"Contrary to long-held assumptions, Earth's interior is not barren. In fact, a majority of the planet's microbes, perhaps more than 90 percent, may live deep underground. These intraterrestrial microbes tend to be quite different from their counterparts on the surface. They are ancient and slow, reproducing infrequently and possibly living for millions of years. [...] Subsurface microbes carve vast caverns, concentrate minerals and precious metals and regulate the global cycling of carbon and nutrients. Microbes may even have helped construct the continents, literally laying the groundwork for all other terrestrial life." The Mysterious, Deep-Dwelling Microbes That Sculpt Our Planet, an excerpt from Becoming Earth, by Ferris Jabr.
Enlarge/ This is an intact phage. A tailocin looks like one of these with its head cut off. (credit: iLexx)
Long before humans became interested in killing bacteria, viruses were on the job. Viruses that attack bacteria, termed "phages" (short for bacteriophage), were first identified by their ability to create bare patches on the surface of culture plates that were otherwise covered by a lawn of bacteria. After playing critical roles in the early development of molecular biology, a number of phages have been developed as potential therapies to be used when antibiotic resistance limits the effectiveness of traditional medicines.
But we're relative latecomers in terms of turning phages into tools. Researchers have described a number of cases where bacteria have maintained pieces of disabled viruses in their genomes and converted them into weapons that can be used to kill other bacteria that might otherwise compete for resources. I only just became aware of that weaponization, thanks to a new study showing that this process has helped maintain diverse bacterial populations for centuries.
Evolving a killer
The new work started when researchers were studying the population of bacteria associated with a plant growing wild in Germany. The population included diverse members of the genus Pseudomonas, which can include plant pathogens. Normally, when bacteria infect a new victim, a single strain expands dramatically as it successfully exploits its host. In this case, though, the Pseudomonas population contained a variety of different strains that appeared to maintain a stable competition.
The exact number of chickens, cows and pigs being transported on trucks, ships, planes and trains within the United States is difficult to pinpoint because there is no national system for tracking the movement of livestock.
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