ESCRT-III homolog PspA shapes membrane architecture and multicellularity in magnetoglobule bacteria

Abstract Endosomal Sorting Complex Required for Transport (ESCRT)-III proteins are crucial for membrane remodeling and repair across all domains of life. Eukaryotic ESCRT-III and cyanobacterial homologs such as Phage shock protein A (PspA) and Vipp1/Imm30 remodel membranes into diverse structures, including vesicles, rings, filaments, tubular rods, and multivesicular bodies (MVBs). Here, our microscopy analysis reveals that multicellular magnetoglobules possess elaborate compartments, including magnetosome organelles, polyphosphate granules, and various membrane structures, such as vesicles, rings, tubular rods, filaments, and MVB-like formations. This complexity suggested that membrane-remodeling PspA might be essential for their compartmentalization, morphogenesis, and the evolution of multicellularity. We generated nine magnetoglobule genomes, uncovering significant expansion relative to unicellular magnetotactic bacteria. Phylogenetic analysis implied that multicellular magnetoglobules might share a common ancestor with unicellular magnetotactic bacteria and undergone differentiation, forming two morphologies. Furthermore, PspA was ubiquitous in magnetoglobules, forming a distinct clade within bacterial and archaeal ESCRT-III phylogeny. All phylogenetic evidence suggested their evolution from a unicellular ancestor within the phylum Desulfobacterota. Heterologous expression of magnetoglobule pspA2 in Escherichia coli resulted in PspA2 localized at the poles in rod-shaped unicells and with a dispersed distribution in filamentous cells. Cryo-electron tomography of PspA2-expressing cells revealed filament bundles, membrane sacculi, vesicles, and MVB-like structures. Furthermore, electron-dense foci, mirroring the PspA2 distribution in filamentous cells, altered the inward orientation of the septum, potentially interfering with cell division. Collectively, these results demonstrate the membrane-remodeling function of magnetoglobule PspA proteins and suggest that they may contribute to the morphogenesis and evolution of multicellularity in magnetotactic bacteria.