Pandoraviruses. Credit: Chantal Abergel & Jean-Michel Claverie
Pandoraviruses. Credit: Chantal Abergel & Jean-Michel Claverie

Giant Viruses, Gut Microbes and Plastic Bacteria, Oh My

It’s been a good week for anyone who’s interested the smaller side of life. We’ve had giant viruses that are utterly unlike anything that we know of, bacteria that keep wasp species apart, microbes that thrive on plastic reefs, and more. I’ve written about these discoveries for Nature and The Scientist, so here are links to all of them. The giant viruses, in particular, blow my mind.

Giant viruses open Pandora’s box

The organism was initially called NLF, for “new life form”. Jean-Michel Claverie and Chantal Abergel, evolutionary biologists at Aix-Marseille University in France, found it in a water sample collected off the coast of Chile, where it seemed to be infecting and killing amoebae. Under a microscope, it appeared as a large, dark spot, about the size of a small bacterial cell.

Later, after the researchers discovered a similar organism in a pond in Australia, they realized that both are viruses — the largest yet found. Each is around 1 micrometre long and 0.5 micrometres across, and their respective genomes top out at 1.9 million and 2.5 million bases — making the viruses larger than many bacteria and even some eukaryotic cells.

But these viruses, described today in Science1, are more than mere record-breakers — they also hint at unknown parts of the tree of life. Just 7% of their genes match those in existing databases. “What the hell is going on with the other genes?” asks Claverie. “This opens a Pandora’s box. What kinds of discoveries are going to come from studying the contents?” The researchers call these giants Pandoraviruses. More

Gut microbes keep species apart

Mountain ranges and rivers can act as physical barriers that separate closely related species and keep them from cross-breeding. But the trillions of microbes in an animal’s guts could have the same role.

Robert Brucker and Seth Bordenstein, biologists at Vanderbilt University in Nashville, Tennessee, have found that the gut bacteria of two recently diverged wasp species act as a living barrier that stops their evolutionary paths from reuniting. The wasps have subtly different collections of gut microbes, and when they cross-breed, the hybrids develop a distorted microbiome that causes their untimely deaths.

“This is the most convincing evidence that the microbiome evolves with hosts over long time periods and might affect the speciation process,” says Bordenstein. More

Plastic fragments are changing the ecology of the oceans by providing havens for bugs and bacteria.

Many whales, albatrosses, and turtles have been found with plastic junk in their stomachs, while others have become entangled in packaging. These large animals have come to symbolize the growing problem of oceanic pollution. But a number of new studies suggest that floating plastics are also providing a new habitat—the “plastisphere”—for smaller marine residents, from insects to microbes.

Plastics have become the most common type of debris in the seas. Contrary to popular depictions of floating garbage islands, most of this junk consists of tiny fragments no bigger than a fingernail. Although they are small, these pieces can become trapped in large concentrations within circular ocean currents called gyres. Parts of the North Atlantic Gyre, for example, hold more than 50,000 plastic pieces per square kilometre.

The open ocean is low in nutrients and often likened to a desert. Now, we have these microbial reefs—pieces of confetti-like plastic that are their own ecosystem,” said Linda Amaral-Zettler from the Marine Biological Laboratory in Woods Hole. “We’re concerned about how these pieces are changing the nature of this large body of water.” More

Scientists are filling in the many uncharted branches of the tree of life.

The tree of life is dominated by microbes, but many large branches remain uncharted because scientists have been historically restricted to studying the small fraction of species that will grow in a lab. An international team of scientists has now begun to redress this bias, sequencing full genomes from single cells to bring the “uncultured majority” into view.

In total, the team identified more than 200 new microbial species belonging to 29 underrepresented or unknown lineages. And the results, published today (July 14) in Nature, were full of new metabolic abilities and genetic surprises.

“[There has been a] strong imperative to fill in the microbial tree of life,” said Philip Hugenholtz from the University of Queensland, one of the study’s leaders. “If you have an incomplete view of evolution—vastly incomplete in the case of microorganisms—you have a vastly incomplete understanding of biology.” More