Deep sea yields record-breaking bug
Sub-seafloor microbes perform ancient biochemical trick in scalding heat.
A heat-busting bug has been found that can create usable nitrogen at the extreme temperature of 92 °C breaking the old record by 28 °C.
The finding is more than a gee-whiz record breaker: it may also help to settle a long-running debate about how the ability to extract nitrogen from the air or seawater evolved, and perhaps help chemists to better mimic the process for industrial use.
Every living thing needs nitrogen, not least because it makes up part of DNA. But most nitrogen in the air is bound up in intractable twosomes, as N2. Only certain groups of microbes can wrestle nitrogen atoms free of this embrace so they can be used in cells a process called nitrogen fixation.
But when did this ability evolve? One theory is that the enzyme that makes nitrogen fixation possible (nitrogenase) evolved just once, a very, very long time ago. Another theory suggests that early bugs used the easier-to-obtain nitrogen from ammonia, which may have been around in relatively large quantities at the time. Under this theory, the ability to fix nitrogen evolved later, and was passed around laterally among species.
Vent of life
Mausmi Mehta and John Baross, both at the University of Washington in Seattle, went digging in an erupting hydrothermal vent on the floor of the Pacific Ocean to see whether they could find nitrogen fixers there. These mineral-rich hot spots are one of the top contenders for where life may have first evolved.
There is indeed a nitrogen fixer in this hot soup, they found. They think the bug's natural home is roughly 100 metres below the sea floor, in an oxygen-less world, clustered next to pockets of magma. The find supports the theory that the trick of nitrogen fixation evolved very early on.
Jonathan Zehr, who works on marine nitrogen-fixing at the University of California, Santa Cruz, says that the finding is important, but that he suspects the ultimate answer about the enzyme's evolution will be "somewhere in the middle". Perhaps the trick evolved once a long time ago, with species later losing the ability and regaining it through lateral transfer.
The find could also have commercial applications. Because nitrogen is so important to growing organisms, industry currently makes vast quantities of it, chemically, to use as fertilizer. If we could better understand how nitrogen fixation is performed by various bacteria, this might help to develop new ways to make it in the lab.
"Given the importance of nitrogen fixation in global agriculture and the creative exploitation of novel organisms by the biotechnology industry, a heat-stable nitrogenase is likely to find a useful industrial application," writes Douglas Capone of the Laboratory of Oceanography in Villefranche sur Mer, France, in an essay accompanying the new research.
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- Mehta M. and Baross J. Science, 314 . 1783 - 1786 (2006).
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