Pond Scum Prized Again
as Potential Biofuel

Few people outside of the alternative-energy world knew about algae’s renaissance until last July. Exxon announced that it was plowing $600 million into algae research. The oil giant entered into a partnership with Synthetic Genomics, headed by Craig Venter, who pioneered sequencing the human genome in the 1990s. Over the past few years, Venter and his colleagues have been inserting genes into cyanobacteria to increase their production of lipids. Exxon expects to have small-scale plants in operation in five to 10 years.

The Wall Street Journal reacted to the news by declaring that the world had entered “the summer of algae.” Other companies were getting into the algae game as well. Solazyme, a corporation based in San Francisco, announced in June that its funding had reached $76 million. In September it announced that the Department of Defense had picked Solazyme to supply 20,000 gallons of fuel for Navy jets. Another company, Sapphire Energy, has $100 million in funding and promises that by 2011 it will be producing 1 million gallons of diesel and jet fuel from algae.

Yet these promises do not, in themselves, guarantee that algae fuel will actu-ally make financial sense. According to one estimate, it’s still 20 times more expensive to make than crude oil. And some skeptics don’t believe that the recent flurry of investment reflects any profound advances in dealing with the great problems associated with fuel derived from algae.

The best way to get a lot of lipids out of algae, for example, is to put them under stress. If Scenedesmus dimorphus is fertilized with a lot of nitrogen, for example, its cells will end up 20 percent lipids. On a low-nitrogen diet, that figure rises to 35 percent. Algae probably evolved this strategy as a way to survive temporary famines. In other words, it’s not something they can do indefinitely. If you stress algae for too long, says Peccia, “they’ll just give out.”

In 2008, Peccia, Zimmerman and Anastas decided to get into the algae fuel game. While corporations were just tweaking the algae and observing how many lipids they could get out, the Yale researchers chose a different strategy. “It’s a different way of going about things,” says Anastas, Teresa and H. John Heinz III Professor in the Practice of Chemistry for the Environment.

Peccia has been leading the team’s effort to get to know algae in their most intimate details. “We just want to understand how they operate, really in the most fundamental way,” says Peccia. For all the research that has gone into algae, for example, scientists still know nearly nothing about the genes they use to make lipids. No one has even sequenced the genomes of any of the lipid-rich microalgae. “We don’t really know how it all works,” says Peccia.

Because the genomes of microalgae are so big, Peccia and his colleagues have decided not to sequence all of their DNA. Instead, they’re just searching for the genes they use to make extra lipids. To find them, the scientists raise algae in different conditions. For instance, they rear some of their algae with a lot of nitrogen and some of them with barely any. The algae respond to these different conditions by switching on different genes. Peccia and his colleagues then rip open the algae. They fish out copies of the active genes, called messenger RNAs. From those molecules, the scientists can determine the sequence of the genes and start to gather clues about their function.

Peccia and his colleagues are now mapping out the gene networks that algae use to ramp up their lipid production. They hope that this knowledge will allow them to precisely manipulate algae into making more lipids with few side effects. It will then be possible to abandon the current brute-force methods of starvation.

Even if Peccia and his colleagues can manipulate algae to become champion lipid makers, however, they will still face some serious challenges in getting the organisms to thrive outside of a laboratory flask. The Earth’s waters are loaded with algae, and their diversity is so vast that scientists are only just starting to catalog it. Some of those species will inevitably slip into the tanks where engineers rear their designer algae. “They’re going to have to learn how to compete with these constant insults of micro-algae coming in,” says Peccia. If they don’t, they’ll get outcompeted and the tank will become overwhelmed by the wrong kinds of algae.

Peccia has been probing the biology of algae to look for ways that he can help them win in the real world. He and his colleagues have found that Scenedesmus dimorphus grows nicely when levels of carbon dioxide are high. In fact, they keep growing when other species of algae die from carbon dioxide poisoning. By pumping extra carbon dioxide into algae tanks, engineers may be able to keep the right species thriving. “If we don’t bubble high CO2 in, the natural algae outcompete it,” says Peccia.

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Top of Page | Fall 2009 | environment:YALE