Huge bacteria-killing viruses blur the boundaries defining life

Hundreds of unusually large, bacteria-killing viruses with capabilities normally associated with living organisms, have been identified by a team involving UCL, blurring the line between viruses and living microbes. These phages - short for bacteriophage, so-called because they "eat" bacteria - are of a size and complexity considered typical of life, carry numerous genes normally found in bacteria, and use these genes against their bacterial hosts and other viruses, as reported in Nature . "In the DNA of these phages, we found parts of the system that bacteria use to fight viruses. It appears that some of these phages are using this system to target other viruses," said co-author Professor Joanne Santini (UCL Structural & Molecular Biology). "There are likely phage wars - viruses targeting other viruses - going on inside the gut microbiome of humans." The researchers, led by University of California, Berkeley, found these huge phages by scouring a large database of DNA that they generated from nearly 30 different Earth environments, ranging from the guts of premature infants and pregnant women to a Tibetan hot spring, a South African bioreactor, hospital rooms, oceans, lakes and deep underground. Professor Santini of UCL led analysis of phages from people in Bangladesh who had been drinking arsenic-tainted water, and phages from an arsenic-contaminated mine in northern Canada. Altogether the researchers identified 351 different huge phages, all with genomes four or more times larger than the average genome of viruses that prey on bacteria.