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At this point they initiate the reproductive cycle, resulting in lysis of the host cell. As the lysogenic cycle allows the host cell to continue to survive and reproduce, the virus is replicated in all offspring of the cell. An example of a bacteriophage known to follow the lysogenic cycle and the lytic cycle is the phage lambda of E. coli. [54]
In their experiments, Hershey and Chase showed that when bacteriophages, which are composed of DNA and protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not. Hershey and Chase and subsequent discoveries all served to prove that DNA is the hereditary material.
The experiment involved radioactively labeling either protein or nucleic acid of the bacteriophage T2 (a virus that infects bacteria) and seeing which component entered Escherichia coli upon infection. They found that nucleic acids but not protein were transferred, helping resolve controversy over the composition of hereditary information.
In 1952, Alfred Hershey and Martha Chase confirmed that the genetic material of the bacteriophage, the virus which infects bacteria, is made up of DNA [4] (see Hershey–Chase experiment). In 1953, James Watson and Francis Crick discovered the double helical structure of the DNA molecule based on the discoveries made by Rosalind Franklin. [5]
What he discovered was that when, after UV irradiation, two or more "dead" phage entered the same bacterial cell, they often became alive again and produced normal live progeny. [9] This was the first example of reactivation of cells or organisms that had been damaged by radiation.
Following prolonged incubation in media that they previously failed to ferment, several species acquired fermentation powers which originally they did not enjoy. We now know that these mutant individuals able to ferment novel sugars arose in culture , and came to dominate the population .
d'Hérelle was a self-taught microbiologist. In 1917 he discovered that "an invisible antagonist", when added to bacteria on agar, would produce areas of dead bacteria. The antagonist, now known to be a bacteriophage, could pass through a Chamberland filter. He accurately diluted a suspension of these viruses and discovered that the highest ...
In 1922, John Kunkel Small (1869–1938) discovered that insects could act as vectors and transmit virus to plants. In the following decade many diseases of plants were shown to be caused by viruses that were carried by insects and in 1939, Francis Holmes, a pioneer in plant virology, [37] described 129 viruses that caused disease of plants. [38]