Establishing Rod-Shape from Spherical, Peptidoglycan-Deficient Bacterial Spores

Abstract

18Chemical-induced spores of the Gram-negative bacterium Myxococcus xanthus are 19 peptidoglycan (PG)-deficient. It is unclear how these spherical spores germinate into 20 rod-shaped, walled cells without preexisting PG templates. We found that germinating 21 spores first synthesize PG randomly on spherical surfaces. MglB, a GTPase activating 22 Significance 30Spheres and rods are among the most common shapes adopted by walled bacteria, in which 31 the peptidoglycan (PG) cell wall largely determines cell shape. When induced by chemicals, 32 rod-shaped vegetative cells of the Gram-negative bacterium Myxococcus xanthus thoroughly 33 degrades their PG and shrinks into spherical spores. As these spores germinate, cells rebuild 34 rod-shaped PG without preexisting templates, which provides a rare opportunity to visualize de 35 novo PG synthesis and bacterial morphogenesis. In this study, we investigated how spherical 36 spores elongation into rods during germination and elucidated a system for rod-shape 37 morphogenesis that includes the Rod PG synthesis system, a GTPase-GAP pair, the MreB 38 cytoskeleton and a molecular motor. 4Morphogenesis is a fundamental problem in biological systems. Compared to symmetric 40 spheres, rods are asymmetric and polarized. For most rod-shaped bacteria, the 41 peptidoglycan (PG) cell wall defines cell geometry, which is synthesized by two major 42 enzymatic systems. The Rod system consists of RodA, a SEDS-family PG polymerase, 43 PBP2, a member of the class B penicillin-binding proteins (bPBPs), and MreB, a 44 bacterial actin homolog (1-3). MreB orchestrates PG growth by the Rod complexes in 45 response to local cell curvature (4-9). In contrast, class A PBPs (aPBPs) contribute to 46 PG growth independent of MreB (10, 11). 47