Physical basis for the adaptive flexibility of
            <i>Bacillus</i>
            spore coats

Şahin, Özgür; Yong, Ee Hou; Driks, Adam; Mahadevan, L.

doi:10.1098/rsif.2012.0470

Cited by 39 publications

(33 citation statements)

References 32 publications

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“…For example, dormant spores of Bacillus thuringiensis expand and shrink in response to increasing and decreasing relative humidity on different time scales from tens of seconds to minutes (45). The contraction of the coat often is accompanied by the formation of small ridges on the spore surface (46). showed that the surface of Bacillus thuringiensis is covered with crystalline hexagonal honeycomb structures; the surface of Bacillus cereus spores is covered with small randomly oriented domains.…”

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Nanomechanical Characterization of Bacillus anthracis Spores by Atomic Force Microscopy

Burggraf

Xing

2016

Appl Environ Microbiol

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The study of structures and properties of bacterial spores is important to understanding spore formation and biological responses to environmental stresses. While significant progress has been made over the years in elucidating the multilayer architecture of spores, the mechanical properties of the spore interior are not known. Here, we present a thermal atomic force microscopy (AFM) study of the nanomechanical properties of internal structures of Bacillus anthracis spores. We developed a nanosurgical sectioning method in which a stiff diamond AFM tip was used to cut an individual spore, exposing its internal structure, and a soft AFM tip was used to image and characterize the spore interior on the nanometer scale. We observed that the elastic modulus and adhesion force, including their thermal responses at elevated temperatures, varied significantly in different regions of the spore section. Our AFM images indicated that the peptidoglycan (PG) cortex of Bacillus anthracis spores consisted of rod-like nanometer-sized structures that are oriented in the direction perpendicular to the spore surface. Our findings may shed light on the spore architecture and properties. IMPORTANCEA nanosurgical AFM method was developed that can be used to probe the structure and properties of the spore interior. The previously unknown ultrastructure of the PG cortex of Bacillus anthracis spores was observed to consist of nanometer-sized rodlike structures that are oriented in the direction perpendicular to the spore surface. The variations in the nanomechanical properties of the spore section were largely correlated with its chemical composition. Different components of the spore materials showed different thermal responses at elevated temperatures. Structures and material properties of bacterial spores play an important role in protecting them against a variety of environmental stresses, such as toxic chemicals (1), radiation (2, 3), and heat (3-5). The current knowledge of spore structures has been obtained largely using transmission electron microscopy (TEM) methods in various forms (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). A mature spore usually shows a concentric multilayer structure, consisting of the core, inner membrane, germ cell wall, cortex, outer membrane, and coat assembly. For Bacillus anthracis spores, there is an exosporium layer that loosely encases the spore. The spore core, which contains mostly DNA, RNA, enzymes, and dipicolinic acid (DPA), is in a dehydrated and metabolically dormant state (21-25). The ability of bacterial spores to survive for long durations, sometimes in harsh environments, has been attributed to the immobilization of essential DNA, RNA, and enzymes by small, acid-soluble spore proteins (SASP) (28-30). It was suggested that the DPA can be intercalated with spore DNA and RNA through covalent bonds, forming a gel-like polymer matrix (26,27). It is worth mentioning that the DPA structure in the spore core is not well understood. The germ cell wall (e.g., inner cortex) and ...

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confidence: 99%

Nanomechanical Characterization of Bacillus anthracis Spores by Atomic Force Microscopy

Burggraf

Xing

2016

Appl Environ Microbiol

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“…This, in turn, allows a major influx of water into the core, thereby causing it to swell and to rehydrate sufficiently to support metabolism. Concomitantly, the coat (as well as any of the other, more exotic outer layers that are present in many species [5]) is shed by processes that remain poorly understood (7). Disassembly of these layers reveals the germ cell wall, which serves as the cell wall of a newly emerging vegetative cell.…”

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Protein Synthesis during Germination: Shedding New Light on a Classical Question

Boone

Driks

2016

J Bacteriol

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Bacterial spores were discovered by Cohn and Koch in the species Bacillus subtilis and Bacillus anthracis and described in two jointly published papers in the year 1876 (1). Among the most striking of their observations was that spores are metabolically dormant and highly resistant. In spite of these features, however, spores can break dormancy extremely rapidly; within minutes of sensing the appropriate stimulus (typically, a small molecule such as an amino acid or a sugar) the spore converts to a vegetative cell and resumes growth and division (2). During the first step in this revival process, known as germination, the dormant spore sheds its protective outer layers, takes up water, and swells. In the second step, called outgrowth, the spore begins active production of new cellular macromolecules. Outgrowth is complete when the cell fully converts to a rod shape; the now fully restored vegetative cell is poised to begin division. This rapid reawakening from the dead (or the near dead) raises a number of intriguing and very deep questions, including (i) how can metabolism be reactivated so quickly after the completion of germination and (ii) do spores really lack all metabolic activity? Or, to phrase it another way, just how dead are spores, anyway?Elucidating the mechanistic basis of germination and outgrowth is one of the longest-running challenges in microbiology; despite nearly 150 years of research, there are still major gaps in our understanding of these processes. Nonetheless, since germination was first observed, a large body of evidence has accumulated documenting that, throughout the course of germination, up until the start of outgrowth, spores are, indeed, quite dormant; no metabolic or biosynthetic processes (until quite recently) have been detected. While these data appeared to exclude significant levels of metabolic activity during germination, an outstanding question has always lingered: could germinating spores possess some degree of physiologically important metabolic activity that is simply too low to detect or for some other reason inaccessible to measurement by the methods used so far?This issue was addressed in a landmark study in 2015 by Sinai et al. (3). These authors showed, first, that protein synthesis occurs prior to the completion of germination in two ways: (i) by a novel biochemical approach (bio-orthogonal noncanonical amino acid tagging [BONCAT]) that specifically identifies newly synthesized proteins and (ii) by monitoring the timing, during germination, of the appearance of fluorescently tagged versions of some of the proteins discovered by BONCAT. Second, and more directly relevant to our discussion here, these authors argued that protein synthesis is required for successful germination by demonstrating that (i) protein synthesis inhibitors (specifically, the antibiotics tetracycline and lincomycin) prevent germination (cleverly overcoming the limitations of previous experiments attempting to use antibiotics in a similar manner, by increasing spore permeability during antib...

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“…However, it is certainly possible that there are changes in the coat associated with germination that facilitate the swelling of spores' outer layers in response to core swelling, and there is a recent report consistent with this idea (29). In addition, whole dormant spores can swell and contract significantly in both the major and minor axes, and this has been suggested to be due at least in part to changes in spore core water content (29,30). It should be noted that the threshold value for ellipse fitting is normalized to 50% of the maximum image intensity that is reduced during germination.…”

Section: Discussionmentioning

confidence: 99%

“…We cannot answer this definitively at present, but it seems most likely that at a minimum it is core swelling that drives this process, since loss of significant amounts of the spore coat by mutation of the major assembly protein CotE has no significant effect on spore wet heat resistance, which is primarily dependent on the core water content (27,28). However, it is certainly possible that there are changes in the coat associated with germination that facilitate the swelling of spores' outer layers in response to core swelling, and there is a recent report consistent with this idea (29). In addition, whole dormant spores can swell and contract significantly in both the major and minor axes, and this has been suggested to be due at least in part to changes in spore core water content (29,30).…”

Section: Discussionmentioning

confidence: 99%

High-Precision Fitting Measurements of the Kinetics of Size Changes during Germination of Individual Bacillus Spores

Liang

Zhang

Setlow

et al. 2014

Appl Environ Microbiol

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bHigh-precision measurements of size changes of individual bacterial spores based on ellipse fitting to bright-field images recorded with a digital camera were employed to monitor the germination of Bacillus spores with a precision of ϳ5 nm. To characterize the germination of individual spores, we recorded bright-field and phase-contrast images and found that the timing of changes in their normalized intensities coincided, so the bright-field images can be used to characterize spore size and refractility changes during germination. The major conclusions from this work were as follows.

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Physical basis for the adaptive flexibility of Bacillus spore coats

Cited by 39 publications

References 32 publications

Nanomechanical Characterization of Bacillus anthracis Spores by Atomic Force Microscopy

Nanomechanical Characterization of Bacillus anthracis Spores by Atomic Force Microscopy

Protein Synthesis during Germination: Shedding New Light on a Classical Question

High-Precision Fitting Measurements of the Kinetics of Size Changes during Germination of Individual Bacillus Spores

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