Chlorophyll in ancient bacteria: biofuel source?
Scientists have discovered a new type of chlorophyll in ancient Australian bacteria that could lead to new sources of bio-energy.
Over the past 60 years, scientists have known of four types of chlorophyll used by plants to harvest light and convert it into chemical energy in the process called photosynthesis.
In a report published Friday in the journal Science, researchers said they found a fifth type of chlorophyll in a colony of bacteria in stromatolites at Shark Bay on the Western Australian coast.
Often referred to as living fossils, stromatolites are layered structures of mostly cyanobacteria — blue-green bacteria — living in shallow water.
Associate professor Robert Willows of Sydney's Macquarie University was part of the team that made the discovery.
Willows says the new pigment named "chlorophyll F" absorbs a far redder part of the spectrum than other types of chlorophyll, extending into the near-infrared range.
"That makes this new discovery the reddest chlorophyll to be identified so far," he says. "It was found deeper in the stromatolite structure, which explains why it needs the longer wavelengths of light for photosynthesis."
Other types of chlorophyll include chlorophyll A, (thought to have been the first to have developed) as well as types B, C and D.
Willows says these types of chlorophyll all absorb light in the blue region of the spectrum, which is why they're green, a combination of blue and yellow.
"Chlorophyll D, which is what we were looking for when we made the discovery, also absorbs light in the infrared, but not as far as chlorophyll F," says Willows.
"There was also a chlorophyll E, described back in the 1950s in Russia, which may have been the same as the newly discovered chlorophyll F, but wasn't characterized, so we can't be sure."
Willows says chlorophyll F is right on the edge of what's possible in terms of using light to make oxygen by photosynthesis.
"Light at longer wavelengths can't split water to make oxygen," he says. "There are other bacteria chlorophylls that do absorb further into the infrared, but they can't make oxygen and so haven't been successfully used in plants."
Willows says the discovery could provide new ways to help crop plants and algae (used to create biofuel) grow more efficiently by making better use of available light.
Willows says cholorophyll F may even have helped oxygenate the Earth's atmosphere.
"The bacteria producing chlorophyll F look indistinguishable from stromatolite bacteria fossils found in the Western Australian Pilbara region," he says. "These have been dated back some three billion years and represent some of the Earth's earliest life forms."