Going for Green

 

What are the best crops to grow for biofuels? Corn and sugarcane, presently converted to ethanol in Brazil and the USA, consume large amounts of petrochemicals and arable land in cultivation, and using them for fuel is already beginning to drive up the price of food. The contribution of soybean- and canola-based biodiesel in Europe to overall fuel consumption is small and cannot be extended. A better alternative, according to a number of scientists, may be lying under the nearest rock or floating on a stagnant pond: algae.

 

Algae have a number of advantages over other sources of biofuel. For one, they can be grown on marginal soil or in salt water, without draining water resources. For another, they grow rapidly and could be harvested regularly throughout the year. And there is no waste – no seeds, stems or roots to discard. Algae plantations placed near power plants would capture much of the emitted carbon dioxide to use as building blocks for biofuel, thus creating “green energy.”

Finally, some kinds of algae produce oil – up to 50% of their mass. This oil, says Prof. Avihai Danon of the Institute’s Plant Science Department, can be easily xtracted and converted to bio-diesel, which could be used in today’s diesel engines without significant investment. Algae could yield an estimated 30 times the oil output of the best crop plants, and could satisfy the fuel needs of the USA and other heavily industrialized countries around the world.

 

Danon and Prof. Uri Pick of the Biological Chemistry Department have begun a new project that aims to create strains of algae that will excel at generating oil for biofuel. Their first step is to understand how and when the algae produce the oil. Like green plants, algae get their energy from the sun and store it as sugars or oils. But there is a limit to how much energy one alga – a single-celled organism – can utilize. In fact, too much sunlight can overload the alga’s system, stimulating the production of free radicals that can harm or even kill the cell. This limit creates a trade-off between oil production and growth, and the cell must decide in which to invest its energy. The scientists suspect that it is in times of stress that the algae build up their stores of oil.

 

The researchers are working on several different strains of algae that grow in different conditions and have different traits. They are developing the tools to identify and compare the genes that regulate the algal metabolism, making decisions whether to stockpile oil or spread out, whether to take in additional sunlight or put up protective sunscreens. “Once we’ve identified the genes, we should be able to develop the means to control these processes in the algae ourselves,” says Danon, “and hopefully create algae that can be an excellent, environmentally friendly source of fuel.”    

 

 

While the debate rages over the ecological and economic value of using food crops to produce fuel, Weizmann Institute scientists are taking a different approach that could potentially solve two environmental problems with one stone – or at least one bacterial enzyme complex.

 

One of the obstacles to creating biofuels from organic substances such as agricultural waste is that they contain large amounts of tough materials – mainly cellulose – that do not break down easily. (Corn and sugarcane, on the other hand, are rich in starch and sugar that can easily be turned into ethanol.) Prof. Ed Bayer of the Biological Chemistry Department has been researching bacteria that chew up cellulose, converting it to sugar that they then feed on. In the 1980s Bayer, together with Prof. Raphael Lamed of Tel Aviv University, discovered how the bacteria’s cellulose-degrading machinery works. The cellulosome, as they dubbed this molecular machine, is a group of enzymes that work as a team to chop up the long chains of repeating sugar units in cellulose molecules into short sugars that can be dissolved in water.

 

About 50 percent of landfill material is cellulose, mostly in the form of paper, and it continues to pile up year after year.

 

Breakdown is slow, partly due to landfill conditions and partly because the cellulose in such man-made products as paper turns out to be particularly hard for the bacterial cellulosome to digest. Bayer began tinkering with cellulosomes, adapting the bacterial machinery for turning plant cellulose into sugar into an effective tool for recycling paper. He and Lamed used genetic engineering techniques to create hundreds of different versions of the cellulosome, mixing and matching parts in their search for those that excelled at their new task. Prof. Gideon Schreiber, an expert in designing and altering protein-protein interactions, and Prof. Dan Tawfik, an expert in enzyme evolution, have joined the team to help design artificial cellulosomes with improved activity. The most recent version of the artificial cellulosome can potentially turn a lab dish full of finely shredded paper into simple sugar syrup in about a day.

 

Recently, this research has taken on new urgency. The simple sugars churned out in the process are ideal for conversion to ethanol, and the artificial cellulosome might be adapted to other cellulose-rich energy resources such as agricultural waste. Much research remains to be done before the process can be recreated efficiently on the industrial scale, Bayer cautions. Nonetheless, one day our cars may run on ethanol brewed from recycled trash.

If algae and bacteria can be engineered to produce such bio-fuels as biodiesel and ethanol, might they also generate such futuristic energy resources as hydrogen? Hydrogen could be the cleanest fuel of all, as its combustion leaves behind only water. But most present-day methods of producing hydrogen still involve processing fossil fuels.

 

In an ambitious project, a consortium of scientists from France, Spain, Sweden, the UK, Portugal and Israel, including Prof. Dan Tawfik of the Biological Chemistry Department, are investigating the possibility of creating a bacterium that will produce hydrogen cleanly and economically. The researchers have started with a strain of cyanobacteria (often called blue-green algae, though they are not true algae). These photosynthetic, single-celled organisms have a long history of producing materials we need: They’re credited with releasing oxygen into the early atmosphere (paving the way for the evolution of oxygen-breathing animals), and with fixing nitrogen in soils so that plants such as rice can absorb it.

 

The researchers plan to use a cutting-edge approach to developing the new bacteria. Rather than adapting one or two existing genes, they aim to equip the cyanobacteria with a whole new set of biological components engineered for specific functions. The multidisciplinary team will use a slew of techniques to accomplish this, including one developed by Tawfik – directing the evolution of enzymes in cell culture to produce cellular components that are highly efficient at carrying out desirable tasks.