FIG. A1.

Relationship between culture mass density and OD. A culture with an OD₄₆₀ = 0.812 was diluted to 0.2, 0.4, etc. (relative concentrations on abscissa), and the OD₄₆₀ of these dilutions was determined (points on the curve). The curve shown is a parabola that has been calculated (equation 7, with b = 0.15). The parabolic relationship can be used to find exact mass densities (triangles, curve labeled M) of cultures from the observed OD (see text for details). obs., observed; calc., calculated; Relat., relative.