FIG. 4.
RpoS protein level in bacteria at different culture densities. (A) Western blotting using anti-ςs antibodies was undertaken for extracts of bacteria grown at different cell densities in a glucose-limited chemostat at a dilution rate of 0.3 h−1. Tracks 1 to 4 contain MC4100 cultures at cell densities of 0.22 × 109, 0.45 × 109, 0.76 × 109, and 1.1 × 109 cells/ml, respectively. (B) Relative amount of RpoS protein as a function of cell density. Protein level was quantitated from densitometer scans using ImageQuant software in three separate blots, each containing samples from separate chemostat cultures of MC4100 growing at a dilution rate of 0.3 h−1 and with different steady-state densities. Samples were extracted by the ammonium sulfate precipitate method (●, ▿) or made using SDS extracts (▵). Quantitations were relative to the amount of RpoS found in bacteria grown with 0.02% glucose input in each series of experiments, which was set as 1.