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Bacteria and Viruses by Britannica Educational Publishing

By Britannica Educational Publishing

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Consequently, endospores do not possess metabolic activity until nutrients become available, at which time they are able to differentiate from spores into vegetative cells. Only one spore is formed inside each bacterial cell during sporulation. The formation of a spore begins with invagination of the cytoplasmic membrane around a copy of the bacterial chromosome, thus separating the contents of the smaller cell from the mother cell. The membrane of the mother cell engulfs the smaller cell within its cytoplasm, effectively providing two concentric unit membranes to protect the developing spore.

Mutant strains of S. pneumoniae that have lost the ability to form a capsule are readily taken up by white blood cells and do not cause disease. The association of virulence and capsule formation is also found in many other species of bacteria. A capsular layer of extracellular polysaccharide material can enclose many bacteria into a biofilm and serves many functions. Streptococcus mutans, which causes dental caries, splits the sucrose in food and uses one of the sugars to build its capsule, which sticks tightly to the tooth.

The flagellum is attached at its base to a basal body in the cell membrane. The protomotive force generated at the membrane is used to turn the flagellar filament, in the manner of a turbine driven by the flow of hydrogen ions through the basal body into the cell. When the flagella are rotating in a counterclockwise direction, the bacterial cell swims in a 19 7 Bacteria and Viruses 7 straight line; clockwise rotation results in swimming in the opposite direction or, if there is more than one flagellum per cell, in random tumbling.

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