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“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.” – Neil Armstrong (1930-2012)

Fresh Reads from the Science 'o sphere!

Sunday, February 18, 2007

Repulsive Bugs

Every life science student knows the drill:

Eukaryotes = clever cells with membrane-bound organelles. Ah, such intricate elegance; did I mention the nucleus? The Golgi apparatus?

Prokaryotes = stupid bugs with no organelles. Their only job in the known universe is to make us sick and miserable.

Unfortunately Nature has a habit of not adhering to neat categories. Or more correctly, our neat categorizing.

In 1975, Richard Blakemore discovered a group of bacteria that respond to magnets. If you point the North pole of a magnet at them, they swim toward it.

No big deal, you say. Maybe the bacteria randomly swallowed up tiny pieces of iron and got attracted to the magnet.

Then, Prof. Blakemore turned the South pole of the magnet at the bacteria, and guess what?

They swam away.

Now that's odd. Ferrite particles should be attracted to either pole of a magnet. The bacteria didn't just contain ferrite, they contained magnetite.

In addition, even if they contained magnetite, the magnetic field should have flipped them around and attracted them anyway. So they didn't just react passively to a magnetic field - they were actively swimming away from the S-pole. This ability to move in response to a magnetic field is called magnetotaxis.

It gets even odder:

1. Magnetic bacteria don't simply eat random pieces of magnets floating around. They biosynthesize their own ferrite particles by absorbing Fe (III) ions from their environment, producing particles with very consistent size (50-100nm) and shape.

2. Somehow in the process of making these particles, they get magnetized.

3. They synthesize each magnetite particle inside one membrane-bound vesicle.

4. On top of that, the magnetosomes (vesicle + magnetite inside) are arranged in a neat chain. Chain formation is a highly organized and regulated process. In fact, the magnetosome chain is the most complex structure in a prokaryote cell.

So magnetotactic bacteria do have membrane-bound organelles. And because they are anaerobic, they die quickly in the presence of oxygen and don't cause much trouble for people.

Scientists hypothesize that these bacteria use their magnetosome chains to orientate them and allow them swim deeper into the soil, away from the dangerous oxygen-rich top layer.

These bizarre magnetic bacteria are not only a scientific curiosity, but because they can synthesize tiny, single-domain magnets of consistent size, they are also potentially useful industrial tools. Magnetosomes can be isolated by sonicating the bugs (breaking them open) and then centrifugated and purified.

This is what purified magnetosomes look like:

In addition, the magnetite particles are enclosed in a phospholipid membrane, which makes them biocompatible. Thus, they are suitable for a wide variety of biotech and medical applications.

During the 1970s and '80s, progress in this field was slow due to a number of technical reasons. Recently, the isolation of new strains and new techniques for handling these strains allowed significant progress to be made.

Prof. Dirk Schüler of the Magneto-Lab at the Max Planck Institute in Germany is a leading expert on one species of magnetotactic bacteria, the Magnetospirillum gryphiswaldense. He believes that current technology for magnetosome production has already reached industrial feasibility.

This means that we can expect to see some "attractive" applications for these bugs within the next few years!

Ha ha ha! That joke fell completely flat.

In fact it was rather repulsive.

Would you like to know more?

About magnetic bacteria
Magnetotactic Bacteria: you can download a Nature Reviews article on "Magnetosome Formation in Prokaryotes" here

About other bizarre organisms
Planarian worm