FIGURE 1.

(a) The size distribution of Ymel grown to the midexponential phase (3.5 h) in the M9 medium supplemented with 0.4% glucose. The inset shows a typical image with the scale bar of 5 μm. The size distribution can be mimicked reasonably well by a log-normal distribution as delineated by the solid line in the figure. Here μ = 1.38 is the mean of ln(L) and σ = 0.2 is its standard deviation. (b) The scattered light intensity-intensity autocorrelation function G₂(t) = 〈I(t′)I(t′ + t)〉/〈I(t′) 〉²−1 measured using λ-phage (pluses) and λ-phage heads (crosses) in the λ-buffer. The measurement was carried at room temperature T = 24°C and at the scattering angle of θ = 90°. This corresponds to the scattering wavenumber q(= 4πnsin(θ/2)/Λ) = 1.87 × 10⁵ cm⁻¹, where n is the index of refraction of water and Λ = 633 nm is the wavelength of the HeNe laser. The data shows that the phage tail does not contribute significantly to the decay of the autocorrelation function; i.e., the diffusion constant is essentially determined by the phage head. As can also be seen in the figure, for early times G₂(t) decays exponentially and can be compared to the theoretical predictions for spheres diffusing in a medium with viscosity η: G₂(t) = exp(−2D₃q²t), where D₃ = k_BT/6πηR is the diffusion coefficient for the sphere of radius R. This measurement yields the hydrodynamic radius R = 35 nm. The inset in the upper corner is the plot of the measured shear viscosity η for the λ-buffer, which is essentially the same as water. The lower inset is an electron microscopy image of intact λ-phage. Here the scale bar is 50 nm (courtesy of R. Hendrix).