Figure 6: β-P153L renders loss of rod shape non-lethal in rich media.
A) β-P153L is highly resistant to both mecillinam and A22, with MICs for both antibiotics that are higher by at least an order of magnitude. Maximum OD600 (ODmax) was extracted from growth curves of β-P153L (red curves) and its parental control (black curves) and normalized by the ODmax of each strain in the absence of antibiotic. Error bars represent 95% confidence intervals.
B) In the parental strain growing on agarose pads with LB+10 μg/mL mecillinam, division rapidly halted and cells expanded dramatically in volume, with the formation of apparent membrane invaginations (red arrows) and eventual lysis.
β-P153L cells growing on agarose pads with LB+10 μg/mL mecillinam lost rod-like shape but remained small and continued dividing without lysis. Elapsed time since imaging started is indicated in hours and minutes (H:MM) using white lettering at the top left of each panel. Scale bar: 5 μm.
C) β-P153L suppresses the lethality of ΔmreB in rich media. The ΔmreB deletion was introduced into the backgrounds of β-P153L and its parental control under permissive conditions (M9 minimal medium at 30 °C). Growth curves were measured after transitioning these strains to non-permissive conditions (LB at 37 °C). Left: ΔmreB halted bulk growth after a transition to non-permissive conditions. Right: β-P153L ΔmreB retained luxuriant growth in LB. The average OD600 from multiple growth curves is shown as an opaque line. The 95% confidence interval is shown is shown as a shading with the same color.