Survival is difficult anywhere, so why set up house in the Dead Sea, of all places? Although the chances of staying alive in the world's saltiest body of water are almost nil, this is precisely where bacteria called Haloarcula marismortui have elected to settle down. Stranger still, these creatures are themselves filled with liquid that is even saltier than the Dead Sea. What then is the secret of survival in salt?
The answer lies, at least in part, in the properties of the bacteria's proteins, which are different in structure from those of organisms living in conditions of "normal" salinity. One such important structural difference," uncovered by Dr. Felix Frolow, Dr. Michal Harel and Prof. Joel Sussman of the Weizmann Institute's Structural Biology Department, and their colleagues, was reported in the May issue of Nature Structural Biology.
The scientists grew crystals of one of the bacteria's most abundant proteins, ferredoxin, and determined their exact molecular structure using X-ray crystallography. They discovered that the ferredoxin of Haloarcula marismortui has an extra appendage compared with the ferredoxin of bacteria and plants that are not so "fond" of salt.
This appendage, as well as the rest of the protein's surface, has a relatively strong negative electric charge and therefore attracts water molecules and ions with a positive electric charge. These, in turn, create an unusually dense "envelope," which appears to shield the protein against the hostile environment.
Understanding such protective mechanisms sheds light on the limits to which living organisms may go in adapting to extremely high salinity, temperature or pressure -- conditions that may present themselves on earth or at future human outposts in outer space."
Prof. Sussman's team conducted its study in collaboration with Dr. Moshe Mevarech of Tel Aviv University and Dr. Menachem Shoham of the Case Western Reserve University School of Medicine, Cleveland, Ohio. Funding was provided by the U.S. Army Research Office.
The Weizmann Institute of Science is a major center of scientific research and graduate study located in Rehovot, Israel.