Fig. 1.

Micrograph of a C. crescentus cell and models of nutrient uptake. (A) Transmission electron micrograph of C. crescentus. F, flagellum; S, stalk; H, adhesive holdfast; D, division site. (B) Models of nutrient uptake by the stalk and cell body. The model in the top part of the diagram (thick arrows) illustrates uptake of a nutrient molecule into the stalk periplasm, its binding to a periplasmic nutrient-binding protein, the diffusion of the nutrient-binding protein from the stalk periplasm to the cell body periplasm, and the uptake of the nutrient into the cell body cytoplasm by an ABC transporter. This periplasm-to-periplasm model is consistent with our results. The model on the bottom part of the diagram (thin arrows) illustrates nutrient uptake into the stalk core, followed by its diffusion into the cell body cytoplasm. Nutrient uptake in the cell body is also shown (intermediate-thickness arrows).