Comparative, quantitative proteomic analysis of cell shape transitions in Haloferax volcanii

Cell shape plays a crucial role in microbial survival. While Haloferax volcanii, a model haloarchaeon, forms rods and disks, depending on environmental conditions, little is known about mechanisms underpinning archaeal cell-shape determination. We identified mutants that exclusively form rods and carried out comprehensive proteomics studies in which we compared these mutants to previously identified disk-only mutant strains and wild-type. Using this approach, we identified several additional candidates for shape determination. The generation of deletion mutants lacking genes encoding potential rod- and disk-determining factors, HVO_2174 (RdfA) and HVO_2176 (DdfA), respectively, resulted in rod- and disk-defective phenotypes. Comprehensive proteomics performed with ∆rdfA and ∆ddfA on these shape mutants implicated a diverse set of proteins, including transporters, signaling components, and transducers, as important for cell shape determination. We also identified structural proteins including the H. volcanii actin homolog volactin (VolA), a previously unknown cytoskeletal element, required for disk-shape morphogenesis.