Figure 4.

Cytoskeletons trigger new shapes in bacteria.

Shown are two examples of new shapes resulting from bacterial cytoskeletal proteins. (A) In Streptomyces, DivIVA (orange balls) forms large assemblies at the poles of hyphae, possibly recognizing a region of sharp membrane curvature, but also forms seemingly random foci along the sidewall. As DivIVA tends to self-assemble, larger foci are easily generated (middle panel). These larger assemblages probably trigger branch formation, because a DivIVA focus usually forms under a new pole prior to visible branch initiation. A DivIVA lattice is subsequently maintained at the new branch tip (green) and is required for continued tip extension. (B) Cells of Mycoplasma pneumoniae lack peptidoglycan, and would be spheroidal without a cytoskeleton (top). Cytoskeletal proteins form the terminal organelle, which is important for gliding motility (red rightward arrow); the resulting cell extension (red) upon movement and subsequent duplication of the organelle at the opposite pole (not shown) gives these wall-less cells a roughly cylindrical shape with narrow tips.