Physiological role of stalk lengthening in Caulobacter crescentus

The Gram-negative bacterium Caulobacter crescentus forms a thin polar stalk, which mediates its attachment to solid surfaces. Whereas stalks remain short (1 µm) in nutrient-rich conditions, they lengthen dramatically (up to 30 µm) upon phosphate starvation. A long-standing hypothesis is that the Caulobacter stalk functions as a nutrient scavenging "antenna" that facilitates phosphate uptake and transport to the cell body. The mechanistic details of this model must be revisited, given our recent identification of a protein-mediated diffusion barrier, which prevents the exchange of both membrane and soluble proteins between the stalk extension and the cell body. In this report, we discuss the potential of stalks to facilitate nutrient uptake and propose additional physiological roles for stalk elongation in Caulobacter cells.