Growth of Azotobacter vinelandii with correlation of Coulter cell size, flow cytometric parameters, and ultrastructure.

When Azotobacter vinelandii is grown under nitrogen-fixing conditions, the mean cell volume fluctuates from 2.7 to 6.6 microns 3 as determined using a Coulter counter. When NH4Cl is supplied as nitrogen source, the mean cell volume fluctuates from 4.6 to 7.4 microns3. Parallel experiments using flow cytometric measurements show similar characteristic fluctuations in the narrow forward angle light scattering signal and also in cellular protein content as determined using fluorescein isothiocyanate (FITC) fluorescence. Fluctuations in the perpendicular light scatter signal during batch growth are similar for both sets of growth conditions. Changes in cell morphology and ultrastructure are also similar for both sets of growth conditions, as demonstrated by electron microscopic examination. We conclude that narrow forward angle light scatter is a close correlate of cell size, whereas right angle scatter is an indicator of morphological variations other than size.