How A Salt-Loving Fungus Survives In The Dead Sea
The Dead Sea ranks among the most unfriendly waters in the world due to its extreme saltiness. Sure it's a lot of fun for tourists floating on its waters, but you would never find a fish or any other marine creature swimming there. Algae, bacteria, and fungi, however, have been found in the landlocked lake, which is the lowest point on Earth.
Organisms that inhabit extreme environments like the Dead Sea survive by lying dormant for long periods of time or thriving in the salty conditions. The scientists studied the survival mechanisms of one of the organisms most commonly found in the Dead Sea: The filamentous fungus Eurotium rubrum (E. rubrum).
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"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 authors 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."
This research could prove to be a milestone for saline agriculture, as salt resistant genes can be incorporated to develop naturally salt-tolerant plant species.
The team first decoded the DNA of the fungus and sequenced, assembled, and annotated its 26.2 million bases. The team found that the genome contained just over 10,000 predicted genes. They also found that the E. rubrum proteins had higher aspartic and glutamic acid amino acid levels than expected. When the team compared that bacterium's gene families to those of two other halophilic species - Wallemia ichthyophaga and Hortaea werneckii - they found that high acidic residues were common in all three species, a general trait that all salt-tolerant microbes share.
Then, in order to understand its tolerance for salt, they grew samples of the fungus in liquid and solid media with levels of salinity ranging from zero to 90 percent of that in the Dead Sea. The researchers found that its spores were viable when grown in 70 percent diluted Dead Sea water. These results corresponded to the observation of algal blooms in the Dead Sea 20 years ago, when waters had been diluted due to rain.
Still trying digging deeper, they also looked at the bacterium's RNA, and found that the fungal cells need to keep cell membrane transport under tight control during conditions of high salinity. "This clearly indicates that the fungus tries to cope 'actively' with its extreme environment and does not simply fall into dormancy," the team noted, "as might be expected by the greatly reduced growth rates."
Along with contributing to saline agriculture, this work may also be useful for developing new strategies to improve biofuels production. For instance, the Department of Energy Joint Genome Institute and its partners are sourcing microbial and fungal enzymes for biomass pretreatment - a process that could lower the side effects of acids and high temperatures used in conventional methods. Environmentally benign organic salts could be a greener substitute to volatile organic solvents when converting biomass to biofuel.
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