Hydrothermal vents

31 March 2021: Photosynthesis without sunlight

An organism has been found that photosynthesises from light coming from hydrothermal vents 2400 metres below the sea. It is the first photosynthetic organism discovered that does not rely on sunlight.

As reported in a paper pithily titled ‘An obligately photosynthetic bacterial anaerobe from a deep-sea hydrothermal vent’ published in the journal of the Proceedings of the National Academy of Sciences, the green sulphur bacteria was found living near a thermal vent off the coast of Mexico called 9 North.

One of the paper’s authors is Professor Robert Blankenship from Arizona State University’s chemistry and biochemistry department. In an interview with Skip Derra (posted on the university’s website) , Blankenship said the bacteria uses a chlorosome complex which acts like a satellite dish to collect any light it can and transfer it to the organism’s reaction centre where the photosynthesis takes place.

Blankenship also said the discovery was important not just for what it meant for life on earth, but what it means for the search for life outside of Earth.

‘This shows that photosynthesis is something that is not limited only to the very surface of our planet,’ he says. ‘It lets you consider other places where you might find photosynthesis on Earth, as well as on other planets.’

As the original paper’s abstract reflects:

‘The abundance of life on Earth is almost entirely due to biological photosynthesis, which depends on light energy. The source of light in natural habitats has heretofore been thought to be the sun, thus restricting photosynthesis to solar photic environments on the surface of the Earth. If photosynthesis could take place in geothermally illuminated environments, it would increase the diversity of photosynthetic habitats both on Earth and on other worlds that have been proposed to possibly harbor life.’

Something for us science fiction writers to ponder.

Another amazing aspect of this paper is its relative obscurity: the paper was published in June 2005. If not for the heads-up in a recent post by Jerry Coyne on his website Why evolution is true, I doubt I would ever have learned about it.