Breaking down barriers

The institute's scientists have developed a preliminary treatment that allows the lignin in the plant to be removed without damaging the sugars

The biomass of plants can be converted into clean and environmentally friendly fuel, but this conversion is not yet carried out on a large scale, partly because of its high cost. However, a visual representation of the process at an atomic level may optimize biomass conversion - according to a study carried out by scientists from the Weizmann Institute of Science and the National Renewable Energy Laboratory in the US.

The study, which was published in the scientific journal Science, confirmed the theory that one of the biggest obstacles in converting biomass is lignin, the hard polymer that strengthens plants. The conversion usually begins with pre-treatment, where the lignin is crushed mechanically, or destroyed using chemicals. In the new study, the scientists developed an innovative method, which made it possible for the first time to observe the destruction of lignin at the resolution of individual molecules and atoms, using an advanced laser microscope. The pictures showed that the lignin does interfere with the enzymes to break down complex sugar molecules in the plant cell walls. These sugar molecules can later be turned into ethanol, a type of biofuel. Thanks to this discovery, the scientists characterized the ideal pretreatment: the lignin must be removed without causing damage to the sugars.

The scientists compared two methods for breaking down sugars. One method relied on single enzymes extracted from fungi. In the other method, the decomposition is done by the cellulosome - a natural molecular aggregate consisting of several enzymes, through which bacteria, fungi and other microorganisms break down the cellulose in plants. The scientists discovered that the individual enzymes penetrated deeper into the plant cells, while the cellulose acted mainly on their surface. Understanding the mechanisms involved in breaking down cellulosic biomass may help design enzyme systems that will more efficiently break down plant cell walls.

The cellulosome was discovered about three decades ago by Prof. Ed Bayer from the Department of Biological Chemistry at the Weizmann Institute and Prof. Raphael Lemmed from Tel Aviv University. In the current study, Prof. Bayer collaborated with scientists from the National Renewable Energy Laboratory in the US, including Dr. Shi-Yu Ding, who conducted post-doctoral research in Bayer's laboratory in the late 90s. Dr. Ding and Dr. Yu-San Lee developed the methods for visualizing the effects of different chemicals on the plant cell wall, in different resolution ranges, the largest of which is a million times larger than the smallest: from a millimeter to a nanometer (millionth of a millimeter). The other team members in the USA were Dr. Michael Himmel, Dr. Yuning Zeng and Dr. John Baker.

The research findings may help researchers develop an optimal pre-treatment for biomass, and improve the activity of the enzymes that break it down. These improvements will increase the yield of ethanol, and reduce the cost of biofuel production.

Historical note: The cellulosome in this study was produced from a bacterium called Clostridium thermocellum, which belongs to the type of bacteria historically associated with the Weizmann Institute and the State of Israel. Dr. Chaim Weizmann used another bacterium of the same type, Clostridium acetobutylicum - known today as the "Weizmann bacterium" - to produce acetone during the First World War. Recently, Weizmann Institute scientists discovered another link between past and present: genetic studies showed that the "Weizmann bacterium" produces its own cellulose.