Eureka!???

Eureka is perhaps the word most associated with a startling scientific discovery. It’s thought to be attributed to Archimedes, an ancient Greek mathematician, for a discovery he made about the displacement of water by stepping into his bathtub. Anyway, it’s a nice story or myth, but I’ve never actually heard it said by any scientist I know, well maybe once or twice in a bar.

I’ve been fortunate to make several fundamental discoveries during my career, but I’ve never had a Eureka moment. I do occasionally get to do what I call the Eureka dance, which is an awkward set of movements whereby I simultaneously try to pat myself on the back for being clever, and kick myself in the ass for being so dumb. That’s usually the way it is with discovery. After the long drawn out process of convincing yourself that what you’ve discovered is real, you wonder how you could not have seen it all along. It does engender a certain sense of humility, in part because with a little extrapolation you realize just how many things are going on in our natural world that are right under our noses, and will be amazing discoveries, but we just haven’t realized it yet.

For the past couple of weeks, I thought I might be approaching a Eureka moment. The bacteria I study use iron for food. They get their energy by converting ferrous iron to rust, some of them can literally ‘eat nails’, which is pretty wild when you think about it. When they eat iron, they respire using oxygen, just (well not exactly just, but pretty close) to the way we do. When oxygen’s not present, which is often the case in the microbial world, many bacteria can also use the chemical nitrate to respire in place of oxygen.

Based on its genes, this one iron-eating bacterium I have been studying seemed like it should be able to grow with iron using nitrate instead of oxygen. To test this I made a growth medium and replaced the air (containing oxygen) with only nitrogen gas and carbon dioxide, and added some iron and some nitrate, and voila the bacteria grew! Nice discovery. I then did a control where I used the same growth medium, but left out the nitrate and the oxygen, and voila, they grew.  Eureka! an even greater discovery.

For some complex chemical reasons, which I don’t fully understand myself, I’ve harbored a notion that maybe these bacteria could do something special with iron to produce their own oxygen. Not like plants that use light and photosynthesis to produce oxygen, but a little chemical trick using iron and water that might give them their own small source of oxygen. Such a process would be really unique in biology, and count as a big discovery.  Was this what I was seeing? Of course, I wanted to believe it.

It also happens that I recently acquired a really sensitive oxygen sensor. Before I announced my amazing new discovery to the world I wanted to confirm there was really no oxygen present in the bottles I was using to grow these bacteria. I had already ruled out that oxygen was not leaking in through the stoppers I used to seal the bottles.  But, low and behold, when I used my new oxygen sensor I found there was a tiny amount of oxygen still present, almost below the detection of sensors I had used previously to test this.

So foiled again, it wasn’t because these bacteria were magically producing oxygen, but because my technique for removing oxygen wasn’t as good as I had thought. However, I also noticed that the bacteria were growing differently with this really small amount of oxygen. These bacteria spin filaments of rust when they grow, and with really low oxygen, they made especially nice filaments, as shown in this picture taken with my microscope.

iron filaments

These rust filaments are very thin, which is also why they don’t appear red in the photomicrograph. A hundred of them bundled together into a single strand would be the width of a human hair. One reason we’re interested in these rusty filaments is because they could be used as a signature for detecting life on Mars. Mars is called the ‘red planet’ because it has lots of iron on it. I’ve seen fossilized filaments produced by these bacteria (or their relatives) that are a half a billion years, but look like they were made yesterday. So if someday we return a high powered image from Mars of some Martian soil and it’s full of these little filaments, that will be a Eureka!!! moment. These filaments of rust could also be used to catalyze some interesting chemical reactions, if we could figure out how to control their growth. Discovering how the concentration of oxygen effects their production is a step in this direction.

That’s how it is with discovery, eureka morphs from being wrong into a fascinating new research question.

Happy Holidays!

dis-1 red green

Here’s my bacteria holiday image in Christmas colors. The bacterial cells are green, the iron filaments are red. This is way smaller than the head of a pin.

David Emerson

About David Emerson

David Emerson is a professional scientist at the Bigelow Laboratory for Ocean Sciences who studies bacteria that live literally between a rock and a hard place. The views expressed here are his alone.