näkemys - Computational Biology - # Evolutionary rescue of fitness-compromised bacterial mutants lacking the cell shape protein MreB

Experimental Evolution Restores Cell Size Homeostasis in Bacteria Lacking the Cell Shape Determinant MreB

Q: How might the insights from this study on cell size homeostasis in bacteria be applied to understanding cell size regulation in other organisms, such as eukaryotic cells

The insights gained from this study on cell size homeostasis in bacteria can provide valuable information for understanding cell size regulation in other organisms, including eukaryotic cells. While bacteria and eukaryotic cells have distinct structural and organizational differences, there are fundamental principles of cell size control that are likely conserved across different domains of life. One key aspect that can be applied to eukaryotic cells is the concept of cell volume homeostasis. The mechanisms that govern cell size maintenance and the balance between cell growth and division are crucial for the overall health and function of cells. By studying how bacteria regulate their cell size in response to genetic perturbations, such as the loss of MreB, researchers can gain insights into the molecular pathways and processes that contribute to cell size regulation in eukaryotic cells. Understanding the interplay between cell wall synthesis, membrane tension, and turgor pressure in bacterial cells can provide a framework for investigating similar mechanisms in eukaryotic cells, where processes like cytoskeletal dynamics, membrane trafficking, and cell cycle regulation play key roles in determining cell size. Additionally, the identification of specific genetic mutations, such as those in Pbp1A, that can compensate for the loss of MreB and restore fitness in bacteria can shed light on potential genetic regulators of cell size in eukaryotic cells. By studying the functional consequences of these mutations and their impact on cell morphology and growth dynamics, researchers can uncover novel pathways and molecular players involved in cell size control across different organisms.

Q: What other cellular processes or pathways might be involved in compensating for the loss of MreB and restoring fitness in the ΔmreB mutant, beyond the mutations identified in Pbp1A and the Δpflu4921-4925 deletion

In addition to the mutations identified in Pbp1A and the Δpflu4921-4925 deletion, there are likely other cellular processes and pathways involved in compensating for the loss of MreB and restoring fitness in the ΔmreB mutant. Some potential mechanisms that could contribute to this compensatory response include: Cell Wall Remodeling: Apart from Pbp1A, other components of the cell wall synthesis machinery may undergo changes to adapt to the absence of MreB. This could involve alterations in the activity or expression of other penicillin-binding proteins (PBPs) or enzymes involved in peptidoglycan synthesis. Cytoskeletal Rearrangements: Loss of MreB, an actin-like protein, could trigger compensatory changes in the bacterial cytoskeleton. This may involve the reorganization of other cytoskeletal elements, such as FtsZ or MreC/D, to maintain cell shape and division. Metabolic Adaptations: The loss of MreB could impact cellular metabolism and energy utilization. Compensatory mutations or changes in metabolic pathways may help the bacteria cope with the altered cell shape and maintain essential cellular functions. Stress Response Pathways: The absence of MreB could induce stress responses in the cell. Activation of stress response pathways, such as the sigma factor regulon or heat shock proteins, may play a role in restoring cellular homeostasis and fitness. Cell Division Machinery: Changes in the regulation of cell division proteins and processes, such as the divisome components or septum formation, could contribute to the restoration of fitness in the ΔmreB mutant. By exploring these and other potential mechanisms, researchers can gain a more comprehensive understanding of the complex cellular adaptations that occur in response to genetic perturbations and the strategies cells employ to maintain fitness and survival.

Keskeiset käsitteet

Deletion of the cell shape determinant MreB in Pseudomonas fluorescens SBW25 results in viable spherical cells with reduced fitness, which can be rapidly restored through compensatory mutations in the peptidoglycan synthesis protein Pbp1A that enhance cell size homeostasis.

Tiivistelmä

The study investigates the evolutionary rescue of a Pseudomonas fluorescens SBW25 mutant lacking the cell shape determinant MreB. Deletion of mreB results in viable spherical cells with variable volume and reduced fitness compared to the ancestral rod-shaped cells.

A 1,000-generation selection experiment was conducted, which led to rapid restoration of fitness in the derived lines. Whole-genome sequencing identified mutations in the peptidoglycan synthesis protein Pbp1A as the main route for fitness restoration. Genetic reconstructions demonstrated that Pbp1A mutations targeting the transpeptidase activity enhance homogeneity in cell wall synthesis on lateral surfaces, thus restoring cell size homeostasis in the population.

The study shows that the reduced fitness of the ΔmreB mutant is primarily due to the production of non-viable cells with variable volume, caused by asymmetric cell division and imprecise septum positioning. The evolved Pbp1A mutations compensate for this by improving the fidelity of cell division and restoring the balance between cell elongation and septation rates, thereby maintaining cell volume homeostasis.

In contrast, a five-gene deletion (Δpflu4921-4925) identified in one of the evolved lines was also able to restore fitness in the ΔmreB background, but did not fully recapitulate the cell size homeostasis phenotype observed with the Pbp1A mutations. The study emphasizes the power of experimental evolution in uncovering new insights into the molecular determinants of complex phenotypes like cell shape and size control.

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Tilastot

The ΔmreB mutant had a relative fitness of 0.77 compared to the ancestral SBW25 strain.
The average cell volume of the ΔmreB mutant was 20.65 ± 16.17 μm³, compared to 3.27 ± 0.94 μm³ for ancestral SBW25 cells.
The proportion of viable ΔmreB cells was 81%, compared to 95% for ancestral SBW25.
The relative difference in elongation rate between sister ΔmreB cells was 55%, compared to 5% in ancestral SBW25.
The relative difference in cell volume between daughter ΔmreB cells was 19.4%, compared to 5% in ancestral SBW25.

Lainaukset

"Deletion of mreB from Pseudomonas fluorescens SBW25 results in viable spherical cells of variable volume and reduced fitness."
"Mutations in the peptidoglycan synthesis protein Pbp1A were identified as the main route for fitness restoration with genetic reconstructions demonstrating causality."
"The pbp1A mutations targeting transpeptidase activity enhance homogeneity in cell wall synthesis on lateral surfaces, thus restoring cell size homeostasis in the population."

Tärkeimmät oivallukset

Evolutionary rescue of spherical mreB deletion mutants of the rod-shape bacterium Pseudomonas fluorescens SBW25

by Yulo,P. R., ... klo www.biorxiv.org 02-11-2018

https://www.biorxiv.org/content/10.1101/263681v3

Syvällisempiä Kysymyksiä

How might the insights from this study on cell size homeostasis in bacteria be applied to understanding cell size regulation in other organisms, such as eukaryotic cells

The insights gained from this study on cell size homeostasis in bacteria can provide valuable information for understanding cell size regulation in other organisms, including eukaryotic cells. While bacteria and eukaryotic cells have distinct structural and organizational differences, there are fundamental principles of cell size control that are likely conserved across different domains of life.
One key aspect that can be applied to eukaryotic cells is the concept of cell volume homeostasis. The mechanisms that govern cell size maintenance and the balance between cell growth and division are crucial for the overall health and function of cells. By studying how bacteria regulate their cell size in response to genetic perturbations, such as the loss of MreB, researchers can gain insights into the molecular pathways and processes that contribute to cell size regulation in eukaryotic cells. Understanding the interplay between cell wall synthesis, membrane tension, and turgor pressure in bacterial cells can provide a framework for investigating similar mechanisms in eukaryotic cells, where processes like cytoskeletal dynamics, membrane trafficking, and cell cycle regulation play key roles in determining cell size.
Additionally, the identification of specific genetic mutations, such as those in Pbp1A, that can compensate for the loss of MreB and restore fitness in bacteria can shed light on potential genetic regulators of cell size in eukaryotic cells. By studying the functional consequences of these mutations and their impact on cell morphology and growth dynamics, researchers can uncover novel pathways and molecular players involved in cell size control across different organisms.

What other cellular processes or pathways might be involved in compensating for the loss of MreB and restoring fitness in the ΔmreB mutant, beyond the mutations identified in Pbp1A and the Δpflu4921-4925 deletion

In addition to the mutations identified in Pbp1A and the Δpflu4921-4925 deletion, there are likely other cellular processes and pathways involved in compensating for the loss of MreB and restoring fitness in the ΔmreB mutant. Some potential mechanisms that could contribute to this compensatory response include:

Cell Wall Remodeling: Apart from Pbp1A, other components of the cell wall synthesis machinery may undergo changes to adapt to the absence of MreB. This could involve alterations in the activity or expression of other penicillin-binding proteins (PBPs) or enzymes involved in peptidoglycan synthesis.

Cytoskeletal Rearrangements: Loss of MreB, an actin-like protein, could trigger compensatory changes in the bacterial cytoskeleton. This may involve the reorganization of other cytoskeletal elements, such as FtsZ or MreC/D, to maintain cell shape and division.

Metabolic Adaptations: The loss of MreB could impact cellular metabolism and energy utilization. Compensatory mutations or changes in metabolic pathways may help the bacteria cope with the altered cell shape and maintain essential cellular functions.

Stress Response Pathways: The absence of MreB could induce stress responses in the cell. Activation of stress response pathways, such as the sigma factor regulon or heat shock proteins, may play a role in restoring cellular homeostasis and fitness.

Cell Division Machinery: Changes in the regulation of cell division proteins and processes, such as the divisome components or septum formation, could contribute to the restoration of fitness in the ΔmreB mutant.

By exploring these and other potential mechanisms, researchers can gain a more comprehensive understanding of the complex cellular adaptations that occur in response to genetic perturbations and the strategies cells employ to maintain fitness and survival.

Could the experimental evolution approach used in this study be applied to investigate the evolutionary dynamics and genetic basis of other complex bacterial phenotypes, such as antibiotic resistance or virulence

The experimental evolution approach used in this study to investigate the evolutionary dynamics and genetic basis of cell shape restoration in the ΔmreB mutant could be applied to study other complex bacterial phenotypes, such as antibiotic resistance or virulence. By subjecting bacterial populations to selective pressures and monitoring their adaptation over multiple generations, researchers can uncover the genetic changes and evolutionary trajectories that lead to the emergence of antibiotic resistance or altered virulence phenotypes.
For studying antibiotic resistance:

Selection Experiments: Researchers can expose bacterial populations to sublethal concentrations of antibiotics and track the evolution of resistance over time. By sequencing the genomes of evolved strains, novel resistance mechanisms and genetic mutations conferring resistance can be identified.

Fitness Trade-offs: Investigating the fitness costs associated with antibiotic resistance mutations and the compensatory mutations that restore fitness can provide insights into the genetic basis of resistance and the potential pathways for overcoming resistance.

Parallel Evolution: Studying multiple replicate populations under the same selective pressure can reveal common genetic changes that arise independently, highlighting key genetic targets for resistance.

For studying virulence:

Host-Pathogen Interactions: Experimental evolution studies can be designed to mimic host-pathogen interactions and explore how bacterial pathogens evolve to enhance their virulence or evade host immune responses.

Pathway Analysis: By integrating genomic data with functional assays and phenotypic characterization, researchers can identify the genetic pathways and regulatory networks involved in virulence modulation.

Comparative Genomics: Comparative genomics of evolved strains with varying virulence phenotypes can uncover genetic signatures associated with increased pathogenicity and provide insights into the evolutionary mechanisms driving virulence evolution.

Overall, the experimental evolution approach offers a powerful tool for studying the genetic basis of complex bacterial phenotypes and understanding the dynamics of adaptation in response to selective pressures.