New Study Shows Huge Phages Are Everywhere

Huge phages—everywhere!
“An understudied component of the microbial ecosystem is the predator—which is the phage,” says Banfield. Scientists believe most phages are small, so they usually look for phages with experiments that exclude large particles. To learn more about the roles phages play in different ecosystems, Banfield’s group took a more open-ended approach known as metagenomics. Instead of leaving out larger particles, they sequenced all of the DNA in the samples. This allowed them to find phages of any size. They took samples from different environments, including human saliva, animal feces, freshwater lakes, oceans, hot springs, soil, and material hundreds of meters down in the earth’s crust.

The researchers reconstructed over 350 huge phage genomes, each with over 200,000 DNA base pairs. They put together a 735,000 base pair phage genome—the largest on record. This is more than ten times the reported average size of a phage genome.

The researchers found huge phages in all of the environments they sampled. They infect a variety of different one-cell host organisms. “Large phages have been found before, but they were spot findings,” says study co-first author Rohan Sachdeva. Sachdeva is a bioinformaticist in the Banfield lab. “What we found in this paper is they are essentially ubiquitous. We find them everywhere.” This suggests that huge phages are not an anomaly, but a fundamental part of earth’s many ecosystems.

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