(a) Graphs showing the average roundness coefficient of bdelloplasts from phase contrast images. Roundness analysis was carried out on wild-type and endopeptidase knockout-mutant Bdellovibrio infected E. coli prey cells heterologously expressing Bd3460. Images were taken 90 min post-invasion and the roundness of infected prey cells were analysed using ImageJ software. Roundness of bdelloplasts is reduced in all cases by IPTG induction of bd3460. A negative control of induction of bd1180, a different ankyrin repeat protein, did not reduce roundness, giving values similar to wild type (0.85 c.f. 0.90 published in Lerner et al.6) Error bars show 95% confidence intervals and statistical analysis of the means were compared with WT (*P<0.05; ***P<0.001 as determined by Student’s t-test). Data are taken from at least two independent experiments (n>60). (b) Histograms of mean times for attachment (lefthand panel) and invasion (righthand panel) by B. bacteriovorus HD100 wild type (straight line fill), ΔBd0816 (diagonal line fill) and ΔBd3459 (solid fill) strains infecting E. coli S17-1 (pBd3460). Mean attachment time was measured from initial Bdellovibrio contact with the outside of prey cell to the start of traversal through the prey cell wall. Mean invasion time was measured from the start of traversal through the prey cell wall to not being visible outside the prey cell, that is, being completely within the prey cell. At least two independent experiments were carried out (n>50) with error bars showing 95% confidence intervals and statistical analyses shown (**P<0.01 ***P<0.001 in Student’s t-test).