Assessment of Elasticity and Topography of
            <i>Aspergillus nidulans</i>
            Spores via Atomic Force Microscopy

Zhao, Liming; Schaefer, David; Marten, Mark R.

doi:10.1128/aem.71.2.955-960.2005

Cited by 61 publications

(36 citation statements)

References 33 publications

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“…An important requirement for AFM investigations is that the sample be immobilized on a surface. For this purpose, an aliquot of bacterial suspension of ϳ10 5 cells per ml was allowed to adhere through electrostatic interactions to a very thin layer of poly-L-lysine on a glass substrate that was prepared as previously described (57). After 15 min, the bacterium-coated glass substrate was rinsed with deionized water to remove loosely attached bacteria and then transferred to the AFM for immediate measurement.…”

Section: Methodsmentioning

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: Methodsmentioning

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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“…Recently, atomic force microscopy (AFM) has emerged as a valuable tool that can be used not only to image the surface topography of a sample under physiological conditions but also to locally measure the mechanical properties of the material itself (15,28,34). To this end, force-indentation curves are commonly measured; these represent the relationship between the loading force and the depth of the indentation as the tip at the end of the AFM cantilever pushes onto the sample surface.…”

mentioning

confidence: 99%

Surface Viscoelasticity of Individual Gram-Negative Bacterial Cells Measured Using Atomic Force Microscopy

2008

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The cell envelope of gram-negative bacteria is responsible for many important biological functions: it plays a structural role, it accommodates the selective transfer of material across the cell wall, it undergoes changes made necessary by growth and division, and it transfers information about the environment into the cell. Thus, an accurate quantification of cell mechanical properties is required not only to understand physiological processes but also to help elucidate the relationship between cell surface structure and function. We have used a novel, atomic force microscopy (AFM)-based approach to probe the mechanical properties of single bacterial cells by applying a constant compressive force to the cell under fluid conditions while measuring the timedependent displacement (creep) of the AFM tip due to the viscoelastic properties of the cell. For these experiments, we chose a representative gram-negative bacterium, Pseudomonas aeruginosa PAO1, and we used regular V-shaped AFM cantilevers with pyramid-shaped and colloidal tips. We find that the cell response is well described by a three-element mechanical model which describes an effective cell spring constant, k 1 , and an effective time constant, , for the creep deformation. Adding glutaraldehyde, an agent that increases the covalent bonding of the cell surface, produced a significant increase in k 1 together with a significant decrease in . This work represents a new attempt toward the understanding of the nanomechanical properties of single bacteria while they are under fluid conditions, which could be of practical value for elucidating, for instance, the biomechanical effects of drugs (such as antibiotics) on pathogens.

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“…Digital image analysis systems run with powerful software packages that permit fully automated work and statistical evaluation of the measured data [10,11]. Recently, confocal laser scanning microscopy (CLSM) and fluorescence microscopy have been employed successfully in fungal morphology studies offering precise structural analysis of the mycelium and spores [12][13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Characterization of Fungal Morphology using Digital Image Analysis Techniques

Papagianni¹

2014

J Microb Biochem Technol

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The use of filamentous fungi for the production of commercially important products is old but keeps increasing during the last decades. New classes of compounds are being added in the list of products of fungal fermentations as a result of progress in methodologies and applications of biotechnology. Fungi are morphologically complex organisms that differ in structure throughout their life cycle. In submerged fermentation fungal morphology may take distinct forms ranging from dispersed filaments to densely interwoven masses of mycelium known as pellets. Each morphological form has each own characteristics that have a critical impact on the overall process outcome. Dispersed growth results in highly viscous broths with pseudoplastic behavior that have a negative impact on mass and energy transfer rates resulting in higher energy input requirements. Due to the high industrial relevance of fungal morphology there has been a substantial development of tools and techniques to characterize morphology and extract quantitative information that can be used in process control and optimization studies. Digital image analysis is the state of the art method to characterize and quantify fungal morphology in the developmental process from spores to filamentous structures to pellets. The progress made in the area since the 1990s, when the first image analysis methods were reported, is discussed in detail throughout the review.

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Assessment of Elasticity and Topography of Aspergillus nidulans Spores via Atomic Force Microscopy

Cited by 61 publications

References 33 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

Surface Viscoelasticity of Individual Gram-Negative Bacterial Cells Measured Using Atomic Force Microscopy

Characterization of Fungal Morphology using Digital Image Analysis Techniques

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