The Laboratory in the News

Possible Bacterial Path of Antarctic Mercury

Livermore scientists Michael Thelen and Adam Zemla performed protein sequence analysis and structural modeling to predict key proteins involved in mercury methylation as part of research with the U.S. Geological Survey and the University of Melbourne to determine how highly toxic methyl mercury­—the product of methylation­—enters the Antarctic Ocean and accumulates in the marine food web there. The team’s findings were published in the August 1, 2016, online edition of Nature Microbiology and highlighted in the journal’s October 1, 2016, “News and Views” section.

Mercury from volcanoes and human activity such as burning fossil fuels circulates in the atmosphere, then deposits onto sea ice. Scientists are concerned that the fatty tissues of nearby fish could accumulate enough methyl mercury to pose a public health concern.

Thelen explains, “We examined the sequence data from DNA samples collected in sea ice and other Southern Ocean environments. A candidate sequence for a mercury methylation enzyme was found in a bacterial strain of the genus Nitrospina. Adam then used computational tools developed at the Laboratory to predict the structure and show how the active site of the enzyme would react with mercury.” The researchers’ analysis of samples collected in the second Sea Ice Physics and Ecosystem Experiment also found seawater under seasonal ice to contain significantly higher mercury concentrations than open-ocean water. Thelen adds, “Further research could physically confirm the proteins responsible for mercury methylation in Nitrospina and perhaps could help us find a way to inhibit or to reverse the reaction to reduce methyl mercury poisoning.”
Contact: Michael Thelen (925) 422-6547 (thelen1 [at] llnl.gov (thelen1[at]llnl[dot]gov)).

Game-Changing Forensics Technique Uses Hair Proteins

In an important breakthrough for forensic science, researchers have developed the first-ever biological identification method that unlocks the genetic information encoded in proteins of human hair. The groundbreaking technique could provide a second science-based, statistically validated way, in addition to DNA profiling, to identify people and link individuals to forensic evidence. The work by Lawrence Livermore, seven universities, and a Utah-based startup was announced in a paper published September 7, 2016, in the online journal PLOS ONE.

“We are in a very similar place with protein-based identification to where DNA profiling was during the early days of its development,” says chemist Brad Hart, director of Livermore’s Forensic Science Center and co-author of the paper. Proteins are chemically far more robust than nuclear DNA, which degrades quickly—a significant weakness in DNA-based forensics. In contrast, the team identified viable protein markers in human hair from skeletal remains in London cemeteries dating back 150 to 250 years. Hair samples from these and other subjects revealed each person to have unique protein markers that provide a forensically useful “fingerprint.” Proteins, including those in hair, are coded by the DNA that is unique to each person. The markers used by the scientists are protein variants resulting from DNA mutations known as single amino acid polymorphisms. The concept of basing identification on this facet of proteins was discovered by then Utah Valley University biochemist Glendon Parker, who later came to Lawrence Livermore, in 2013. The researchers are seeking to establish a set of 90 to 100 protein markers that would be sufficient to distinguish an individual among the world’s population using a single hair. Hart states, “This method will be a game-changer for forensics.”
Contact: Brad Hart (925) 423-7374 (hart14 [at] llnl.gov (hart14[at]llnl[dot]gov)).

Explanation for Iron Springing Back to Shape

A team of Lawrence Livermore physicists has performed a series of calculations shedding light on an unexpected way that iron transforms under dynamic compression. The team describes its first-principle calculations in a paper published in the August 19, 2016, issue of Physical Review Letters.

More than a decade ago, pioneering shock experiments revealed that single-crystal iron transforms under compression but then largely springs back to its original, intact lattice—a startling behavior that had defied understanding. “This reversible transformation is reminiscent of what happens in a shape-memory alloy,” explains Livermore materials scientist Michael Surh, lead author of the paper. Calculations by Surh and his colleagues used a carefully parameterized model of iron magnetic fluctuations that included the effect of the iron nuclei being moved as the material is squeezed. Previous work had neglected the role of magnetism.

In addition, a separate Livermore team’s shock-compression experiments showed that this transformation can take much longer than previously predicted. Surh explains, “It turns out that the different behavior—fast versus slow, reversible versus irreversible—seen in iron depends on its changing magnetism.” The researchers describe the role played by “magnetic frustration”—the competition between the tendencies of electron spins to be either aligned or misaligned with those of their neighbors. The team states that future simulations must also include magnetic effects to arrive at a fundamental understanding of the intriguing phenomenon.
Contact: Michael Surh (925) 422-2087 (surh1 [at] llnl.gov (surh1[at]llnl[dot]gov)).