by Danielle Venton

It is the stuff of science fiction: A robotic alien landing pod descends upon a living host. Flexing its landing gear, the invader lowers its nether bits near the surface of the organism and injects instructions for the replication of more robot pod invaders. The organism becomes packed with ever more invaders until it explodes and dies.

This, essentially, is the nightmare bacteria live with as the prey of bacteriophages (“phages” to their friends). These bacteria-infecting viruses are the most abundant form of life on the planet. Surveys in seawater turn up around 10 phages for every bacterial cell. Whether phages can be considered to be truly alive, however, is debatable. Like other viruses, they cannot replicate on their own. To make more like themselves, they integrate into the host’s genes and hijack the machinery of the cell. They run the show from the inside.

In pictures captured with scanning electron microscopes, most phages resemble a cross between a spider and pin-headed robot. The head, holding the DNA payload—their injectable control system—sits atop a long column, supported by spindly leg-like tail fibers. Since they are structurally quite simple, phages are easy to control and tinker with experimentally. We can, in other words, take over the phages that take over bacteria. Human-controlled phages have helped researchers uncover many fundamental principles of biology, including what a gene is and how genetic information is read.

Phages may also be evolutionary heroes as key drivers of genetic exchange among single-celled organisms such as bacteria. They are able to swap genes from one organism or environment to another, as they incorporate into a host genome. Phages are found nearly everywhere bacteria are be found, amid the E. coli in our gut, for example, on the lips of the person sitting next to you or floating free in the ocean. Despite their ubiquity, however, phages likely have a biogeography all their own. Recent studies show some phages are everywhere on Earth (or nearly so), while others may be endemic (uniquely found in) to certain areas — like the single-celled organisms on which they feed on.

The extent of phage diversity is still a grand mystery. About 95 percent of bacteria can’t be grown in a lab—we, in essence, don’t know what they eat—and so the phages that infect those bacteria can’t be grown either. One way researchers are trying to circumvent this problem is through “viral metagenomics” — collecting and sequencing all the viruses, of which phages are a special variety—in an environment. This method can spotlight particular phages or phage genes that, if they are superabundant or found in certain niches, might be ecologically important. It is a fancy, genetic form of fishing.

Phages were first discovered in the early 20th Century in association with disease causing bacteria. In the time before antibiotics, they were immediately seized upon to help treat infections. Our enemy’s enemy is our friend. After the discovery of penicillin and other chemical antibiotics in the 1940s, interest in therapeutic phages declined in the West, but continued in Russia and other areas of the former Soviet Union. And it’s possible a medicinal dose of fighting “spider-bots” may be in your future. Concerned about the rise of multiple-antibiotic resistant bacterial strains, some Western microbiologists are returning to therapeutic phages. It may be time to welcome our viral robot overlords—or maybe “inner lords” is the better phrase–once again.


1. Martha Clokie, Andrew Millard, Andrey Letarov, Shaun Heaphy, Phages in Nature, Bacteriophage, January 2011, 10.4161/bact.1.1.14942.

2. Forest Rohwer, Global Phage Diversity, Cell, 18 April 2003, 10.1016/S0092-8674(03)00276-9.

3. Roger W. Hendrix, Jeffrey G. Lawrence, Graham F. Hatfull, Sherwood Casjens, The origins and ongoing evolution of viruses, Trends in Microbiology, November 2000, doi: 10.1016/S0966-842X(00)01863-1.

About the Author

Danielle Venton is a science writer and radio producer living in Northern California. She enjoys backpacking, competitive rowing, live music and fosters a special love for all under-appreciated life forms. Follow her on Twitter @DanielleVenton.