A team of scientists from Israel, Germany and the US are studying Eurotium rubrum, a filamentous fungus found in the depths of the Dead Sea, to understand why it tolerates salt so well. Their findings may help agronomists develop hardier varieties of fruits and vegetables that can be grown in brackish water. This goal has become more important than ever, as fresh groundwater deteriorates and increases in salinity in parts of the world undergoing accelerated desertification, the scientists said.

The team is studying E. rubrum’s genome to find out what makes it survive and grow in high-saline environments. The group is led by Eviatar Nevo from the University of Haifa in Israel, Igor Grigoriev of the US Department of Energy Joint Genome Institute (DOE JGI), and Gerhard Rambold of the University of Bayreuth, Germany. The team’s findings are described in the May 9 issue of Nature Communications. 

The Dead Sea has 34.2 percent salinity, making it the fourth saltiest body of water on earth, 9.6 times as salty as the ocean. The high level of salt in the Dead Sea is a boon to tourism, enabling swimmers to float without trying. However, it is not very conducive to life, hence the sea’s name.

Over the years, scientists have discovered numerous life-forms, such as algae, bacteria and fungi, that are able to survive the harsh Dead Sea environment. But most of the life-forms in the Dead Sea area live on the beach and go dormant when inundated with salt. E. rubrum, among other bacteria and fungi, is different and does well in the water itself.

In tests, Tami Kis Papo, a student at the University of Haifa, recreated conditions that prevailed in an algae bloom in the Dead Sea 20 years ago, when the sea was 30% diluted. In the experiment, the fungus grew as it did two decades ago. Papo also checked the effects of higher and lower salinity on E. rubrum, in both cases noting that growth either slowed considerably or stopped.

At higher salinity levels, the fungus survived, although it stopped growing. Studying this phenomenon, Alfons R. Weig of the University of Bayreuth determined that, at higher levels, the fungal cells were very tightly controlled to prevent salt from “leaking” into them. The study, the team said, “indicates that the fungus tries to cope ‘actively’ with its extreme environment and does not simply fall into dormancy as might be expected by the greatly reduced growth rates.”

The team believes that the secret to E. rubrum’s salt tolerance is in its genetic tolerance to acids. E. rubrum proteins had higher aspartic and glutamic acid amino acid levels than expected, and, when compared to genes in two other halophilic (salt-loving) species, the team found that high acidic residues were common in all three species.

The ability to grow and survive in these increased salinity levels could hasten the development of crops that are more tolerant to brackish conditions, with hardier strains able to grow in the saltier water that has crept into formerly fresh water tables, the team believes.

“Understanding the long-term adaptation of cells and organisms to high salinity is of great importance in a world with increasing desertification and salinity,” the team wrote. “The observed functional and structural adaptations provide new insight into the mechanisms that help organisms to survive under such extreme environmental conditions, but also point to new targets like the biotechnological improvement of salt tolerance in crops. In principle this discovery could revolutionize saline agriculture worldwide by laying the groundwork of understanding necessary to appropriately using salt-resistant genes and gene networks in crops to enable them to grow in desert and saline environments,” they added.