Ultrastructure of the surface film of bacterial colonies (original) (raw)
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Surface films of Escherichia coli colonies
FEMS Microbiology Letters, 1993
Escherichia coli colony surfaces were examined using SEM and TEM. The results indicated that bacterial colonies in the course of their development produce surface films which become thicker with increased growth duration. Membrane vesicles contribute to the formation of the surface film. The complex organization of the film suggests that it may perform specific functions.
Bacteria were first studied under the light microscope, using dyes and stains to investigate their structural features. Such methods showed that bacteria were of varying shapes and sizes. There was a cell wall, from which fla-gella could be observed to originate, a capsule surrounded the bacterial cell, a nuclear area was visible within the cytoplasm, and inclusion bodies were identified on the basis of their colour reaction with certain stains. Later, the use of phase-contrast light microscopy allowed living bacteria to be observed, but even under the best conditions it was not possible to study the ultrastructure, i.e. the fine structure, of bacteria. The advent of the electron microscope with its high resolving power changed all this and revolutionized the study of bacterial ultrastructure. The use of electron microscopes permitted new insights into bacterial organization, and these could now be linked to cellular functions. There have been many exciting developments not only in instrumentation [1] but also in the procedures used to prepare specimens for microscopy [2]. These have improved and greatly added to our knowledge of bacterial ultrastructure. It has emerged that the bacterial cell is a dynamic entity rather than a static one, and it is the aim of this chapter to highlight these new aspects of bacterial structural studies, and point the way for future investigations at a molecular level. GENERAL MORPHOLOGY Bacteria are small, prokaryotic cells, generally of the size of mitochondria. Their length varies from about 0.2 to more than 10 µm, and their width from about 0.2 to 1.5 µm. A variety of bacterial shapes can be observed under the light microscope, including cocci, rods, spiral, and even cubes! These shapes can also be observed by scanning electron microscopy (SEM), which provides both a three-dimensional view of cellular structures and information about their surface topography (Fig. 2.1). Apart from recording cell shape, SEM investigations can, for example, be coupled with studies on the effects of various drugs on overall morphology (Fig. 2.2a,b). External and internal bacterial structures can be investigated at high resolution by transmission electron microscopy (TEM). In a procedure known as negative staining, whole bacteria or isolated structures, such as pili, fimbriae, etc., are attached to metallic support grids covered with a very thin plastic film of collodion or for-mvar, or even with ultrathin sections (60 nm) of pure acrylic resin (LR White) and which provides the most stable support [3]. Then a heavy metal stain, such as uranyl acetate or phosphotungstic acid, is dried down over the preparation and details of surface structural features are revealed. Alternatively, a metal, usually platinum, can be vaporized within a vacuum coater, to cast a shadow over the specimen attached to a support grid, to highlight structural surface features. This is a procedure known as metal shadowing. In another popular procedure, bacterial preparations are embedded into a resin which, after hardening , can be cut into very thin sections or slices with an ultramicrotome. These ultrathin sections, less than 0.1 µm in thickness, can reveal the internal structure and organization of bacteria [4]. By these means electron microscopy reveals that bacteria have a variety of surface appendages such as fla-gella, pili/fimbriae, and slime or capsular layers that extend from the cell wall. The inner surface of the cell wall is in contact with a cytoplasmic membrane within which there is the cytoplasm. This contains a nuclear region of DNA, ribosomes and various inclusion bodies (Fig. 2.3). There are no unit membrane-bound structures, as are found in eukaryotic cells, but inclusion bodies such as carboxysomes, lipid bodies, and gas vacuoles, and the complex cell membrane systems of photosynthetic bacteria are surrounded by a non-unit protein layer. 7 Molecular Medical Microbiology.
Structures of two different surface layers found in six Bacteroides strains
Journal of Bacteriology, 1985
The structures of crystalline layers from six Bacteroides strains were studied by electron microscopy. Two different hexagonal crystalline surface layers were found, one with a unit cell spacing of 21.5 nm and another with a spacing of 7.7 nm. A three-dimensional structure of the 21.5-nm layer and a two-dimensional projection of the 7.7-nm layer were determined to 3.0- and 3.8-nm resolution, respectively, by computerized image processing of electron micrographs. Both of these two crystalline layers were found in all six strains studied: B. pentosaceus NP333T and WPH61, B. capillus ATCC 33690T and ATCC 33691, and B. buccae ATCC 33574T and ES57. This further supports the identity of B. pentosaceus, B. capillus, and B. buccae as suggested by M. Haapasalo, K. Lounatmaa, H. Ranta, H. Shah, and K. Ranta (Int. J. Syst. Bacteriol. 35:65-72, 1985). The surface layer with 21.5-nm spacing is an intricate network with two classes of pores through the layer.
Micron (1969), 1983
The general morphological features of the Gram-negative bacterium Pseudomonas avenae have been studied by electron microscopy. Electron micrographs from negatively stained specimens show the outermost surface layer to be composed of subunits arranged in a crystalline tetragonal array, with an average lattice spacing of 6.7 nm and unit cell of 9.7 nm when determined by image processing methods. Experiments designed to show the effects of various negative stains on the bacterial cell wall morphology suggest that the 'convoluted' or 'smooth' appearance ofthe wall material can be influenced by different stains when mixed with cells in liquid suspension.
OALib, 2015
The mechanism formation of colonies and biofilms of bacteria and yeasts are studied always of great interest. The aim of the presented work was transmission and scanning electron microscopic analysis contacts between cells of bacteria and yeast in biomofilms on natural structures and inorganic surface, as a result of formation of close contacts between a cellular wall, a fringe, crosspieces, symplasts and cells of Escherichia coli, Shigella flexnerii Salmonella of typhi, Salmonella typhimurium and also some probiotic lactic acid on nutritious agar surfaces. Intercellular contacts in yeast biomofilms on plates of zirconium were scanning electron microscopic visualized by Candida guilliermondii.
Role of Cell Surface Structures in Biofilm Formation by <i>Escherichia coli</i>
Food and Nutrition Sciences, 2015
This study aims to understand the relationship between capabilities of Escherichia coli strains to form biofilm and serotype groups expressed on cell surface. Sixteen strains of E. coli were originally isolated from different food processing lines in different Moroccan cities. Strains serotyped based on their O (somatic), H (flagellar), and K (capsular) surface antigen profiles using different antiserums. Biofilm assays carried out in 96-well microtiter dishes using the method of O'Toole et al. Our results show that no clear relation observed between origin and serotype groups. In the other hand, we observed that not all studied strains were able to form biofilm. Furthermore, combination of antigens H40 and K11 appears to be involved in biofilm formation. In fact, the H antigen seems to be implicated in the placement of the bacterial cells near the surface and the K antigen may play a role in physicochemical interactions between bacteria and inert surface.
Ultrastructure of colony-like communities of bacteria
APMIS, 1997
Colony-like communities are poorly studied forms of bacterial growth on agar. These communities are formed after the growth of large amounts of bacteria simultaneously plated onto a limited area of agar, while "classical" colonies are formed as a result of single bacterial cell multiplication. Colonylike communities of Gram-negative and Gram-positive bacteria differ from "classical" microbial colonies in their ultrastructural organization. Almost every cell in colony-like communities has an individual capsule-like envelope (glycocalyx). The cells in these communities are characterized by accelerated ageing. In the course of their development both bacterial colony-like communities and "classical" colonies produce a film, the basic part of which is represented by an elementary membrane. In contrast to "classical" colonies, the thickness of the amorphous layers of this film in colony-like communities did not significantly increase after 24 h of cultivation. The formation of a three-dimensional network of cells in colony-like communities is similar to this process in "classical" colonies. The intercellular matrix of colony-like communities contains numerous membrane vesicles, and has a more amorphous structure and higher electron density than that of "classical" bacterial colonies.
Ultrastructure of Resting Cells of Some Non-Spore-Forming Bacteria
Microbiology, 2004
Using electron microscopy (ultrathin sections and freeze-fractures), we investigated the ultrastructure of the resting cells formed in cultures of Micrococcus luteus, Arthrobacter globiformis , and Pseudomonas aurantiaca under conditions of prolonged incubation (up to 9 months). These resting cells included cystlike forms that were characterized by a complex cell structure and the following ultrastructural properties: (i) a thickened or multiprofiled cell wall (CW), typically made up of a layer of the preexisting CW and one to three de novo synthesized murein layers; (ii) a thick, structurally differentiated capsule; (iii) the presence of large intramembrane particles (d = 180-270 Å), occurring both on the PF and EF faces of the membrane fractures of M. luteus and A. globiformis ; (iv) a peculiar structure of the cytoplasm, which was either fine-grained or lumpy (coarse-grained) in different parts of the cell population; and (v) a condensed nucleoid. Intense formation of cystlike cells occurred in aged (2-to 9-month-old) bacterial cultures grown on diluted complex media or on nitrogen-, carbon-, and phosphorus-limited synthetic media, as well as in cell suspensions incubated in media with sodium silicate. The general morphological properties, ultrastructural organization, and physiological features of cystlike cells formed during the developmental cycle suggest that constitutive dormancy is characteristic of non-spore-forming bacteria.
Surface Proteins on Gram-Positive Bacteria
Microbiology spectrum, 2019
As arms, legs, hair, and fur are used in higher species for their survival in the environment, surface appendages are used by bacteria for similar purposes. Surface molecules in bacteria range from complex structures such as flagella that propel the organism in aqueous environments, to less sophisticated polysaccharides and proteins. All of these molecules serve to benefit the organism for survival in a hostile environment, such as the waters of a rushing stream, the blood of an infected animal, the surface of an object, or the surface of a mucosal epithelium. Although it was previously believed that bacteria were simple single-cell organisms with little complexity, it is now apparent that they are highly evolved, advanced particles that possess a wide array of surface molecules that serve to manipulate the organism in its environment. For human pathogens, surface molecules have been finely tuned to allow adherence and colonization of host surfaces, invasion of cells, evasion of the host's immune response, and persistence in infected tissues. In an effort to emphasize the complexity of bacterial surface molecules and their use in the everyday life of the bacterium, this chapter will focus on those surface proteins found on grampositive bacteria. For an extensive review of the subject, see references (1, 2). GRAM-POSITIVE CELL WALL From electron microscopic analysis of the gram-positive cell envelope (see chapter 1, this volume) and a number of elegant chemical, structural and immunological analyses, a picture of the gram-positive cell wall has emerged (Fig. 1). The structure differs significantly from the gram-negative cell wall in two ways: (i) the presence of a thicker and more cross-linked peptidoglycan and (ii) the lack of an outer membrane. Because of these differences, surface molecules on gram-positive organisms vary from those on gram-negative organisms, requiring specialized systems to transport and anchor molecules through the outer membrane(3, 4). In general, surface proteins in gram-positive bacteria can be separated into three categories: (i) those that anchor at their C-terminal ends (through an LPxTG motif), (ii) those that bind by way of charge or hydrophobic interactions, and (iii) those that bind via their N-terminal region (lipoproteins) (Fig. 1).