Subterranean microbes in the sea perform an age-old biochemical trick in boiling heat
A heat-resistant bacterium was discovered, which is able to produce unstable nitrogen at an extreme temperature of 92 degrees Celsius, thus breaking the previous record of 28 degrees Celsius!
The finding is much more than a surprising record breaking. It may also help resolve an ongoing scientific debate over how the ability to utilize nitrogen from the air or seawater evolved, and may help chemists better mimic this process for industrial purposes.
Every living thing needs nitrogen, not only because nitrogen atoms are part of the DNA molecule. However, most of the nitrogen in the air is tightly bound in pairs of atoms as N2. Only certain groups of microbes are able to free nitrogen atoms from the strong bond of N2, and use them in the cell. This process is called nitrogen fixation.
When did this unique ability develop? One theory holds that the enzyme that enables nitrogen fixation, nitrogenase, evolved only once, a very long time ago. All bacteria capable of fixing nitrogen have split off evolutionarily from the same ancestral bacterium in which the enzyme nitrogenase developed. Another theory holds that ancient bacteria used easier-to-obtain nitrogen, nitrogen from ammonia, which was probably abundant at the time. The ability to fix nitrogen was not essential then and developed later and passed laterally between different species.
Mosami Mehta and John Bruce, both of the University of Washington in Seattle, excavated a hydrothermal vent on the floor of the Pacific Ocean and looked for nitrogen fixers there. These mineral-rich hotspots are one of the most prominent contenders for places where life first began.
Indeed, in the hydrothermal vent that was tested, inside the "rich and hot soup" is a nitrogen fixer. This is probably an organism whose natural environment is 100 meters below the seabed, in an oxygen-free world, near magma pockets. The finding supports the theory that the nitrogen fixation trick developed very early in evolution.
Jonathan Zahar, who works on marine nitrogen fixation at the University of California, Santa Cruz, says the finding is important, but he thinks the ultimate answer to enzyme evolution lies "somewhere in the middle." The ability to fix nitrogen may have evolved once a very long time ago with species that subsequently lost this ability and reacquired it later through lateral (horizontal) transfer from species to species.
The finding could also have commercial implications. Since nitrogen is so important to growing organisms, large amounts of it are now produced in industry chemically, to be used as a fertilizer. If we can better understand how biological nitrogen fixation is carried out by different bacteria, we may be able to develop in the future new ways, biotechnologies, to produce nitrogen in the laboratory or in industry.
"When you take into account the importance of nitrogen fixation in global agriculture and the creative use of new organisms by the biotechnological industry, heat-resistant nitrogenase is a discovery that is likely to have many beneficial industrial uses," writes Douglas Capone in an accompanying article to the publication of the research findings.
