Viruses that eat bacteria outnumber every living thing on Earth combined
There may be more than ten million trillion trillion bacteriophages on the planet, more than all living organisms, bacteria included, put together. These viruses infect only bacteria, and up to 70 percent of marine bacteria may be carrying one. A century ago, doctors in the Soviet Union were already using them to treat infections.
A phage is a protein shell wrapped around a genome of DNA or RNA, which it injects into a bacterium to hijack the cell and make copies of itself. Some carry as few as four genes, others hundreds. They turn up wherever bacteria live; the French-Canadian microbiologist Félix d'Hérelle found them in sewers, polluted rivers and the stools of recovering patients. Bacterial viruses do not share a common ancestor, so they are scattered across many unrelated groups.
Hints came first from India. Ernest Hanbury Hankin noticed in 1896 that an unknown agent in the Ganges and Yamuna waters killed cholera bacteria and passed through the finest porcelain filters. In 1915 the British bacteriologist Frederick Twort found a tiny agent that destroyed bacteria, but war and lack of money halted his work. D'Hérelle, working independently at the Pasteur Institute, announced on 3 September 1917 an invisible microbe that attacked the dysentery bacillus, named it the bacterium-eater, and in 1919 carried out the first clinical use of a phage.
Phage therapy flourished in Soviet Georgia in the 1920s and 1930s, pioneered by Giorgi Eliava with d'Hérelle's help, and was used on Red Army soldiers. The West dropped it once antibiotics arrived, partly because they were easier to make and store, and partly because Soviet research was published in Russian or Georgian and viewed with suspicion during the red scare. With antibiotic resistance rising, interest has returned: in 2016 an American patient in a coma from a drug-resistant infection recovered after emergency treatment with phage cocktails.
Phages also transformed biology. The Hershey–Chase experiment of 1952, which used them, convinced scientists that DNA rather than protein carries genetic information, and a Nobel prize followed in 1969. Since 2006, US regulators have approved phage products that kill Listeria on cheese and meat.
Source: Bacteriophage
