An assessment of methods for measuring volumes of planktonic bacteria, with particular reference to television image analysis

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Abstract
Several methods for measuring volumes of planktonic bacteria were compared. The eyepiece micrometer grossly overestimated cell width (47–65%) and hence volume (73%). Shrinkage occurred with scanning electron microscopy, so volumes were underestimated by about 77%. All the other methods gave similar results (mean volume = 0.133 µm3). The optimum technique was to filter acridine orange stained bacteria through polycarbonate membrane filters (0.2 µm) which were photographed with epifluorescence microscopy using Kodak Tri‐X pan film. We recommend that volumes are estimated from individual area and perimeter measurements of at least 200 bacteria with a Quantimet 800 or Q10 image analyzer.