The bacterium Clostridium thermocellum
and a handful of close relatives are the only organisms known to break down one of the hardest materials in nature – the cellulose found in trees and tough, woody plants. This unique ability could be quite valuable: Scientists are working to adapt it to recycling cellulose-based waste and producing biofuel. Now, some 50 years after it was identified and 30 years after the discovery of the cellular organelle that enables it to digest cellulose, the genome of a particularly efficient strain of this bacterium has been sequenced, along with that of a mutant strain used in research. The genome was announced
in the Journal of Bacteriology
Profs. Ed Bayer
of the Weizmann Institute’s Biological Chemistry Department and Raphael Lamed of Tel Aviv University were the first to discover the cellulose-digesting mechanism in Clostridium thermocellum
. This mechanism, an organelle they named the cellulosome, breaks the long, sturdy chains of sugars in cellulose molecules into shorter, soluble sugars. Their finding was based on a mutant strain they created in the lab that enabled them to isolate the structures. In the 30 years since that discovery, Bayer and Lamed have made steady progress elucidating exactly how the cellulosome works, as well as creating new versions that are more efficient and function in different conditions. “At this point,” says Bayer, “we can take the cellulosome apart and put it back together again like Lego. But until a year or two ago, the idea of getting a complete sequence of the strain we have been working with, known as YS, was just a dream.”
Bayer and Lamed worked with Drs. Steven Brown and Martin Keller and their team at the Bioenergy Science Center in Oak Ridge, Tennessee, as well as Bayer and Lamed’s students Ely Mora and Ilya Borovok of Tel Aviv University and Yuval Shoham of the Technion-Israel Institute of Technology, Haifa, to sequence the two strains.
Several relatives of the Clostridium thermocellum
strains have already had their genomes sequenced. In fact, a somewhat distant relative, Clostridium acetobutylicum
– which goes back to Weizmann Institute founder Dr. Chaim Weizmann, who used it to ferment acetone from maize in WWI – was sequenced not long
ago in Bayer’s lab. To the surprise of the researchers, this genome was found to have a defunct version of the cellulosome gene cluster.
Now, Bayer and his colleagues plan to compare the various genomes to look for clues to cellulosome efficiency, the ways the production of these organelles is regulated in nature and, hopefully, pointers for furthering the design of artificial cellulosomes for producing biofuel.
Prof. Ed Bayer’s research is supported by the Brazilian Friends of the Weizmann Institute of Science. Prof. Bayer is the incumbent of the Maynard I. and Elaine Wishner Professorial Chair of Bio-Organic Chemistry.