No O2 please, we're multicellular

A long standing piece of received wisdom bit the dust this week. All multicellular animal life on Earth had been thought to require oxygen to survive - be it atmospheric or dissolved in water. Danovaro et al. now report the discovery of three species of multicellular life (metazoans) living happily in the oxygen devoid, highly salty, muck at the bottom of the Mediterranean. They belong to a family known as Loricifera, about 1mm in size.

Unlike creatures like us, these tiny organisms forgo cellular mitochondria (the energy power plants of most multi-cellular life) for other molecular structures than can produce energy carrying molecules without the need for oxygen. This is a trick that had been thought to be the sole province of single-celled microbial life - like bacteria and archaea. In fact, just as the mitochondria are the end result of endosymbiosis - the assimilation of a previously symbiotic organism - it seems that the same is true here, a molecular tool from a useful microbe has become part of the genetic makeup of these teeny animals.

The standard lore - at least the one I generally spout - is that multi-cellular life arose on Earth because the increasingly oxygenated atmosphere 1-2 billion years ago enabled life to exploit a new and rich, energetically favorable biochemistry. What would be really interesting now is to figure out whether these sub-Med creatures are ancient or a later 'backwards' adaptation of multi-cellular life ?

Clearly as well, for astrobiology, this raises some fascinating questions. One that immediately springs to mind is the issue of whether or not a subsurface ocean on Europa could sustain complex life. People have debated how oxygen might find its way into the liquid interior of the moon, but it's tricky without invoking mechanisms that can seem a bit contrived. So, if multi-cellular life can function using a different biochemical trick to do without oxygen I'd say that the bets might need to be revised. [ZPHM5ZUP82SE]