AUSTRALIA: Scientists discover new chlorophyll

University of Sydney scientists have discovered the first new chlorophyll in over 60 years. Found by accident, the new pigment has been dubbed 'chlorophyll f' and can utilise lower light energy than any other chlorophyll.

It is the fifth known type of chlorophyll and was found in stromatolites - rock-like structures formed by photosynthetic bacteria, called cyanobacteria - in Western Australia's Shark Bay.

Until recently, oxygenic photosynthesis was thought only to occur in light that is visible to human eyes. But in 1996 scientists found a cyanobacterium that could photosynthesise using light just outside the visible spectrum thanks to a modified chlorophyll molecule, named chlorophyll d.

Since this discovery, scientists around the world have been puzzled by how chlorophyll d is able to get enough energy from infrared light for photosynthesis.

But chlorophyll f works at even lower light levels than chlorophyll d. It allows cyanobacteria living deep within stromatolites to photosynthesise using low-energy infrared light, the only light able to penetrate into the stromatolite structure.

Lead author, Dr Min Chen from the University of Sydney, says the new chlorophyll was totally unexpected.

"I was actually looking for chlorophyll d, which we knew could be found in cyanobacteria living in low light conditions. I thought that stromatolites would be a good place to look, since the bacteria in the middle of the structures don't get as much light as those on the edge," said Chen.

But high performance liquid chromatography of a cultured sample revealed the new chlorophyll. And testing revealed the new chlorophyll could absorb much longer wavelengths of light than any other known chlorophyll.

"Discovering this new chlorophyll has completely overturned the traditional notion that photosynthesis needs high energy light," Chen said.

"It is amazing that this new molecule, with a simple change to its chemical structure, can absorb extremely low energy light. This means that photosynthetic organisms can utilise a much larger portion of the solar spectrum than we previously thought and that the efficiency of photosynthesis is much greater than we ever imagined."

Chen says chlorophyll f could have applications for industries such as plant biotechnology and bioenergy.

"For us, the next challenge is to work out the function of this new chlorophyll in photosynthesis," she says.

"Is its job to capture additional red light and pass it on to another chlorophyll, like chlorophyll a, in the reaction centre for photosynthesis?

"Or is it the only chlorophyll responsible for photosynthesis in the cyanobacterium? And if it is, then we will be speechless wondering how this molecule can get enough energy from infrared light to make oxygen from water."

The research was published in the journal Science.