm.)