Figure 2.

Models for the microscopy images of spheroidal protein shells. (a) The geometry of a spherical fluorescent shell of radius a can be used to establish an equation for the radial intensity distribution of its fluorescence image, f(r). (b) A sample image generated by f(r). (c) A more general plot detailing how f(r) varies with the radius of the microscope PSF. Note that the contour of maximum image brightness lies inside the shell radius, due to blurring by the microscope. The cubehelix color map, which is linear in perceived brightness and maximally distinct in color, is ideal for visualizing the function (26). (d) A typical, real fluorescence image of B. megaterium can be very effectively fitted by f(r). (e–g) A Monte Carlo model of a spherical fluorescent coat layer generates images similar to those generated by f(r), and can be adapted to simulate elongated spores either by stretching the sphere into an ellipsoid, which results in relatively denser fluorescent molecules at the poles (f) or sampling an ellipsoidal shell with uniform fluorescent labeling density (g). Real images of elongated spores often lie between cases (f) and (g). (h) Coordinate system for the ellipsoidal model. To see this figure in color, go online.