To survive in cold, salty environments, it helps to be a little less negative and a little more flexible, at least if you're a protein.
In an article published March 13 in PLOS One, scientists describe subtle changes in the proteins of a salt-loving Antarctic microbe. These differences could explain how some microbes survive in extreme environments. Similar changes could allow microbes to survive even on Mars, said Shil DasSarma, a biochemist at the University of Maryland School of Medicine who led the study.
Only a few studies have looked at the biochemical mechanisms that allow proteins to work in low-temperature, high-salt conditions, DasSarma said. He added that this is the first comparative genomics study of species from the same phylogenetic group.
"To me that is the one most interesting scientific aspect of the study. With comparative genomics, we consider both phylogeny and physiology," he said. "Here the phylogeny is conserved, so we can glean something about the physiology."
The amino acid substitutions, which the team investigated further in a second study (2), change the arrangement of the atoms within the internal regions of the proteins. These changes may make a protein more flexible, allowing it to work even in the cold, salty waters of Deep Lake, DasSarma said.
The cold-adapted microbes also have fewer negative charges on the surface of their proteins compared to Haloarchaea from more mild climates. Microbes living in warm, high-salt conditions use negative charges to keep a hydration shell around their proteins so they don't dry out. However, at freezing temperatures changes in the molecular organization of the water molecules in the hydration shell could impair protein function.
In the cold-adapted proteins, however, fewer negative charges at their surfaces could reduce their interactions with water, reducing the effect of freezing on protein activity. "This is probably a trick the microbe came up with to allow the proteins to be more flexible and keep working even in cold, salty conditions," DasSarma said.
To test the idea, he and his team plan to insert the cold-adapted proteins into the temperate-climate Haleoarchaea and observe whether they can survive harsh, Antarctic-like conditions. Those studies, DasSarma said, might lead to better man-made materials and give scientists a few more hints about how life might be possible elsewhere in the universe.
“The results certainly broaden the concept of where microorganisms are possible and shows how they can survive in a salty, cold environment,” said Michael Meyer, lead scientist for NASA's Mars Exploration Program, who was not involved in the study.
1. DasSarma S, Capes MD, Karan R, and DasSarma, P. (2013). “Amino Acid Substitutions in Cold-Adapted Proteins from Halorubrum lacusprofundi, an Extremely Halophilic Microbe from Antarctica.” PLoS ONE 8(3): e58587.
2. Karan et al. (2013). “Cloning, overexpression, purification, and characterization of a polyextremophilic β-galactosidase from the Antarctic haloarchaeon Halorubrum lacusprofundi. BMC Biotechnology, 13:3.