Caption: Bacteriophages (viruses) escaping from a dying bacterial cell (Streptococcus sp.). This bacteriophage was discovered in freshwater near a sewage outlet. A bacteriophage, also known as a phage, is a virus (virion) that infects a bacterium (bacterial cell). It consists of a head (capsid), containing the genetic material (either ssRNA, dsRNA, ssDNA, or dsDNA) and usually a tail and tail fibers (not seen), which the phage uses to attach to a specific receptor sites (including lipopolysaccharides, teichoic acids, proteins and flagella) on the bacterium. This specific binding means that a bacteriophage can only infect certain bacteria bearing receptors that they can bind to. Once attached to the cell surface genetic material is injected into the bacterium, taking over the bacterium's own cellular machinery and forcing it to produce more copies of the bacteriophage. When sufficient numbers have been produced the phages escape from the bacterium by cellular lysis, killing the bacterium in the process. The whole process takes about 15-20 minutes. Phages are estimated to be the most widely distributed and diverse entities in the biosphere. Phages were discovered to be anti-bacterial agents and were put to use with varying degrees of success. Due to antibiotic resistance in certain bacteria strains phage therapy is being widely investigated. Phages are also found to be more abundant in freshwater and marine habitats and can cause significant mortality of bacterioplankton.
Magnification*: x21,335
Type: SEM
Copyright 2012 Dennis Kunkel Microscopy, Inc.
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