Life without Oxygen

No, that’s not a reference to a Jordin Sparks/Chris Brown song, its the theme for the paper of the month.

This month, in expression of my gratitude to the kind folks at Open Access publisher BioMedCentral for sending me a “clone” of their very adorable mascot Gulliver (picture left), I have decided to do a post spotlighting a very interesting BMC Biology paper on the discovery of metazoans (creatures in the Animal Kingdom) which live in environments completely devoid of oxygen.

The researchers began their quest by looking at the L’Atalante basin (see below), a so-called deep hypersaline anoxic basin (DHAB) in the Mediterranean Sea. The area in question is over 3 km deep, and is rich in hydrogen sulfide and nearly saturated with salt, the result of which prevents oxygen from less salty waters from mixing into the anoxic (without oxygen) zone.

Now, scientists have known about single-celled bacteria and protozoans capable of living without oxygen for quite some time – and so they were expecting to find tons of those in the anoxic sediments in L’Atalante. What they were hoping to find, however, were multicellular animals capable of living permanently there as well. And find them they did. The researchers, in sifting through the sediment, were able to find three species of living, microscopic (~1 millimeter in size, see below) Loriciferans (themselves a newly discovered, but highly diverse set of creatures).

After verifying that they were alive (and not just dead Loriciferans who sank from another layer of water) and able to do basic things like metabolism without air (and not just air-breathers who were “visiting” the anoxic sediments), the researchers set out to try to determine how these Loriciferans were able to survive:

• without oxygen
• in such a toxic environment (Hydrogen Sulfides are strong reducing agents)
• in an environment as salty as the DHAB

Although the researchers didn’t answer these questions with the level of rigor I would have liked to see, they did make two interesting observations which suggest the sorts of adaptations these creatures evolved to cope:

• Chemical composition of their bodies: The researchers were able to show (see table below) that Loriciferans from the L’Atalante DHAB had higher levels of Magnesium, Silicon, Iron, and Bromine then their non-anoxic cousins, but lower levels of Calcium, Copper, and Zinc. While this wasn’t completely explained, one might hazard a guess that to survive the harsh environment, these Loriciferans evolved new body structure which used different elements to help cope with/shield themselves from the harsh exterior.
  
• No mitochondria, only hydrogenosomes: Almost all oxygen-breathing cells have little organelles in them called mitochondria. Mitochondria are responsible for using oxygen to help convert metabolic products into energy cells can consume. When the researchers applied an electron microscope to the cells of these oxygen-free Loriciferans, they were unable to find any mitochondria. Instead, they found an abundance of hydrogenosome-like structures (below, see all the “H”’s). Hydrogenosomes have previously been found in single-celled creatures which live without oxygen. They use hydrogen, instead of oxygen, to help a cell get energy. This is the first time hydrogenosome-like structures have been found in a multi-cellular creature and probably are a vital adaptation for the Loriciferans in order to let them survive in the DHABs.
  

Found 3 new species of animal life capable of surviving without oxygen? Sounds like a naturalist’s dream come true. But where does one go from here? From my perspective, I’m most interested in two things.

The first is an extension of the studies the researchers conducted on how these creatures have been able to survive. Identifying “hydrogenosome-like organelles” and high-level “chemical/structural adaptations” is cool, but unsatisfying for anyone trained in basic biology. I want to understand how similar those hydrogenosome-like structures are to hydrogenosomes from single-celled creatures. I want to know what genes are responsible for the hydrogenosome-like structures. I want to understand what the different chemical and structural adaptations do!

The second area of investigation is ecological in nature. What exactly does the food web look like down there? Its great that we’ve found single-celled and multi-cellular creatures, but how do they interact?

Paper: Danovaro, Roberto et al. “The first metazoa living in permanently anoxic conditions.” BMC Biology 8:30 (6 Apr 2010) – doi:10.1186/1741-7007-8-30

(Image credit – Gulliver’s Facebook page) (Figures from Additional File 1, Figure 1, Additional File 4, Figure 4 of paper)