![Bacterial Endospores
• Certain genera of Gram-positive bacteria, such as
Bacillus, Clostridium, Sporohalobacter, Anaerobacter
and Heliobacterium, can form highly resistant, dormant
structures called endospores.
• In almost all cases, one endospore is formed and this is
not a reproductive process, although Anaerobacter can
make up to seven endospores in a single cell.[81]
Endospores have a central core of cytoplasm containing
DNA and ribosomes surrounded by a cortex layer and
protected by an impermeable and rigid coat.
• Endospores show no detectable metabolism and can
survive extreme physical and chemical stresses, such as
high levels of UV light, gamma radiation, detergents,
disinfectants, heat, pressure and desiccation.](https://image.slidesharecdn.com/bacteria-220518131924-bd5fef88/85/bacteria-ppt-19-320.jpg)
bacteria.ppt
- 1. Bacteria Antonie van Leeuwenhoek, the first microbiologist and the first person to observe bacteria using a microscope. Source : the free encyclopedia
- 2. Bacteria • Bacteria were first observed by Antonie van Leeuwenhoek in 1676, using a single-lens microscope of his own design. • The name bacterium was introduced much later, by Christian Gottfried Ehrenberg in 1838. • Louis Pasteur demonstrated in 1859 that the fermentation process is caused by the growth of microorganisms, and that this growth is not due to spontaneous generation. (Yeasts and molds, commonly associated with fermentation, are not bacteria, but rather fungi.) Along with his contemporary, Robert Koch, • Pasteur was an early advocate of the germ theory of disease. • Robert Koch was a pioneer in medical microbiology and worked on cholera, anthrax and tuberculosis. In his research into tuberculosis, Koch finally proved the germ theory, for which he was awarded a Nobel Prize in 1905 • In Koch's postulates, he set out criteria to test if an organism is the cause of a disease; these postulates are still used today.
- 3. Bacteria • Though it was known in the nineteenth century that bacteria are the cause of many diseases, no effective antibacterial treatments were available. • In 1910, Paul Ehrlich developed the first antibiotic, by changing dyes that selectively stained Treponema pallidum—the spirochaete that causes syphilis—into compounds that selectively killed the pathogen. • Ehrlich had been awarded a 1908 Nobel Prize for his work on immunology, and pioneered the use of stains to detect and identify bacteria, with his work being the basis of the Gram stain and the Ziehl-Neelsen stain.
- 4. Bacteria • A major step forward in the study of bacteria was the recognition in 1977 by Carl Woese that archaea have a separate line of evolutionary descent from bacteria. • This new phylogenetic taxonomy was based on the sequencing of 16S ribosomal RNA, and divided prokaryotes into two evolutionary domains, as part of the three- domain system.
- 6. Bacteria Morphology A small number of species even have tetrahedral or cuboidal shapes. More recently, bacteria were discovered deep under the Earth's crust that grow as long rods with a star-shaped cross-section. The large surface area to volume ratio of this morphology may give these bacteria an advantage in nutrient-poor environments. This wide variety of shapes is determined by the bacterial cell wall and cytoskeleton, and is important because it can influence the ability of bacteria to acquire nutrients, attach to surfaces, swim through liquids and escape predators.
- 7. Bacteria Morphology • Most bacterial species are either spherical, called cocci (sing. coccus, from Greek kókkos, grain, seed) • or rod-shaped, called bacilli (sing. bacillus, from Latin baculus, stick). Elongation is associated with swimming. • Some rod-shaped bacteria, called vibrio, are slightly curved or comma-shaped; others, • It can be spiral-shaped, called spirilla, or tightly coiled, called spirochaetes.
- 8. Bacteria Morphology • Many bacterial species exist simply as single cells, others associate in characteristic patterns: Neisseria form diploids (pairs), • Streptococcus form chains, and • Staphylococcus group together in "bunch of grapes" clusters. • Bacteria can also be elongated to form filaments, for example the Actinobacteria. • Filamentous bacteria are often surrounded by a sheath that contains many individual cells. Certain types, such as species of the genus Nocardia, even form complex, branched filaments, similar in appearance to fungal mycelia.
- 10. Bacterial cell structure Intracellular structures • The bacterial cell is surrounded by a lipid membrane, or cell membrane, which encloses the contents of the cell and acts as a barrier to hold nutrients, proteins and other essential components of the cytoplasm within the cell. • As they are prokaryotes, bacteria do not tend to have membrane- bound organelles in their cytoplasm and thus contain few large intracellular structures. • They consequently lack a nucleus, mitochondria, chloroplasts and the other organelles present in eukaryotic cells, such as the Golgi apparatus and endoplasmic reticulum. • Bacteria were once seen as simple bags of cytoplasm, but elements such as prokaryotic cytoskeleton, and the localization of proteins to specific locations within the cytoplasm have been found to show levels of complexity. These subcellular compartments have been called "bacterial hyperstructures". Intracellular structures
- 11. Bacterial cell structure Intracellular structures Many important biochemical reactions, such as energy generation, occur by concentration gradients across membranes, a potential difference also found in a battery. The general lack of internal membranes in bacteria means reactions such as electron transport occur across the cell membrane between the cytoplasm and the periplasmic space. However, in many photosynthetic bacteria the plasma membrane is highly folded and fills most of the cell with layers of light-gathering membrane. These light-gathering complexs may even form lipid-enclosed structures called chlorosomes in green sulfur bacteria. Other proteins import nutrients across the cell membrane, or to expel undesired molecules from the cytoplasm. Intracellular structures
- 12. Bacterial cell structure Extracellular structures • Around the outside of the cell membrane is the bacterial cell wall. Bacterial cell walls are made of peptidoglycan (called murein in older sources), which is made from polysaccharide chains cross-linked by unusual peptides containing D-amino acids. • Bacterial cell walls are different from the cell walls of plants and fungi, which are made of cellulose and chitin, respectively. • The cell wall of bacteria is also distinct from that of Archaea, which do not contain peptidoglycan. The cell wall is essential to the survival of many bacteria, and the antibiotic penicillin is able to kill bacteria by inhibiting a step in the synthesis of peptidoglycan.
- 14. Bacterial Biofilm • Bacteria often attach to surfaces and form dense aggregations called biofilms or bacterial mats. • These films can range from a few micrometers in thickness to up to half a meter in depth, and may contain multiple species of bacteria, protists and archaea. • Bacteria living in biofilms display a complex arrangement of cells and extracellular components, forming secondary structures such as microcolonies, through which there are networks of channels to enable better diffusion of nutrients.
- 15. Bacterial Biofilm • In natural environments, such as soil or the surfaces of plants, the majority of bacteria are bound to surfaces in biofilms. • Biofilms are also important in medicine, as these structures are often present during chronic bacterial infections or in infections of implanted medical devices, and bacteria protected within biofilms are much harder to kill than individual isolated bacteria.
- 16. Bacterial Biofilm • A biofilm is an aggregate of microorganisms in which cells adhere to each other and/or to a surface. • These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS). • Biofilm EPS, which is also referred to as slime, is a polymeric conglomeration generally composed of extracellular DNA, proteins, and polysaccharides in various configurations. • Biofilms may form on living or non-living surfaces, and represent a prevalent mode of microbial life in natural, industrial and hospital settings.
- 17. Bacterial Biofilm • The microbial cells growing in a biofilm are physiologically distinct from planktonic cells of the same organism, which, by contrast, are single-cells that may float or swim in a liquid medium. • Microbes form a biofilm in response to many factors, which may include cellular recognition of specific or non- specific attachment sites on a surface, nutritional cues, or in some cases, by exposure of planktonic cells to sub- inhibitory concentrations of antibiotics. • When a cell switches to the biofilm mode of growth, it undergoes a phenotypic shift in behavior in which large suites of genes are differentially regulated.
- 18. Bacterial Endospores Variations in endospore morphology: (1, 4) central endospore; (2, 3, 5) terminal endospore; (6) lateral endospore
- 19. Bacterial Endospores • Certain genera of Gram-positive bacteria, such as Bacillus, Clostridium, Sporohalobacter, Anaerobacter and Heliobacterium, can form highly resistant, dormant structures called endospores. • In almost all cases, one endospore is formed and this is not a reproductive process, although Anaerobacter can make up to seven endospores in a single cell.[81] Endospores have a central core of cytoplasm containing DNA and ribosomes surrounded by a cortex layer and protected by an impermeable and rigid coat. • Endospores show no detectable metabolism and can survive extreme physical and chemical stresses, such as high levels of UV light, gamma radiation, detergents, disinfectants, heat, pressure and desiccation.
- 20. Bacterial Endospores • In this dormant state, these organisms may remain viable for millions of years, and endospores even allow bacteria to survive exposure to the vacuum and radiation in space. • Endospore-forming bacteria can also cause disease: for example, anthrax can be contracted by the inhalation of Bacillus anthracis endospores, and contamination of deep puncture wounds with Clostridium tetani endospores causes tetanus.