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September 25, 2004

Lightning, Bacteria, Life and Genetics

[Crossposted from GeneticFuture.org] - What do lightning and bacteria have to do with one another? Quite a bit, it turns out...

Global Gravy

To begin with, lightning and bacteria share the important job of providing the fundamental food for all of life on Earth: fixed nitrogen. Plants eat the nitrogen, animals eat the plants, and then the most barbarous of us animals eat one another. Pull nitrogen out of the pyramid, and the whole thing collapses.

nitrogen-cycle.gif

Our atmosphere stores a significant portion of our planet's reserve of pure nitrogen (N2). That said, most plants can't eat nitrogen until it gets fixed in some other compound, such as nitrate (NO3-), ammonia (NH3), or urea (NH2)2CO. As of today, we only know of two mechanisms in nature that facilitate the creation of these compounds:

  • Nitrifying Bacteria - which do the dirty work of turning plant and animal excretions and dead organisms into ammonia. Farther down the line, additional bacteria convert some of this ammonia into nitrites (NO2-) and nitrates (NO3-).
  • Lightning - which, as it blasts a path through the atmosphere, splits apart nitrogen molecules. The resulting promiscuous nitrogen atoms combine with oxygen to form nitrogen oxides (NO3-). Rain dissolves these into nitrates, which then wash to the surface of the Earth.

Lightning and bacteria -- strange bedfellows, don't you think? But wait, it gets weirder yet...

Genetic Partners-in-Slime

If the above recapitulation of the Nitrogen Cycle was yesterday's news for you, then you might find this factoid more interesting: Bolts of lightning appear to be responsible for facilitating gene transfer in soil bacteria. From New Scientist's website:

Scientists commonly use electricity to increase the permeability of bacterial cell membranes, making it easier to insert DNA. Now Sandrine Demanèche's team at the University of Lyon has provided the first evidence that nature may have been wise to this trick all along.

The researchers seeded soil samples with the E. coli bacterium, as well as fragments of DNA containing genes for antibiotic resistance. They zapped the soil with a simulated lightning strike, and found that many of the bacteria had acquired the resistance genes.

Bacteria are already known to take up and use foreign DNA released into the environment when other organisms die. Scientists knew this "horizontal gene transfer" occurs naturally in soil, but thought it was relatively rare. However, recent genomic research indicates that this gene take-up is widespread and has played a major role in the evolution of the bacterial genome.

"This result might help explain the discrepancy between the very low observed rates of gene transfer and the apparently wide distribution of DNA sequences among bacteria," says team member Timothy Vogel.

Yay lightning! Yay bacteria! And yow, what a kick in the pants when you appreciate how little we know about how genes go about spreading themselves. After all, if there is one thing genes "want", it's to get Somewhere Else. As such, the kinds of biological mechanisms genes code for will tend to express weirder and weirder means of gene transference as sex and pollination reach their natural limits...

Thanks to j.kimball's nitrogen cycle summary for the above diagram, and for refreshing my high-school biology understanding on this matter.
Posted by canton at 10:21 AM