The research schooner Tara sailed the seven seas on a three-year inventory of plankton, the tiny microorganisms that float with the ocean currents.

It found adventure along the way — avoiding pirates in the Gulf of Aden and braving 100 mph winds — and gathered samples for the most complete inventory ever made of the tiny creatures that rival the world’s forests for ability to produce oxygen.

The Tara Oceans survey revealed a diversity of tiny marine life, most of which had never been genetically identified.

The sampling run was completed two years ago and results from it were published Thursday in five papers in a special edition of the journal Science.

UA microbiologist Matt Sullivan’s research team authored one of the papers and contributed to three others.

Sullivan’s team had a particular target — the viruses that infect the microbes that produce half the oxygen on Earth.

The results are the fruits of a longer undertaking for Sullivan and co-lead authors on the virus paper — Jennifer Brum, J. Cesar Ignacio-Espinoza and Simon Roux .

The team honed its filtering techniques in the artificial “ocean” at Biosphere 2 near Oracle, and developed new methods of genetic sampling before signing on for the task of analyzing 43 samples from Tara.

“We spent four years developing quantitative methods on the microscope and in the sequencing realm,” Sullivan said.

They made some surprising discoveries about the ocean viruses that affect production of half the Earth’s supply of oxygen.

Sullivan’s Tucson Marine Phage Lab catalogued more than 1.4 million genes and identified 5,476 species of viruses. The low number of species and genes was surprising, said Sullivan, who had earlier theorized that the oceans contained billions of genes related to viruses.

Microbial plants:
Small but mighty

Ocean viral research is a new field, said Brum, a post-doctoral researcher. Of the viruses characterized by Sullivan’s lab, only 39 were previously known to science, she said.

Finding them, and understanding how they work, is a critical step for knowledge of our planet and the changes taking place in it, she said.

“The small microbial plants in the ocean produce half the oxygen on the planet, roughly. They are the basis of the food web, what the smaller animals eat.”

The viruses infecting them are omnipresent, she said. “When you go swimming in the ocean, every mouthful has 200 million viruses in it. They are not infecting humans; they are infecting bacteria.

“They kill one third of the bacteria in the oceans every day. They transport genes between bacterial hosts and affect the evolution of microorganisms.”

Some contain genes needed for photosynthesis. “The virus is actually altering the amount of oxygen on the planet.”

“We need to understand who they are, where they are and what they’re doing, and eventually, ‘How do we put viruses into this big picture of how the world functions?’”

The models scientists use to predict the effects of climate change and ocean acidification lack information on the viruses, she said.

Sullivan said the research could one day lead to interventions in ocean ecology.

“The thing people don’t appreciate about viruses is that when they affect a cell, they metabolically reprogram it,” said Sullivan.

“Viruses directly have the genes to modify photosynthesis and nitrogen-cycling,” he said. “Viruses can be a tool for us to very positively change the abundance of microbes that we do or do not want.”

Some Researchers
are jumping ship

Sullivan leaves the UA this month for a new job and lab at Ohio State University.

“They have a really great microbiology department and I didn’t see a lot of opportunity for growing microbiological sciences at UA,” Sullivan said. “So I’m taking a leap.”

UA Dean of Science Joaquin Ruiz said Sullivan will be missed.

Sullivan’s lab, in the Department of Ecology and Evolutionary Biology, employs nine post-graduate and graduate researchers, five staff and some part-time undergraduates. Some of them, including Brum, will be leaving with him for Ohio State.

Ruiz said faculty loss this year is “more than I’ve seen in the past,” but he hasn’t fully analyzed why.

“It’s complicated. Some believe they have greater opportunities elsewhere. Others want to be closer to family or they don’t like the politics locally,” he said.

“We’ve been losing a lot of faculty lately,” he said. “I worry about it. If it continues, it’ll be a big problem.”

Contact Tom Beal at tbeal@tucson.com. On Twitter: @bealagram