FIG. 1.

Sedimentation of msbA conditional mutant WD2 cells on a Ludox density gradient. Mutant WD2 and parent E. coli W3110A cells were grown and analyzed using a Ludox density gradient as described in the text. (A) Photograph of the centrifuge tubes following centrifugation. Arrows show the area where most cells are found. (B) Light scattering of each fraction was measured by recording the A₆₀₀ of individual diluted samples. Fractions from an identical blank gradient were used to subtract background absorbance. Black circles refer to A₆₀₀ of fractions from gradient containing W3110A cells, and squares refer to WD2. O.D ₆₀₀, optical density at 600 nm. (C) Equal volumes of pooled fractions 1, 2, and 3 (arrows in panel B) from W3110A (left plate) or WD2 (right plate) tubes were plated to assess relative CFU levels recovered from the gradient and to demonstrate cell viability. Plates were incubated at 30°C overnight.