Bacteriophages
A bacteriophage is a virus. A virus is any pathogen that can only replicate in the living cells of other organisms. They are not considered "alive" by most scientists because of their relatively simple structure compared to even the simplest life forms. In fact, some viruses have as few as 1300 nucleotides -- whereas humans have 3 billion. They say that all the DNA in one human cell, when stretched out, would be roughly 6 feet long. For many viruses, that length could be measured in micrometers.
Viruses only do one thing: make more of themselves. Many viruses, such as bacteriophages, do this by consuming their host. The word "bacteriophage" is derived from "bacteria" and "phagein," which is Greek for "devour." The below image shows the anatomy of a bacteriophage.
In order for a bacteriophage to reproduce, it must first find a cell. It has no way of propelling itself so it must float around until it comes in contact with a receptor on the surface of the cell. Its tail fibers attach around the receptor and flex to bring its base plate closer to the surface until it is bound there. It is able to do this because of ATP in each tail. Then, the bacteriophage's genetic material in its head is pumped into the cell. Once this occurs, the bacteriophage is, for all intents and purposes, "dead."
But that's not the end of it -- the cell's ribosomes start translating the viral mRNA instead of cell mRNA. As a result, instead of doing normal cell things such as synthesizing proteins, the cell starts making copies of the bacteriophage using the mRNA as a blueprint. The cell ceases all normal function and only makes these copies until its membrane collapses and many new bacteriophages are released.
Here's a video of the process.
In 1896, Ernest Hankin collected a sample of water from the Ganges River that cholera bacteria. He noticed that something was killing the cholerae but could not figure out what. It remained a mystery until 1915, when Twort discovered the extremely tiny little entities responsible, bacteriophages. His findings were later confirmed by a scientist known as Félix d'Hérelle who took part in this discovery.
D'Hérelle conceptualized a practical application for bacteriophages, a process called phage therapy. Phage therapy is the use of bacteriophages (and/or other bacteria-killing viruses) to fight bacterial infection. Phage therapy gained support from medical professionals in the US and Soviet Georgia, but in the US its practice was short-lived as antibiotics, considered a better method than phage therapy, was discovered only several years after. However, phage therapy is currently being revisited in research as a counter to anthrax and botulism. Here is a culture of bacillus anthracis (anthrax) awhile after bacteriophages were added.
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