Sulphur breathers

Anoxic ocean beds were found to harbour multicellular life  

By Tiasa Adhya
Published: Wednesday 30 June 2010

THE oceans are as vast and unexplored as the universe. They churn up something new everyday. The most recent discovery is a multicellular organism that can live in the darkest depths without oxygen.

During the last 10 years, marine scientist Roberto Danovaro and colleagues at the Marche Polytechnic University in Italy conducted three oceanographic expeditions to search for living fauna in the sediments of the Mediterranean sea. Salt concentration at these depths is 350 g/litre. Due to its heavy density, the salt-saturated water does not mix with waters above. As a consequence, this environment has been devoid of oxygen for 50,000 years. It is also filled with toxic sulphide. Such harsh conditions, where a higher animal can smell its death, harbour unicellular bacteria that make food out of the sulphur. That this ecological niche can also support multicellular life is a surprise.

The team found three new species with bodies enclosed in a protective external shell or lorica. “The animals were put under Loricifera, the most recently discovered animal phylum (1983),” said Antonio Pusceddu, an author of the study.

“This find might seem impossible to some, after all one often reads animals have an absolute requirement for oxygen or that sulphide is poisonous,” said Marek Mentel, biochemist from Comenius University in Slovakia.

Animals use oxygen to break down glucose in organelles called mitochondria and produce energy. The new species possess structures called hydrogenosomes. Hydrogenosomes can do in the anoxic environment what mitochondria does in the presence of oxygen. This find led to two schools of thought: some believe Loricifera adapted to the anoxic environment by evolving hydrogenosomes; others believe the organelles are ancient remnants.

William Martin, researcher from the University of Dusseldorf in Germany, said they are remnants from the time when the Earth’s oceans were anoxic and sulphidic—roughly 1.8 billion years to 560 million years ago. That was when eukaryotes—multicellular organisms—evolved and diversified. “Hence it should hardly be surprising that the anaerobic lifestyle is widespread among eukaryotic lineages,” he added.

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