Metal starvation triggers CetZ1-dependent cell shape changes in haloarchaea

De Silva RT, Ithurbide S and Duggin IG

University of Technology Sydney.

Microbial cell shape is a significant attribute that affects survival, and many species can change morphology to adapt to environmental change and stress. Model haloarchaeon Haloferax volcanii cells transition from plates to rods to optimise swimming motility, which requires the tubulin-like cytoskeletal protein CetZ1. The signals that trigger cell shape change via CetZ1 are not yet clear. We analysed cell shape changes in various nutrient-depleted media, and found that cells developed highly irregular elongated forms in response to depletion of metal nutrients. These shapes were substantially more diverse compared to the regular rod-shaped cells seen in motile cells. Remarkably, the addition of a solution containing 8 metals to complex growth medium (HvYPC) significantly improved culture growth, and the cells showed a uniform plate-shaped morphology compared to non-supplemented HvYPC that produces mixed elongated- and plate-cell types. The formation of elongated cells during trace element limitation was dependent on CetZ1, and the cell elongation defect of an in-frame knock-out of cetZ1 was rescued by expression of CetZ1 from a plasmid. Towards the goal of understanding how CetZ1 functions to control cell shape, we have adapted a set of modern fluorescent proteins for use in H. volcanii. A CetZ1-mTurquoise2 fusion showed cell elongation capacity and revealed a highly dynamic localisation pattern associated with cell elongation during metal depletion, indicating that a dynamic remodelling of the cell envelope occurs during cell elongation. The improved tools and growth conditions can be utilized for working with H. volcanii in research and biotechnology.