The wall-less bacterium builds a polymeric cytoskeleton composed of interacting MreB isoforms.

A rigid cell wall defines the morphology of most bacteria. MreB, a bacterial homologue of actin, plays a major role in coordinating cell wall biogenesis and defining cell shape. are wall-less bacteria that robustly grow with a characteristic helical shape. Paradoxal to their lack of cell wall, the genome contains five homologs of MreB (SpMreBs). Here, we investigate the function of SpMreBs in forming a polymeric cytoskeleton. We found that, , maintain a high concentration of all MreB isoforms. By leveraging a heterologous expression system that bypasses the poor genetic tractability of , we found that SpMreBs produced polymeric filaments of various morphologies. We characterized an interaction network between isoforms that regulate filament formation and patterning. Therefore, our results support the hypothesis where combined SpMreB isoforms would form an inner polymeric cytoskeleton that shapes the cell in a wall-independent manner.