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The researchers made an amazing discovery in the soil at the Harvard Forest in Petersham, Massachusetts. The team discovered giant viruses up to hundreds of times larger than other viruses.
Viruses are generally thought to be tiny infectious agents smaller than bacteria and human cells. But now researchers, including biologist Jeff Blanchard and Ph.D. student Lauren Alteio at University of Massachusetts at Amherst report the opposite.
"We were not looking for giant viruses," Blanchard said. "Our goal was to directly isolate bacteria from the environment to understand how microbial communities evolve in response to soil warming."
According to Blanchard, the work consisted of suspending the soil microbial cells in a mild detergent solution, adding a non-toxic DNA binding dye, and then using fluorescence activated cell sorting (FACS) to isolate the individual cells. He explained that this method captures giant viruses, whose genomes were extremely large, because of their similar size to that of bacteria.
Tanja Woyke is a senior scientist with the United States Department of Energy (DOE). Joint Institute of the Genome (JGI) who also collaborated on the study. Woyke suggested to the team to use mini-metagenomics, a new strategy that involves placing cells in small pools before sequencing the genome.
With this approach, researchers acquired DNA sequences from more than 2,000 individual cells and particles. They discovered 16 new giant viruses in the pools, which, according to Blanchard, was "a wonderful surprise and a very exciting new science".
Frederik Schulz, an expert in bioinformatics at JGI and co-lead author of the study, said, "The fact that we found all these giant virus genomes in the soil was particularly intriguing, as most giant viruses previously described in aquatic habitats. The metagenomic data generated here from a single sampling site contained many more new genomes of the giant virus than any other dataset I've seen so far. "
Schulz added: "In this study, we have collected 16 distinct giant virus genomes, but we are only scratching the surface. If we sample more on the same site, this number would double, triple or quadruple easily. "
The discovery of the giant virus is part of a series of ground-warming experiments conducted for many years in the research forest, located about 28 km northeast of the UMass Amherst campus.
"Not only did we discover many new giant viruses, but we did it with a considerable amount of soil," Blanchard said. "It would be nice to characterize these viruses one by one, it's a lot of talent and art. But it would be a project of several years. Finding 16 at once is quite overwhelming, and none of them is the same. If you think of all the soil of the world, if there are 10,000 species of bacteria in a gram of soil, about a teaspoon, imagine how many new giant viruses exist. "
The study is published in the journal Nature Communications.
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By Chrissy Sexton, Earth.com Editor
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