Unit 3: The Cell

What is a cell Capsule?

Many bacterial cells secrete some extracellular material in the form of a capsule or a slime layer. A slime layer is loosely associated with the bacterium and can be easily washed off, whereas a capsule is attached tightly to the bacterium and has definite boundaries. Capsules can be seen under a light microscope by placing the cells in a suspension of . The capsules exclude the ink and appear as clear halos surrounding the bacterial cells. Capsules are usually polymers of simple sugars (polysaccharides), although the capsule of is made of polyglutamic acid. Most capsules are hydrophilic (“water-loving”) and may help the bacterium avoid desiccation (dehydration) by preventing loss. Capsules can protect a bacterial cell from ingestion and destruction by. While the exact mechanism for escaping phagocytosis is unclear, it may occur because capsules make bacterial surface components more slippery, helping the bacterium to escape engulfment by phagocytic cells. The presence of a capsule in is the most important factor in its ability to cause pneumonia. Mutant strains of S. pneumoniae that have lost the ability to form a capsule are readily taken up by white cells and do not cause . The association of virulence and capsule formation is also found in many other species of bacteria.

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microbiology: Bacteria (eubacteria and archaea)

Microbiology came into being largely through studies of bacteria. The experiments of Louis Pasteur in France, Robert Koch in Germany, and others in the late 1800s established the importance of microbes to humans. As stated in the Historical background section, the research of these scientists provided proof for the germ theory of disease and the germ theory of fermentation. It was in their...

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A capsular layer of extracellular polysaccharide material can enclose many bacteria into a biofilm and serves many functions., which causes , splits the sucrose in food and uses one of the sugars to build its capsule, which sticks tightly to the . The bacteria that are trapped in the capsule use the other sugar to fuel their and produce a strong acid that attacks the tooth enamel. When Pseudomonas aeruginosa colonizes the lungs of persons with , it produces a thick capsular polymer of alginic acid that contributes to the difficulty of eradicating the bacterium. Bacteria of the Zoogloea secrete fibres of that enmesh the bacteria into a floc that floats on the surface of liquid and keeps the bacteria exposed to air, a requirement for the metabolism of this genus. A few rod-shaped bacteria, such as Sphaerotilus, secrete long chemically complex tubular sheaths that enclose substantial numbers of the bacteria. The sheaths of these and many other environmental bacteria can become encrusted with iron or manganese oxides.

Source: www.britannica.com
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