Identification and characterization of structural and regulatory cell-shape determinants in Haloferax volcanii

Archaea play indispensable roles in global biogeochemical cycles, yet many critical cellular processes, including cell-shape determination, are poorly understood. Haloferax volcanii, a model haloarchaeon, forms rods and disks, depending on growth conditions. Here, we used a combination of iterative proteomics, genetics, and live-cell imaging to identify distinct mutants that only form rods or disks. We compared the proteomes of the mutants with wild-type cells across growth phases, thereby distinguishing between protein abundance changes specific to cell shape and those related to growth phases. The corresponding results indicated a diverse set of proteins, including transporters, transducers, signaling components, and transcriptional regulators, as important for cell-shape determination. We also identified structural proteins, including a previously unknown cytoskeletal element, the Hfx. volcanii actin homolog volactin, which plays a role in disk-shape morphogenesis. In summary, we gleaned important insights into archaeal cell-shape determination, with possible implications for understanding the evolution of cell morphology regulation across domains.