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Chaim Weizmann would surely be amazed to learn that the bacterium linked to his struggle for the creation of the State of Israel now promises to perform a new international feat.
It was while working as a research chemist in Manchester shortly before World War I that Weizmann found a bacterium that produced acetone and butyl alcohol. Though a senior university professor advised him “to pour the stuff down the sink,” Weizmann continued to study the bacterium. History would prove him right. When the war broke out, acetone – needed for producing gunpowder and usually made by distilling wood – was in short supply, and the British government asked Weizmann to develop large-scale production of acetone from maize with the help of his bacterium. He managed to set up the manufacture of considerable quantities of the vital chemical, an achievement that greatly raised his prestige and helped him fight for the proclamation of the historic 1917 Balfour Declaration, which promised the Jewish people a “national home” in Palestine.
Current Weizmann Institute research might allow Dr. Weizmann’s bacterium, called Clostridium acetobutylicum, to reveal its prowess in a new field: It may be employed to decrease pollution while producing useful chemicals. In this guise, the bacterium may be harnessed for breaking down cellulose, the main component of plant cell walls and the most abundant type of biomass on Earth.
Cellulose is a stable chain of linked sugar molecules that gives wood its remarkable strength and serves as the basic building block for many textiles and paper. To get an idea of its sturdiness, consider the following: A chain of more than seven sugar units is insoluble, and cellulose can contain up to 10,000! In nature, cellulose fibers from trees and plants are degraded by microorganisms in soil and water that possess a molecular machine called a cellulosome – a large protein complex consisting of several enzymes. The cellulosome splinters the tough, insoluble cellulose into soluble sugars, which can then re-enter the plant growth cycle. However, natural cellulosomes are not good at breaking down cellulose in such man-made products as paper. As a result, billions of tons of discarded paper fail to decay in landfills across the planet, creating an environmental problem of enormous proportions.
Prof. Edward Bayer of the Weizmann Institute’s Biological Chemistry Department and Prof. Raphael Lamed of Tel Aviv University discovered the cellulosome in 1983 and in subsequent years elucidated its architecture. Now they are building “designer” cellulosomes that, among numerous other applications, would be able to degrade paper waste effectively – either on their own or inside a microorganism. Using genetic engineering and combining different structural elements in a Lego-like design, Bayer and Lamed seek to optimize cellulosome performance.
After trying out hundreds of different artificial cellulosomes, the collaborative team selected one consisting of three cellulose-degrading enzymes. The enzymes of this artificial cellulosome have two complementary modes of action: one chops up cellulose by catching it in a cleft, Pacman-style; the other continuously clips the cellulose chain while passing it through a tunnel-like opening. The synthetic cellusome is still far from being ready for use in waste management, but in a laboratory dish it takes only about a day to churn up finely chopped paper into a syrup of two-unit soluble sugars. “Nature can’t deal with paper,” says Bayer, “but we may be able to coax the cellulosome into handling tasks that were not foreseen by evolution.”
While Bayer makes use of purified designer cellulosomes, it may also be possible to employ his findings to improve the function of cellulosomes inside whole micro-organisms, and that’s precisely the goal of several research teams around the world. This latter option brings us back to Dr. Weizmann’s bacterium: Its recently deciphered genome was found to contain the genes for a cellulosome. However, like a long-forgotten piece of machinery discovered in the basement during a spring cleaning, this cellulosome is defective and it’s currently not being used by the bacterium. Relying on Bayer’s research, his colleagues in Toulouse and Marseille have recently given this cellulosome a genetic overhaul, trying to convince the historic bug to generate acetone and butyl alcohol from paper waste rather than from maize, as in Dr. Weizmann’s work. Thus the bacterium that once helped create the State of Israel might one day make an industrial comeback thanks to Israeli research.
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