45 research outputs found
Cell-size maintenance: universal strategy revealed
How cells maintain a stable size has fascinated scientists since the
beginning of modern biology, but has remained largely mysterious. Recently,
however, the ability to analyze single bacteria in real time has provided new,
important quantitative insights into this long-standing question in cell
biology
Fundamental Principles in Bacterial Physiology - History, Recent progress, and the Future with Focus on Cell Size Control: A Review
Bacterial physiology is a branch of biology that aims to understand
overarching principles of cellular reproduction. Many important issues in
bacterial physiology are inherently quantitative, and major contributors to the
field have often brought together tools and ways of thinking from multiple
disciplines. This article presents a comprehensive overview of major ideas and
approaches developed since the early 20th century for anyone who is interested
in the fundamental problems in bacterial physiology. This article is divided
into two parts. In the first part (Sections 1 to 3), we review the first
`golden era' of bacterial physiology from the 1940s to early 1970s and provide
a complete list of major references from that period. In the second part
(Sections 4 to 7), we explain how the pioneering work from the first golden era
has influenced various rediscoveries of general quantitative principles and
significant further development in modern bacterial physiology. Specifically,
Section 4 presents the history and current progress of the `adder' principle of
cell size homeostasis. Section 5 discusses the implications of coarse-graining
the cellular protein composition, and how the coarse-grained proteome `sectors'
re-balance under different growth conditions. Section 6 focuses on
physiological invariants, and explains how they are the key to understanding
the coordination between growth and the cell cycle underlying cell size control
in steady-state growth. Section 7 overviews how the temporal organization of
all the internal processes enables balanced growth. In the final Section 8, we
conclude by discussing the remaining challenges for the future in the field.Comment: Published in Reports on Progress in Physics.
(https://doi.org/10.1088/1361-6633/aaa628) 96 pages, 48 figures, 7 boxes, 715
reference
Time scale of entropic segregation of flexible polymers in confinement: Implications for chromosome segregation in filamentous bacteria
We report molecular dynamics simulations of the segregation of two
overlapping chains in cylindrical confinement. We find that the entropic
repulsion between the chains can be sufficiently strong to cause segregation on
a time scale that is short compared to the one for diffusion. This result
implies that entropic driving forces are sufficiently strong to cause rapid
bacterial chromosome segregation.Comment: Minor changes. Added some references, corrected the labels in figure
6 and reformatted in two columns. Also added reference to published version
in PR
Bending forces plastically deform growing bacterial cell walls
Cell walls define a cell shape in bacteria. They are rigid to resist large
internal pressures, but remarkably plastic to adapt to a wide range of external
forces and geometric constraints. Currently, it is unknown how bacteria
maintain their shape. In this work, we develop experimental and theoretical
approaches and show that mechanical stresses regulate bacterial cell-wall
growth. By applying a precisely controllable hydrodynamic force to growing
rod-shaped Escherichia coli and Bacillus subtilis cells, we demonstrate that
the cells can exhibit two fundamentally different modes of deformation. The
cells behave like elastic rods when subjected to transient forces, but deform
plastically when significant cell wall synthesis occurs while the force is
applied. The deformed cells always recover their shape. The experimental
results are in quantitative agreement with the predictions of the theory of
dislocation-mediated growth. In particular, we find that a single dimensionless
parameter, which depends on a combination of independently measured physical
properties of the cell, can describe the cell's responses under various
experimental conditions. These findings provide insight into how living cells
robustly maintain their shape under varying physical environments
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Bending forces plastically deform growing bacterial cell walls
Cell walls define a cell shape in bacteria. They are rigid to resist large internal pressures, but remarkably plastic to adapt to a wide range of external forces and geometric constraints. Currently, it is unknown how bacteria maintain their shape. In this work, we develop experimental and theoretical approaches and show that mechanical stresses regulate bacterial cell-wall growth. By applying a precisely controllable hydrodynamic force to growing rod-shaped Escherichia coli and Bacillus subtilis cells, we demonstrate that the cells can exhibit two fundamentally different modes of deformation. The cells behave like elastic rods when subjected to transient forces, but deform plastically when significant cell wall synthesis occurs while the force is applied. The deformed cells always recover their shape. The experimental results are in quantitative agreement with the predictions of the theory of dislocation-mediated growth. In particular, we find that a single dimensionless parameter, which depends on a combination of independently measured physical properties of the cell, can describe the cell's responses under various experimental conditions. These findings provide insight into how living cells robustly maintain their shape under varying physical environments.Physic
Cell boundary confinement sets the size and position of the E. coli chromosome
Although the spatiotemporal structure of the genome is crucial to its biological function, many basic questions remain unanswered on the morphology and segregation of chromosomes. Here, we experimentally show in Escherichia coli that spatial confinement plays a dominant role in determining both the chromosome size and position. In non-dividing cells with lengths increased to 10 times normal, single chromosomes are observed to expand > 4-fold in size. Chromosomes show pronounced internal dynamics but exhibit a robust positioning where single nucleoids reside robustly at mid-cell, whereas two nucleoids self-organize at 1/4 and 3/4 positions. The cell-size-dependent expansion of the nucleoid is only modestly influenced by deletions of nucleoid-associated proteins, whereas osmotic manipulation experiments reveal a prominent role of molecular crowding. Molecular dynamics simulations with model chromosomes and crowders recapitulate the observed phenomena and highlight the role of entropic effects caused by confinement and molecular crowding in the spatial organization of the chromosome