With concerns about global warming and rising oil prices, there is renewed impetus behind efforts to harness microorganisms as a way of reducing worldwide reliance on fossil fuels.  Some companies are keen on exploiting photosynthetic microbes, whereas others are counting on other ways to marshal microbial metabolic prowess. Here are highlights describing several recent developments in which microbial activity is at the heart of the technology. However, critics continue to question whether these or other microbial- based technologies can meet critical "sniff tests," such as scale-up and efficiency, to make them competitive with fossil fuels.

"Helioculture" depends on genetically engineered photosynthetic microorganisms to convert "widely available"-but undisclosed-chemical nutrients along with brackish or seawater into fuels and "solar chemicals," according to Joule Biotechnologies of Cambridge, Mass. The raw material is not biomass, according to Joule's CEO Bill Sims. "To a certain extent, you can consider our feedstock to be carbon dioxide," he says. Solar energy is captured in a special "solar converter, [which] is a flat panel device and inside is a solution of nonfresh water, the nutrients, and highly engineered photosynthetic microorganisms." Fermentation products include ethanol and hydrocarbons, some of which could be used for making plastics.

The Joule research team now plans to scale up its experiments for evaluation outdoors "somewhere in the Southwest," according to Sims. One nearterm goal is to determine whether its helioculture approach can yield 20,000 gallons of ethanol per acre per year. If all goes well, plans call for locating a pilot plant in the same region because sunlight is abundant but the land is not well suited for agriculture.

Meanwhile, PetroAlgae in Melbourne, Fla., also is depending on sunlight to generate fuels via microorganisms such as algae, diatoms, and cyanobacteria that will be grown in "large, open-pond bioreactors," says company representative Andrew Beck. "Our technology precisely manages exposure to light to dramatically increase the growth and productivity of indigenous microorganisms," or "micro-crops." They yield diesel fuel and also a high-protein liquid and a mash, rich in carbohydrates and lipids, that could be used as animal feed.

Last April, PetroAlgae signed a commercial licensing deal with GTB Power, a consortium in mainland China and Taiwan, while others are being negotiated elsewhere in Asia as well as in Europe, the Middle East, Africa, and South and North America, according to Beck. The April agreement calls for building ten 5,000-hectare, commercial units in China starting late this year.

Sunlight does not appear to be part of the recent $10-million agreement between oil giant British Petroleum (BP) and Martek Biosciences of Columbia, Md. The latter company is focused on microorganisms that can convert sugars into lipids through a heterotrophic process that requires neither direct sunlight nor carbon dioxide. The sugars come from many sources, including feedstocks that BP is already using or investigating such as sugar cane, woodchips, or grasses. One promising feature of the partnership is that, for more than two decades, Martek has used its fermentation technology on an industrial scale to produce lipids for infant formula and food supplements, according to company spokeswoman Cassie France-Kelly. "The BP/Martek approach is reliant on technologies proven at scale, rather than technologies being explored by other companies in the lab stage of development," she says.

However, some experts are skeptical about relying on microbially fermented sugars as a means for solving current dependence on fossil fuels to meet global energy needs. "The largescale production of transportation fuels will not be economical or sustainable using sugar produced by photosynthesis as feedstock for microbial conversion to biodiesel," says chemist Gerard C. Dismukes at Princeton University in Princeton, N. J., who also says that turning microalgal lipids into biofuels is not practical. "A direct process must be found."

"Making a smooth transition to a world supported by sustainable resources is the defining challenge of our time, with transportation among the most important pieces of this challenge," says Lee Lynd, an environmental engineer at Dartmouth College in Hanover, N.H. "In looking for technologies that can achieve meaningful petroleum displacement, we need to apply critical sniff tests to make sure that there is real potential to achieve this aim."

Barry E. DiGregorio

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