FIG. 3.
Physical properties of test organisms. (A) Buoyant densities of C. oligotrophus, Marinobacter sp. strain T2 (M. T2), and E. coli from their positions (arrows) in a 70:30 gradient of Percoll-seawater medium. Data are for standard density marker beads. (B) m of C. oligotrophus determined by the minimal-absorbance method (solid line). The broken line is the least squares fit to the data for an optical density of >0.06 and yields an m of 1.025. (C) Cell volume computed from dry mass by flow cytometry, buoyant density, and Xdry/Xwet (equation 3) with respect to Coulter Counter volume measured for the three species. The inset shows cell volumes of C. oligotrophus determined by flow cytometry compared with those determined by transmission (▾) and scanning (▿) electron microscopy (EM).