Fig. 3

Cell density of the M. luteus strains trpE16, ope and ΔoleABCD:kan, determined by centrifugation to equilibrium in self-generated gradients of Percoll. a Top, density gradient of Percoll, formed by centrifugation of a 65% Percoll solution in 0.15 M NaCl (starting ρ = 1.09 g × ml⁻¹) for 30 min at 23,000×g and 20 °C. The density was determined by measuring the refractive index with a digital refractometer of samples collected at the indicated positions, using a standard curve supplied by the manufacturer. Bottom, a representative result from the banding observed with cells of the indicated M. luteus strains, resuspended in 0.15 M NaCl and centrifuged at the above conditions. (B) Cell density of the M. luteus strains trpE16, ope and ΔoleABCD:kan (mean ± SD), determined by equilibrium centrifugation in self-generated Percoll gradients. The individual measurements from 6 centrifugations of cells from each strain are shown (*** significant at p ≤ 0.001, **** significant at p ≤ 0.0001, Welch’s unequal variances t-test)