Comparison of the indentation and elasticity of E. coli and its spheroplasts by AFM

Sullivan, Claretta J.; Venkataraman, Sankar; Retterer, Scott T.; Allison, David P.; Doktycz, Mitchel J.

doi:10.1016/j.ultramic.2007.04.017

Cited by 34 publications

(31 citation statements)

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“…Mechanical perturbation of isolated sacculi studied using AFM later confirmed that this surface layer is flexible and elastic, springing back readily to its original position after the external pressure applied by the AFM tip was removed. Spheroplasts were found to be so easily deformed by the AFM tip that it has not been possible to estimate an effective spring constant for the wall-less cells, i.e., they appeared softer than the soft AFM cantilevers typically used for the study of cells (44). Therefore, the results of the present study, as well as the previous studies mentioned above, led us to suggest that the elastic response of the cells is largely dominated by the physical nature of the peptidoglycan network.…”

Section: Resultsmentioning

confidence: 99%

In Situ Characterization of Differences in the Viscoelastic Response of Individual Gram-Negative and Gram-Positive Bacterial Cells

2009

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We used a novel atomic force microscopy (AFM)-based technique to compare the local viscoelastic properties of individual gram-negative (Escherichia coli) and gram-positive (Bacillus subtilis) bacterial cells. We found that the viscoelastic properties of the bacterial cells are well described by a three-component mechanical model that combines an instantaneous elastic response and a delayed elastic response. These experiments have allowed us to investigate the relationship between the viscoelastic properties and the structure and composition of the cell envelope. In addition, this is the first report in which the mechanical role of Lpp, the major peptidoglycanassociated lipoprotein and one of the most abundant outer membrane proteins in E. coli cells, has been quantified. We expect that our findings will be helpful in increasing the understanding of the structureproperty relationships of bacterial cell envelopes.The surface layers that isolate the interior of a bacterial cell from its external environment play a crucial mechanical role in the survival of the cell. They must be strong enough to maintain the cellular shape and resist turgor pressure yet, at the same time, be flexible enough to allow cell growth and division. Their elastic response is evident from their ability to recover from transient deformations, such as those induced by the incorporation of additional surface components (e.g., proteins) in response to changes in environmental conditions and the passage of small molecules across the cell boundary. It is therefore clear that understanding many aspects of cell physiology requires knowledge of the mechanical properties of cells.The mechanical properties of the cell originate from the structural organization of the constituent lipids, sugar polymers, and proteins. Lipid molecules are brought together by their hydrophobic domains to form bilayers (membranes) that also incorporate different types of proteins. Polymeric strands of sugar molecules are typically cross-linked by flexible peptide molecules to form the peptidoglycan layer (27). Sometimes, an additional layer of proteins (S layer) is found on the outermost surface of the cell (7,8,40). Depending on the structural organization of the peptidoglycan and lipid bilayers, bacteria can generally be divided into gram-positive and gram-negative bacteria. In gram-positive cells, there is a relatively thick (20-to 35-nm) peptidoglycan layer that, together with the plasma membrane, sandwiches a viscous compartment called the periplasm (31, 32), whereas the envelope of gram-negative cells is made up of two lipid bilayers, the inner and outer membranes, separated by the periplasm, which contains a thin (3-to 8-nm) peptidoglycan layer (5, 33). In gram-negative bacteria, lipoproteins are associated with both the peptidoglycan layer and either the inner or outer membrane. Here, the "lipo" substituent is inserted into the hydrophobic domain of the membrane and the "protein" portion is linked to the peptidoglycan layer by either covalent or electrostatic bonds...

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Section: Resultsmentioning

confidence: 99%

In Situ Characterization of Differences in the Viscoelastic Response of Individual Gram-Negative and Gram-Positive Bacterial Cells

2009

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“…The SMD simulation also shows a supporting result, illustrating the deformation of the HRP active site of conformation under force pulling. In the literature, there are studies on enzyme folding and unfolding under the overall denature solutions, where the enzymes present either in the denatured condition with unfolded conformation or in the enzymatic reaction condition with fully folded conformation (46)(47)(48)(49). It is a challenge to study how the enzymatic conformation affects the enzymatic activity in the enzymatic physiological condition.…”

Section: Discussionmentioning

confidence: 99%

Interrogating the activities of conformational deformed enzyme by single-molecule fluorescence-magnetic tweezers microscopy

Guo

2015

Proc. Natl. Acad. Sci. U.S.A.

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Characterizing the impact of fluctuating enzyme conformation on enzymatic activity is critical in understanding the structure-function relationship and enzymatic reaction dynamics. Different from studying enzyme conformations under a denaturing condition, it is highly informative to manipulate the conformation of an enzyme under an enzymatic reaction condition while monitoring the real-time enzymatic activity changes simultaneously. By perturbing conformation of horseradish peroxidase (HRP) molecules using our home-developed single-molecule total internal reflection magnetic tweezers, we successfully manipulated the enzymatic conformation and probed the enzymatic activity changes of HRP in a catalyzed H 2 O 2-amplex red reaction. We also observed a significant tolerance of the enzyme activity to the enzyme conformational perturbation. Our results provide a further understanding of the relation between enzyme behavior and enzymatic conformational fluctuation, enzymesubstrate interactions, enzyme-substrate active complex formation, and protein folding-binding interactions.enzyme | single molecule TIRF-magnetic tweezers microscopy | manipulate the conformation | enzymatic conformational dynamics | conformational fluctuation

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“…Prior to coating with poly-L-lysine (P8920MW 150 to 300K; Sigma-Aldrich, Saint Louis, MO), silicon wafer disks were cleaned rigorously with 70% ethanol and DI water and dried on a hotplate at 30°C. A 200-l aliquot of 0.01% poly-L-lysine solution was dropped on the center of the silicon wafer disk, and the disks were placed on the 30°C hotplate for 10 min (15,48). Finally, DI water was used to gently rinse the silicon wafer surface to remove loosely bound poly-L-lysine molecules.…”

Section: Methodsmentioning

confidence: 99%

“…Generally, the force measurements within an AFM image were all completed by the same cantilever tip unless the reproducibility in force measurement became worse due to tip damage or contamination. The approach and retraction curves between the cantilever tip and the bare silicon wafer were always reproducible and thus easily averaged, whereas the approach and retraction curves on E. coli cells varied because of the complex heterogeneous bacterial surface; thus, these curves were analyzed individually as described previously (48,30,62). Finally, the reported force-distance curves were plotted with averaged data, and the probabilities of occurrence for the indentation and adhesion forces are also discussed below.…”

Section: Methodsmentioning

confidence: 99%

“…In contrast, atomic force microscopy (AFM) is attractive because microbial cells can be maintained and imaged in aqueous environments at nanometer spatial resolution. Meanwhile, AFM is capable of measuring piconewton forces in liquid, and the generated force-distance curves can be used to determine the hardness and elasticity (48) as well as the adhesiveness (53,62) of bacterial cells. Moreover, the electrical mode of AFM, known as Kelvin probe force microscopy (KPFM), can be used to map and quantify the local surface potential down to the resolution of the cantilever tip diameter (31,32).…”

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confidence: 99%

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Impacts of Hematite Nanoparticle Exposure on Biomechanical, Adhesive, and Surface Electrical Properties of Escherichia coli Cells

Zhang

Hughes

Chen

2012

Appl Environ Microbiol

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cDespite a wealth of studies examining the toxicity of engineered nanomaterials, current knowledge on their cytotoxic mechanisms (particularly from a physical perspective) remains limited. In this work, we imaged and quantitatively characterized the biomechanical (hardness and elasticity), adhesive, and surface electrical properties of Escherichia coli cells with and without exposure to hematite nanoparticles (NPs) in an effort to advance our understanding of the cytotoxic impacts of nanomaterials. Both scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that E. coli cells had noticeable deformation with hematite treatment for 45 min with a statistical significance. The hematite-treated cells became significantly harder or stiffer than untreated ones, as evidenced by indentation and spring constant measurements. The average indentation of the hematite-treated E. coli cells was 120 nm, which is significantly lower (P < 0.01) than that of the untreated cells (approximately 400 nm). The spring constant of hematite-treated E. coli cells (0.28 ؎ 0.11 nN/nm) was about 20 times higher than that of untreated ones (0.01 ؎ 0.01 nN/nm). The zeta potential of E. coli cells, measured by dynamic light scattering (DLS), was shown to shift from ؊4 ؎ 2 mV to ؊27 ؎ 8 mV with progressive surface adsorption of hematite NPs, a finding which is consistent with the local surface potential measured by Kelvin probe force microscopy (KPFM). Overall, the reported findings quantitatively revealed the adverse impacts of nanomaterial exposure on physical properties of bacterial cells and should provide insight into the toxicity mechanisms of nanomaterials.

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Comparison of the indentation and elasticity of E. coli and its spheroplasts by AFM

Cited by 34 publications

References 50 publications

In Situ Characterization of Differences in the Viscoelastic Response of Individual Gram-Negative and Gram-Positive Bacterial Cells

In Situ Characterization of Differences in the Viscoelastic Response of Individual Gram-Negative and Gram-Positive Bacterial Cells

Interrogating the activities of conformational deformed enzyme by single-molecule fluorescence-magnetic tweezers microscopy

Impacts of Hematite Nanoparticle Exposure on Biomechanical, Adhesive, and Surface Electrical Properties of Escherichia coli Cells

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