Anaerobic Animals Discovered on Sea Floor

ResearchBlogging.orgThis is pretty neat: scientists have apparently discovered the first example of truly anaerobic animal life (i.e. an animal that can survive in the absence of oxygen). This isn't some sort of fuzzy critter, though; instead, these are tiny (less than 1 mm in length) animals that were found on the floor of the Mediterranean Sea. The animals belong to the phylum Loricifera (see illustration below). Significantly, these animals lack mitochondria, the sub-cellular organelles where oxygen is employed to produce ATP in aerobic (oxygen-dependent) life.

i-6ad141a6385b1316c5975202949bc557-loricifera.gifYou can check out the original paper by Danovaro et al. (and two accompanying commentary articles) at BMC Biology:

Danovaro, R., Dell'Anno, A., Pusceddu, A., Gambi, C., Heiner, I., & Kristensen, R. (2010). The first metazoa living in permanently anoxic conditions BMC Biology, 8 (1) DOI: 10.1186/1741-7007-8-30

Levin, L. (2010). Anaerobic Metazoans: No longer an oxymoron BMC Biology, 8 (1) DOI: 10.1186/1741-7007-8-31

Mentel, M., & Martin, W. (2010). Anaerobic animals from an ancient, anoxic ecological niche BMC Biology, 8 (1) DOI: 10.1186/1741-7007-8-32

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Very Interesting!

"Life will find a way". Dr. Ian Malcomb

So are they primitively anaerobic and lacking of mitochondria, or like many parasitic organism, have they adapted to this niche from an aerobic background via loss of mitochondria etc.?

As far as I can tell, these organisms are totally anaerobic, although they would have presumably evolved from aerobic organisms originally.

So they lack mitochondria?

Apparently they have Hydrogenosome, which are thought to be derived from mitochondria.

Thanks, Razib; I'm doing my best. I guess I've just been getting "distracted" by a lot of real world things over the last few months, and the poor blog has certainly suffered.

Apparently they have Hydrogenosome, which are thought to be derived from mitochondria.

Derived multiple times, at least semi-independently. There are also several cases of facultatively anaerobic mitochondria. See my (very) recent post on this subject and references therein, especially:

Mitochondria as we donât know them by Aloysius G.M. Tielens, Carmen Rotte, Jaap J. van Hellemond, and William Martin

How do these critters get the oxygen they need to synthesize collagen?

Or does there small size allow them to get around this?

I believe that all animals synthesize collagen (but someone please correct me if I'm wrong). That's a moot point, though, because oxygen is found in all biological molecules, and life could not survive without it. Even a molecule of water is made up of one atom of oxygen and two atoms of hydrogen. So, these organisms could get their oxygen from water, but also from any other organic material they digested. In the post--and when people talk about anaerobic versus aerobic organisms--we're talking about the necessity of the incorporation of molecular oxygen (O2) specifically in producing ATP.

It had been my understanding that the synthesis of collagen requires molecular oxygen (not just atomic oxygen bound to other organic molecules), and that this has in fact been proposed as a hypothesis for why multicellular animals appeared when they did in the fossil record (ie they needed collagen to assemble their bodies and could not do so until atmosphere O2 had risen to a high enough level).

It had also been my understanding that the same is true for lignin for plants - the cross linking that gives lignin its strength requires molecular oxygen.

In other words, molecular oxygen is needed by multicellular life for much more than just ATP production.

Thus my question: if the above is true, how do these animals synthesize their collagen?

As a clarification of the above, molecular oxygen, as I understand it, is necessary for the post-transcriptional hydroxylation of proline to hydroxyproline - ie the oxygen in the hydroxyproline does not come from water, but is added from an O2 molecule by an oxygenase enzyme.

The hydroxyprolines are critical for collagen strength. Thus in the complete absence of O2, animals bodies simply would not be able to hold together beyond a certain size (hence my first question about whether or not the small size gets around the problem).

The level of O2 needed is actually much lower than current atmospheric O2 in aerobic environments, and may be low enough that it could be found even in environments that would be considered to be hypoxic. But the post seemed to suggest that these animals lived in a completely anoxic environment - there is no O2 at all? If which case, how do these animals synthesize collagen?

Ah, I see: molecular oxygen is required for the hydroxylation of proline residues in collagen. So, now I see what you mean. I don't know the answer to your question, but I could envision four scenarios here:

1. These animals don't express collagen.
2. These animal express collagen, but it doesn't contain hydroxyproline.
3. These animals hydroxylate proline by some alternative means.
4. There is a very small residual amount of oxygen still present in their environment, and this can be incorporated in the hydroxylation of proline.

Without knowing anything more, I would just guess (and please keep in mind that this is just a wild guess), that scenarios #2 or #4 are the most likely. Proline hydroxylation occurs after collagen is synthesized, and it is my understanding that it might not be totally necessary for the formation of collagen--but it just provides generally needed additional stability.

Hopefully someone with more expertise can resolve this question.

Oops, it looks like our posts crossed one another there (I wrote mine before I saw yours). It looks like we're both thinking along the same lines now, though.

I don't know how much oxygen is actually present there. The authors just refer to their natural environment as "permanently anoxic", though they also note that these deep sea environments in general are characterized by an oxygen concentration of < 0.5 mM (although it must be much less than that, since I don't think that 0.5 mM is an incredibly low oxygen concentration). They also show that under anoxic laboratory conditions, these organisms are still viable.

Yeah, I'm thinking it is possible that even environments considered to be anoxic might have some tiny level of O2, which might be enough.