Looking Out for Life

Although Curiosity has not found evidence of life on Mars, NASA announced yesterday that its suite of dirt analyzers works perfectly. Meanwhile new discoveries on Earth and the planet Mercury continue to imply the possibility of extraterrestrial life. On ERV, Abbie Smith marvels at the extremophile bacteria that have been locked under an Antarctic ice sheet for the last 2800 years, “happily (but slowly!) generating proteins in their hypersaline, super cold, no oxygen, ton of iron environment!” And though Smith would love to work in Antarctica, she says it “might be more fun to go to Europa with a shovel.” On Starts With a Bang, Ethan Siegel explains the counterintuitive presence of water ice on Mercury, writing “any rocky planet with no atmosphere and a sufficiently small axial tilt should have permanently shadowed craters at its poles, which will contain ices and other frozen materials common to that Solar System.” Which gives life on Mercury, approximately, a snowball’s chance in hell.

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20/20 Hindsight

Even the best and brightest can get things wrong, which is why science depends on corroboration to get things right. On Respectful Insolence, Orac investigates the conviction of six Italian seismologists for failing to warn people about an earthquake that killed 300. Orac writes “‘earthquake swarms’ are not uncommon in the L’Aquila region” and “a medium-sized shock in a swarm forecasts a major event within several days only 2% of the time.” But for accurately assessing the risk of a major event, the government employees have been sentenced to six years in prison for manslaughter. On Starts With a Bang, Ethan Siegel outlines the requirements for a truly scientific prediction, adding “some natural phenomena are simply presently beyond the reach of science.”  Meanwhile, on The Weizmann Wave, new research contradicts the hypothesis that certain lake bacteria can substitute arsenic for phosphate in their DNA. Rather than exploit the local abundance of arsenic, these bacteria “have actually evolved to reject it ever more efficiently.”

Cracking Microbial Code

On Tomorrow’s Table, Pamela Ronald shares a breakthrough in the study of bacterial communication. Although bacteria have been known to use a limited chemical vocabulary, for the first time they have been observed to use a protein as a signalling mechanism. Ronald writes, “Ax21 is a small protein. It is made inside the bacterial cell, processed to generate a shorter signal and then secreted outside the bacterium.” In the species studied, perception of Ax21 caused nearly 500 genes—ten percent of the bacterium’s genome—to change expression. Thus galvanized, individual bacteria assemble into “elaborate protective bunkers” called biofilms, producing “a virulent arsenal including ‘effectors’ that are shot directly into the host to disrupt host defenses.” As Ronald says, “this process transforms the bacteria from a benign organism to a fierce invader.” While the bacterium in question infects a rice plant, Ax21 and similar proteins may play the same role in other pathogens—including those that infect animals and humans. But we multicellular types are not defenseless: Ronald and her team have shown, for the first time, that a host’s immune receptors can overhear the microbial call-to-arms and prepare for war. 2011 Nobel Laureate Bruce Beutler also discusses Ronald’s work as it relates to his own, beginning at 40:45 in his Nobel Lecture of Dec. 7.