Bacteria
Bacteria are single-celled microorganisms that can be found in various environments, including soil, water, and living organisms. They have diverse shapes and sizes and can be beneficial, such as aiding in digestion and nutrient cycling, or harmful, causing diseases. Bacteria play a crucial role in ecosystems and have significant impacts on human health and industry.
7 Key excerpts on "Bacteria"
eBook - ePubThe New Microbiology
From Microbiomes to CRISPR
- Pascale Cossart(Author)
- 2018(Publication Date)
- ASM Press(Publisher)
...PART I New Concepts in Microbiology CHAPTER 1 Bacteria: Many Friends, Few Enemies Bacteria are unicellular living organisms that make up one of the three domains of life: Bacteria, Archaea, and Eukaryota (Fig. 1). This model of three branches stemming from a common ancestor was first proposed by Carl Wo-ese in 1977. The absence of a nucleus is one major difference between prokaryotes and eukaryotes. Eukaryota or eukaryotes include animals, plants, fungi, and protozoa, which all have nuclei; Bacteria and archaea are prokaryotes and do not have a nucleus. The DNA of prokaryotes is non-membrane bound, unlike in eukaryotes. But do not assume that Bacteria are merely small sacks full of disorderly contents. Their “interior” is in fact very well organized. Archaea, like Bacteria, are unicellular organisms but differ from Bacteria in that they have lipids that are not found in Bacteria and an ensemble of compounds that are similar to those of eukaryotes, in particular the machinery that regulates gene expression. When they were discovered, archaea were thought to exist only in extreme environments, such as very hot water springs, but we now know that they are present everywhere, including in our gut. Figure 1. The three large domains of life. Bacteria, Archaea, and Eukaryota have a common ancestor. Bacteria are extremely varied and make up the most diverse domain of life. They have been on Earth for billions of years and have evolved to survive in a great variety of conditions. There are more than 11,500 known species of Bacteria in more than 2,000 genera (groupings of species). These numbers have so far been based only on gene comparisons, particularly the 16S RNA genes, and they keep rising. Classification methods are changing too. Now that we can compare entire genome sequences, the definition of “species” itself is evolving. Bacteria may have different shapes (Fig. 2)...
eBook - ePub- Simon Baker, Jane Nicklin, Caroline Griffiths(Authors)
- 2011(Publication Date)
- Taylor & Francis(Publisher)
...SECTION A – THE MICROBIAL WORLD A1 The microbial world Key Note Microorganisms are found in all three major kingdoms of life: the Bacteria, the Archaea, and the Eukarya. The presence of a nucleus defines the eukaryotes, while both the Bacteria and Archaea can be defined as prokaryotes. Apart from the nucleus, there are many physiological and biochemical properties distinguishing the prokaryotes from the eukaryotes. What are microbes? Microbes are a diverse group of organisms that can be divided into the viruses, unicellular groups (Archaea, EuBacteria, protista, some fungi, and some chlorophyta), and a small number of organisms with a simple multicellular structure (the larger fungi and chlorophyta). These larger microorganisms are characterized by having a filamentous, sheet-like or parenchymous thallus that does not display true tissue differentiation. Most microbes cannot be seen without the aid of a microscope. Microbiology Microbiology is defined as the study of microorganisms. The discipline now includes their molecular biology and functional ecology as well as the traditional studies of structure and physiology. The discipline began in the late 17th century with Leeuwenhoek's discovery of Bacteria using simple microscopy of mixed natural cultures...
eBook - ePub- David P. Clark(Author)
- 2009(Publication Date)
- Academic Cell(Publisher)
...They are also responsible for internal abscesses and most types of acute suppurative infection. Magnification: ×24,000. Provided by Dr Kari Lounatmaa, Science Photo Library. A smaller cell has a larger surface-to-volume ratio. Smaller cells transport nutrients relatively faster, per unit mass of cytoplasm (i.e., cell contents), and so can grow more rapidly than larger cells. Because Bacteria are less structurally complex than animals and plants, they are often referred to as “lower organisms.” However, it is important to remember that present-day Bacteria are at least as well adapted to modern conditions as animals and plants, and are just as highly evolved as so-called “higher organisms.” In many ways, Bacteria are not so much “primitive” as specialized for growing more efficiently in many environments than larger and more complex organisms. chromosome Structure containing the genes of a cell and made of a single molecule of DNA Escherichia coli A bacterium commonly used in molecular biology EuBacteria and ArchaeBacteria Are Genetically Distinct There are two distinct types of prokaryotes, the euBacteria and archaeBacteria, which are no more genetically related to each other than either group is to the eukaryotes. Both euBacteria and archaeBacteria show the typical prokaryotic structure—in other words, they both lack a nucleus and other internal membranes. Thus, cell structure is of little use for distinguishing these two groups. The euBacteria include most well known Bacteria, including all those that cause disease. When first discovered, the archaeBacteria were regarded as strange and primitive. This was largely because most are found in extreme environments (Fig. 2.09) and/or possessed unusual metabolic pathways. Some grow at very high temperatures, others in very acidic conditions and others in very high salt. The only major group of archaeBacteria found under “normal” conditions are the methane Bacteria, which, however, have a very strange metabolism...
eBook - ePub- Stuart Hogg(Author)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
...The Archaea are quite distinct from the true Bacteria and are thought to have diverged from a common ancestral line at a very early stage, before the evolution of eukaryotic organisms. The scheme illustrated is the one most widely accepted by microbiologists, but alternative models have been proposed. 3.1 The prokaryotic cell Bacteria are much smaller than eukaryotic cells; most fall into a size range of about 1–5 μm, although some may be larger than this. Some of the smallest Bacteria, such as the Mollicutes (mycoplasmas), measure less than 1 μm, and are too small to be resolved clearly by an ordinary light microscope. Because of their extremely small size, it was only with the advent of the electron microscope that we were able to learn about the detailed structure of Bacterial cells. Using the light microscope, however, it is possible to recognise differences in the shape and arrangement of Bacteria. Although a good deal of variation is possible, most have one of three basic shapes (Figure 3.2): In recent years, square, triangular and star-shaped Bacteria have all been discovered! rod-shaped (bacillus; pl. bacilli); spherical (coccus; pl. cocci); curved: these range from comma-shaped (vibrio) to corkscrew - shaped (spirochaete). Figure 3.2 Bacterial shapes. Most Bacteria are (a) rod-shaped, (b) spherical or (c) curved. These basic shapes may join to form (d) pairs, (e and f) chains, (g) sheets, (h) packets and (i) irregular aggregates. All these shapes confer certain advantages to their owners; rods, with a large surface area, are better able to take up nutrients from the environment, while the cocci are less prone to drying out. The spiral forms are usually motile; their shape aids their movement through an aqueous medium. As well as these characteristic cell shapes, Bacteria may also be found grouped together in particular formations...
eBook - ePub- Britannica Educational Publishing, Kara Rogers(Authors)
- 2010(Publication Date)
- Britannica Educational Publishing(Publisher)
...Biofilms can cause severe infections in hospitalized patients; the formation of biofilms in these instances is typically associated with the introduction into the body of foreign substrates, such as artificial implants and urinary catheters. Biofilms also form on the thin films of plaque found on teeth, where they ferment sugars and starches into acids, causing the destruction of tooth enamel. In the environment, biofilms fill an important role in the breakdown of organic wastes by filtering wastes from water and by removing or neutralizing contaminants in soil. As a result, biofilms are used to purify water in water treatment plants and to detoxify contaminated areas of the environment. DISTRIBUTION IN NATURE Prokaryotes are ubiquitous on the Earth’s surface. They are found in every accessible environment, from polar ice to bubbling hot springs, from mountaintops to the ocean floor, and from plant and animal bodies to forest soils. Some Bacteria can grow in soil or water at temperatures near freezing (0 °C [32 °F]), whereas others thrive in water at temperatures near boiling (100 °C [212 °F]). Each bacterium is adapted to live in a particular environmental niche, be it oceanic surfaces, mud sediments, soil, or the surfaces of another organism. The level of Bacteria in the air is low but significant, especially when dust has been suspended. In uncontaminated natural bodies of water, Bacterial counts can be in the thousands per millilitre; in fertile soil, Bacterial counts can be in the millions per gram; and in feces, Bacterial counts can exceed billions per gram. Prokaryotes are important members of their habitats. Although they are small in size, their sheer numbers mean that their metabolism plays an enormous role—sometimes beneficial, sometimes harmful—in the conversion of elements in their external environment...
eBook - ePubHandbook of Microbiology
Condensed Edition
- Allen I Laskin(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...Introduction to the Bacteria DR. HUBERT LECHEVALIER Bacteria are procaryotic organisms that, if photosynthetic, do not produce oxygen. Most Bacteria are quite small, being rods; cocci or filaments that range from 0.5 to 1 μm in diameter. Since the resolution of the light microscope is of the order of 0.2 to 0.3 μm, it is easily understandable that no great progress was made in the cytology of Bacteria before the introduction of the electron microscope and the development of allied methods of shadowing, thin-sectioning and staining. 1 - 3 The following diagram is an attempt at schematically illustrating the various cytological features that can be recognized in Bacteria. Of course, no single bacterium harbors all the features illustrated. Actual micrographs of most morphological features illustrated in the diagram can be found in the Pictorial Atlas of Pathogenic Microorganisms, edited by G. Henneberg 4 There is no rational order for presenting Bacteria. Thus, the order that we have chosen is entirely empirical; the section starts with autotrophic Bacteria and ends with heterotrophic rods and cocci not covered under other subdivisions. References 1. Hayat, M. A., Principles and Techniques of Electron Microscopy: Biological Applications, Vol. 1. Van Nostrand Reinhold Co., New York (1970). 2. Dawes, C. J., Biological Techniques in Electron Microscopy. Barnes & Noble, Inc., New York (1971). 3. Kay, D. H., Techniques for Electron Microscopy, 2nd ed. F. A. Davis Co., Philadelphia, Pennsylvania (1965). 4. Henneberg, G., Pictorial Atlas of Pathogenic Microorganisms, Vol. 3. Gustav Fischer Verlag, Stuttgart, Germany (1969)....
eBook - ePubTaxonomic Guide to Infectious Diseases
Understanding the Biologic Classes of Pathogenic Organisms
- Jules J. Berman(Author)
- 2019(Publication Date)
- Academic Press(Publisher)
...Three major groups of organisms account for all life on earth: Bacteria, archaea, and eukaryotes. When you compare species of Class Bacteria with species of Class Archaea, you're not likely to notice any big differences. The Bacteria have the same shapes and sizes as the archaea. All species of Bacteria and all species of archaea are single-celled organisms, and they all have a typical prokaryotic structure (i.e., lacking a membrane-bound nucleus to compartmentalize their genetic material). As it happens, Class Bacteria contains all of the prokaryotic organisms (i.e., cellular organisms lacking a nucleus) that are known to be pathogenic to humans. The archaeans are nonpathogenic; many are extremophiles, capable of living in hostile environments (e.g., hot springs, salt lakes), but some archaean species can occupy less demanding biological niches (e.g., marshland, soil, human colon). Class Archaea does not hold a monopoly on extremophilic prokaryotes; some members of Class Bacteria live in extreme environments (e.g., the alkaliphilic Bacillus halodurans). The third major class of organisms, the Eukaryotes, is distinguished by the presence of a membrane-bound nucleus. For decades, archaean species were considered just another class of Bacteria. This changed in 1977. Woese and Fox had been studying ribosomal RNA. Because ribosomal RNA is a fundamental constituent of all cellular organisms, sequence comparisons in the genes coding for ribosomal RNA are considered a reliable way to estimate the degree of relatedness among organisms. In 1977, Woese and Fox surprised biologists when they demonstrated profound differences in the sequence of ribosomal RNA that distinguished archaean species from Bacteria [1]. Much more shocking was their finding that the sequence of archaean ribosomal RNA was more closely related to eukaryotic cells than to other Bacterial cells...
