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Alexandra Worden and the eukaryote tree of life

AAAS member Alexandra Worden runs the microbial oceanography lab at the Monterey Bay Aquarium Research Institute. (Photo: Trudi Romeo)

There are trillions of tiny, single-celled organisms in the ocean that biologists know virtually nothing about. It drives AAAS member Alexandra Worden crazy.

The marine microbiologist is particularly intrigued by picoeukaryotessupersmall microbes she suspects play a much larger role in the climate change equation than they get credit for.

These "euks," as Worden calls them, are single-celled organisms that have a nucleus, are smaller than 2 microns and photosynthesize. They have been largely ignored by researchers because they are far less prevalent than cyanobacteria, which are the most abundant organisms on Earth.

"It was insane to me trying to describe the world based on just the easy stuff to measure and leave gapping holes," said Worden, who runs the microbial oceanography lab at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, California.

She has been working to fill that gap for much of her careeridentifying new species, studying their DNA and how they react to different environmental conditions. She received a $1 million "high-risk" microbiology research grant last year to help further this painstaking endeavor.

Her team is working to understand what limits euks' growth and hence how much carbon dioxide they convert into food, especially, as oceans warm and acidify. The more carbon consumed at the base of the marine food chain, the less enters the atmosphere as an Earth-warming gas.

Cyanobacteria have long been thought to lock away most of the carbon absorbed by the ocean. But while less abundant, euks are larger and grow faster so are taking up an equivalent amount of carbon, Worden said.  

"We have to look at these guys," she said.

Euks are gaining recognition, but still haven't been fully integrated into carbon cycle and climate prediction models. Those models "rely on the idea we know what's there and drives ecology," Worden said, but researchers are still discovering "deep branches in the eukaryote tree of life."

Worden's love of the sciences was cultivated early on by her mother. While her father, a lawyer, declared math an inappropriate dinner conversation, her mother had no problem discussing trigonometry at the table. She held a biochemistry Ph.D. from Harvard and partially home-schooled Worden and her three brothers in math and science.

"She had me putting electrons in orbitals in third grade," Worden said, who grew up in the Boston suburbs. "I was not up to task."

Worden attended Wellesley College, but took most of her science classes at Massachusetts Institute for Technology, where she identified with the other students. "I was a nerd, they were nerds," she said. At first she thought she wanted to pursue environmental engineering, but found there was too much still to learn about the natural world before trying to recreate it.

She majored in history because it allowed her to take a wider variety of science courses. She worried it would hinder her getting into graduate school, but the gamble paid off. She headed to the University of Georgia to earn a Ph.D. in ecology.

It was as a doctoral candidate studying picocyanobacteria that she became intrigued with picoeukyarotes.

"I was attracted to things that seem like a huge unknown," Worden said.

While clearly passionate about exploring and understanding the natural world, Worden was close to leaving science, turned off by the competitive culture. Nurturing mentors convinced her to stay, encouraging her to focus on what she loveddoing the science.

The 43-year-old is now facing the challenge of balancing work while raising two toddlers. She worries many women are pushed out of science because it doesn't accommodate family life well. "We lose a lot of diversity of thought, approach, and thinking because it's not really compatible," she said.

For Worden, the saving grace has been an understanding partner of 16 years. She met her husband while running experiments at MIT for her Ph.D. Their romance blossomed over late nights in the lab, the only time they could get access to equipment.

"Our tango friends couldn't understand why we were more excited about going to lab than to the next tango event," she said.

As a more established scientist, Worden relishes collaborating with others and helping students to think rationally and experience "light bulb moments" through hands-on discovery.

And while a million dollar grant might boost the ego of other researchers, Worden sees it only one way: as a means to answer ever more questions.