Wednesday, March 23, 2011

Oozing along with Beggiatoa (part I)

This beauty is from some mud I looked at in the recently-finished microbial diversity lab.

It's Beggiatoa (Bedgy-a-toe-uh, “Bedgy” to its friends), a pretty common resident of the top layer of muddy sediments; it likes a little oxygen, but not very much. Bedgy oozes up and down in the sediments, between oxygen-rich water and anoxic mud to get oxygen levels juuuuuust right.

Bedgy is easy to find, as common as mud, and absolutely hypnotic. Here’s another specimen under higher magnification, looking like a jeweled necklace. I sat and watched this string of cells oozing by for a few minutes minutes, and I never saw the beginning or end of it. You MUST watch it full-screen.

Your high-school biology textbook probably had a general equation for photosynthesis that went like so:

H2O + CO2 --> C6H12O6 + O2

The atoms in water and carbon dioxide are rearranged to produce glucose and oxygen. This takes a lot of energy, and the energy comes from light.

Bedgy is an important bacterium in the history of science. It was the first organism that was observed to perform “chemosynthesis,” rather than photosynthesis. If you look at the periodic table, you’ll see that Sulfur is in the same column as Oxygen, and that Sulfur behaves chemically in some of the same ways as Oxygen. What’s kind of neat is that Bedgy does this:

H2S + CO2 --> C6H12O6 + S (and some SO4)

A difference between Oxygen and Sulfur is that Oxygen is soluble—it dissolves in water, and floats away in our atmosphere when it’s made by photosynthesis. However, the sulfur that Bedgy produces isn’t soluble—so it forms little semi-solid pellets, and that’s what those little yellow dots are. And unlike photosynthesis, the energy for what Bedgy is doing comes from respiration, not light—so, “chemosynthesis,” not photosynthesis. That same high-school biology textbook with the equation about photosynthesis also says that all life ultimately depends upon energy from the sun; Bedgy is there, oozing along and proving them wrong.

When one of my students looked through the 'scope and saw this, the reaction was "WOW!" followed immediately by "Wait--how does it do that?"

Stay tuned.

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