About 10 μl of cell samples were mounted on a number 1.5, 24 × 50 mm (thickness of 0.16–0.19 mm) cover glass slide (Fisher or VWR). Cells were cushioned with a 3% (w/v) agarose gel pad to restrict the movement of the live cells. Cells were optically imaged using a Nikon Eclipse Ti inverted microscope equipped with crossed polarizers and a Photometrics CoolSNAP HQ2 CCD camera using a Nikon 100X oil objective lens. Phase-contrast images of bacterial cells were recorded with an exposure time of 50 ms using Nikon NIS Elements software. Multiple snapshots were collected for each experiment. All images were analyzed to measure the cell length in Oufti (54 (link)) using one single optimized parameter set and manual verification. Confidence intervals of the fraction of elongated cells for each mutant were computed from 1000 replicates of bootstrap resampling (55 ).
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