Abstract
A fundamental question in biology is how cell shapes are genetically encoded and enzymatically generated. Prevalent shapes among walled bacteria include spheres and rods. These shapes are chiefly determined by the peptidoglycan (PG) cell wall. Bacterial division results in two daughter cells, whose shapes are predetermined by the mother. This makes it difficult to explore the origin of cell shapes in healthy bacteria. In this review, we argue that the Gram-negative bacterium Myxococcus xanthus is an ideal model for understanding PG assembly and bacterial morphogenesis, because it forms rods and spheres at different life stages. Rod-shaped vegetative cells of M. xanthus can thoroughly degrade their PG and form spherical spores. As these spores germinate, cells rebuild their PG and reestablish rod shape without preexisting templates. Such a unique sphere-to-rod transition provides a rare opportunity to visualize de novo PG assembly and rod-like morphogenesis in a well-established model organism.
Highlights
And BacterialWhile spheres may seem simple and physically preferable, cells are seldom spherical.Instead, most cells invest extra energy to establish and maintain non-spherical shapes through a process known as “morphogenesis”
Phylogenic studies suggest that the common ancestor of bacteria was rod-shaped, and that rod-like shapes are advantageous for cell survival [1,2,3]
As PG is usually essential for bacterial survival, and its assembly systems are well conserved in most bacteria, including M. xanthus [23], M. xanthus provides unique opportunities to better understand the mechanisms of PG
Summary
While spheres may seem simple and physically preferable, cells are seldom spherical. Instead, most cells invest extra energy to establish and maintain non-spherical shapes through a process known as “morphogenesis”. L-form cells of both Bacillus subtilis and Escherichia coli can rebuild rods when their genetic defects are rescued, which provides potential vehicles for the study of the de novo generation of non-spherical shapes [16,17]. These PG-deficient cells usually take on an array of irregular shapes, especially during proliferation, which makes reproducible live-cell imaging technically challenging [16,17,18]. In response to certain chemicals, individual M. xanthus cells can degrade their PG thoroughly and form spherical spores [21,22] During germination, these spores restore vegetative morphology by assembling rod-shaped PG de novo. As PG is usually essential for bacterial survival, and its assembly systems are well conserved in most bacteria, including M. xanthus [23], M. xanthus provides unique opportunities to better understand the mechanisms of PG assembly and rod-like morphogenesis
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