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BIOFUEL BARONS? The Indian Institute of Science's Ramachandra (left) and Balasubramanian are searching for a way to efficiently harvest oil from diatoms that could be used as biofuel.
© SCIENTIFIC AMERICAN/SASWATO DAS

BANGALORE, India—In the ongoing hunt for alternative fuel sources that are also cost-effective, researchers are looking into making biofuel from genetically engineered diatoms, a type of single-celled algae with shells made of glasslike silica.

These microscopic plants, commonly observed as a brown skin coating submerged stones in rivers and lakes and as phytoplankton in seas and oceans, typically contain oil droplets inside their cells. The oil is a food source for the plants in lean times. Scientific analysis of diatom oil has shown that it is very suitable for use as biofuel, says T. V. Ramachandra, a professor of ecological sciences at the Indian Institute of Science (IISc) here who is working on this project with IISc researchers Durga Mahapatra and Karthick Balasubramanian, along with Richard Gordon, a radiology professor at the University of Manitoba in Winnepeg.

Sitting in his book-lined office in a leafy corner of the IISc campus in Bangalore, Ramachandra proposes it might just be possible "to milk diatoms for oil just as we milk cows." He and his colleagues have been talking about a solar panel that could extract this oil instead of producing electricity.

The oil can be as much as a quarter of the total mass of a diatom cell, and if a way could be found to efficiently wrest it from diatoms, he adds, a hectare of "diatom cultivation could produce 10 to up to 200 times the oil that is produced by soybean cultivation," Ramachandra says. (This estimate has been borne out by other, independent research groups, as well.)

The researchers propose creating a biological solar panel, which will contain diatoms instead of photovoltaic cells. Diatoms would float about in a nutrient-rich water solution and produce oil when exposed to sunlight. Diatoms already secrete silica by exocytosis—a biological process by which cells direct secreted material outside the cell walls. If diatoms could be made to similarly secrete the oil they produce, then it could be easily harvested. (Because the oil is used as a reserve nutrient—like fat—diatoms have evolved no mechanism to secrete it.)

New diatom species
Diatoms may have other advantages when it comes to oil production. They multiply rapidly—some species double their biomass in as little as five hours. Diatoms are also quite numerous, with the estimated number of species exceeding one million. "There are 2,500 species of diatoms in India alone," says Balasubramanian, who is writing his doctoral thesis on these algae. He discovered three new species in India while hunting for those with the most oil content.

Ramachandra and his colleagues propose to genetically modify diatoms by manipulating the genes that produce oil so that they enhance its production. "It may be possible to genetically engineer diatoms so that they exocytose [release] their oil droplets," the researchers wrote in a paper outlining their thoughts, published in a recent issue of the American Chemical Society's journal Industrial & Engineering Chemistry Research: "This could lead to continuous harvesting with clean separation of the oil from the diatoms, provided by the diatoms themselves."