<p> 1Supporting online material J Bacteriol</p><p>2Movie S1</p><p>3Bdellovibrio growth-phase cells septate synchronously in bdelloplasts. Time-lapse movie </p><p>4showing a bdelloplast of an infected fluorescent prey cell with a dark growing Bdellovibrio cell </p><p>5within; this cell elongates from both poles until it reaches its maximum length and septates </p><p>6synchronously into 5 progeny, which lyse the bdelloplast resulting in the loss of fluorescence </p><p>7activity. Contrast shifts within the bdelloplast are likely due to shifts in the prey cytoplasmic </p><p>8membrane. Images were captured every 2.5 min and shown at 7 frames per second, scale bar = 1 </p><p>9µm. </p><p>10Movie S2</p><p>11Two separate Bdellovibrio growth-phase cells synchronously septate in doubly infected </p><p>12bdelloplasts. Time-lapse movie showing a bdelloplast of an infected fluorescent prey cell with </p><p>13two separate dark growing Bdellovibrio cells within; these cells elongate from both poles, until </p><p>14they reach their maximum length and septate synchronously into a total of 7 progeny (4 from the </p><p>15lower and 3 from the upper cell), which lyse the bdelloplast resulting in the loss of fluorescence </p><p>16activity. Growing cells seem to favour the bdelloplast periphery, presumably due to an unseen </p><p>17obstacle (for example the prey cell cytoplasm) in the centre; this inhibition seems to be released </p><p>18in the final stages of septation. Images were captured every 2.5 min and shown at 7 frames per </p><p>19second, scale bar = 1 µm.</p><p>20Movie S3</p><p>21Long Bdellovibrio growth-phase cells initiate septation synchronously in bdelloplasts. Time-</p><p>22lapse movie showing a bdelloplast of an infected fluorescent prey cell with a dark growing </p><p>23Bdellovibrio cell within; this cell elongates from both poles until it reaches its maximum length </p><p>1 1</p><p>2 24and initiates septation synchronously along an extended filament which will ultimately generate </p><p>258 progeny. Right hand pole of the elongating Bdellovibrio cell seems to get caught on an unseen </p><p>26obstacle, which is released in the later stages of growth. Contrast shifts within the bdelloplast are </p><p>27likely due to shifts in the prey cytoplasmic membrane. Growing cells seem to favour the </p><p>28bdelloplast periphery, presumably due to an unseen obstacle (for example the prey cell </p><p>29cytoplasm) in the centre; this inhibition seems to be released in the final stages of cell elongation.</p><p>30Images were captured every 2.5 min and shown at 7 frames per second, scale bar = 1 µm.</p><p>31Movie S4 </p><p>32Stored tension within a Bdellovibrio growth-phase filament leads to dramatic re-orientation of </p><p>33progeny cells after synchronous septation. Time-lapse movie, showing a bdelloplast of an </p><p>34infected fluorescent prey cell with a dark elongated and coiled Bdellovibrio cell within; this </p><p>35growth-phase cell septates leading to a dramatic shift in orientation of the 5 progeny cells, only </p><p>36possible if septation was synchronous. Progeny cells lyse the bdelloplast resulting in the loss of </p><p>37fluorescence activity. Images were captured every 2.5 min and shown at 7 frames per second, </p><p>38scale bar = 1 µm.</p><p>39</p><p>40</p><p>41Movie S5</p><p>42Bdellovibrio enter prey cells and, some, rarely, do not elongate and divide to form new progeny </p><p>43cells. Time-lapse dual-channel movie of overlaid brightfield (red) and fluorescence (green) </p><p>44images, initial fluorescence bleaching shows an example of a single dark Bdellovibrio cell in a </p><p>45small, fluorescent, rounded bdelloplast. The Bdellovibrio cell does not elongate or septate, and </p><p>46persists in the bdelloplast eventually lysing it (leading to a loss of fluorescence activity) and the </p><p>3 2</p><p>4 47single cell is clearly seen escaping to the lower right of the frame. Images were captured every </p><p>482.5 min and shown at 7 frames per second, scale bar = 1 µm.</p><p>49</p><p>50Movie S6</p><p>51Mature Bdellovibrio progeny escape the bdelloplast through a single hole. Time-lapse movies of </p><p>52overlaid brightfield (red) and fluorescence (green) images, movie shows a bdelloplast of an </p><p>53infected fluorescent prey cell with a dark growing Bdellovibrio cell within, and is the same </p><p>54bdelloplast shown in Movie S1. The growing Bdellovibrio cell septates synchronously into 5 </p><p>55progeny, which lyse the bdelloplast resulting in loss of fluorescence activity; progeny cells are </p><p>56then seen leaving the now exhausted prey cell through a hole in the bottom of the bdelloplast. </p><p>57This pattern was seen in 88% of observed bdelloplasts (n=67). Images were captured every 2.5 </p><p>58min and shown at 7 frames per second, scale bar = 1 µm.</p><p>59Movie S7</p><p>60Time-lapse brightfield movie showing motile Bdellovibrio progeny cells within a bdelloplast, at </p><p>61maturation, after septation. Three Bdellovibrio progeny cells appear to scramble over one another</p><p>62and collide with the inner wall of the bdelloplast which is immobilised on a glass surface in </p><p>63Ca/HEPES buffer. Internal collisions occasionally distort the shape of the bdelloplast. Images </p><p>64were captured at 25 frames per second using the IPLab software (version 3.64) and are shown at </p><p>65the same rate, scale bar = 1 µm.</p><p>5 3</p><p>6</p>