Archaeal Cytoskeletal Protein CetZ1 Influences Assembly of the Motility Machinery.

The archaeal tubulin-like cytoskeletal protein CetZ1 is required for rod-cell morphogenesis during the development of motility in Haloferax volcanii. This is expected to improve swimming speed and directionality. Here, we found that deletion of cetZ1 or expression of a GTPase-defective mutant caused the expected defects in cell shape, and also resulted in a substantial defect in the assembly of the motility machinery, including the archaellum base marker protein ArlD1, the chemotaxis sensory array adapter CheW1, and signal transducer CheY. Interestingly, moderate overexpression of cetZ1 (by 2-3 fold) reduced motility and the assembly and polar placement of the motility machinery without detectably affecting the rod shape of motile cells. We also investigated deletion of the conserved paralog cetZ2, which caused no detected defects in swimming or rod shape. However, overexpression of cetZ2 caused mild hyper-motility, whereas the cetZ2 GTPase-defective mutant reduced motility; these effects were dependent on the presence of cetZ1, suggesting that the altered cetZ2 might interfere with CetZ1's role in motility. Finally, we saw that a functional CetZ1-mTurquoise2 fusion strongly localized at the poles of mature motile cells, where it partially co-localized with the motility machinery markers. Overall, our results suggest that roles of CetZ1 in cell shape or potentially the organisation and structure of the cell poles influence the polar assembly of the motility machinery.