Scientists have discovered a new type of photosynthesis whereby bacteria are able to harvest energy from infrared light. Researchers say their discovery has the potential to alter the search for alien life and allow scientists to engineer more efficient crops.
Led by Imperial College London, the study was published on Thursday in Science.
“The new form of photosynthesis made us rethink what we thought was possible,” said Professor Bill Rutherford, a biochemist at Imperial College London.
“It also changes how we understand the key events at the heart of standard photosynthesis. This is textbook-changing stuff.”
Photosynthesis is the process by which plants and certain bacteria use sunlight to convert carbon dioxide and water into carbohydrates, which they then use as energy sources, and oxygen.
Standard photosynthesis uses a pigment called chlorophyll-a, which gives plants their green colour, to convert light energy into chemical energy. This pigment absorbs visible red light but reflects shorter wavelengths including green, blue and purple light. As a result, chlorophyll-a only allows plants and bacteria to harvest energy from red light.
Because chlorophyll-a is found in all photosynthetic organisms, scientists believed that there was a ‘red limit,’ or a minimum amount of red light energy needed for photosynthesis to occur. The concept of the ‘red limit’ was used in astrobiology to assess whether other planets may have been able to support complex life forms.
In the new study, scientists found that blue-green algae called cyanobacteria are capable of using infrared light to conduct photosynthesis. When the bacteria grow in normal light conditions, they use standard photosynthesis.
However, when cyanobacteria grow in near-infrared light, the bacteria’s chlorophyll-a systems shut down. A different type of chlorophyll called chlorophyll-f then takes over to harvest light.
This process occurs naturally when cyanobacteria grow in shaded conditions, such as “bacterial mats” in Yellowstone National Park in the United States and inside some rocks found on beaches in Australia. The team found that this change also occurs when cyanobacteria are placed in cupboards with infrared LED lights, thereby allowing the organism to photosynthesise in shaded conditions “beyond the red limit.”
“Finding a type of photosynthesis that works beyond the red limit changes our understanding of the energy requirements of photosynthesis,” said co-author Dr Andrea Fantuzzi, from the Department of Life Sciences at Imperial. “This provides insights into light energy use and into mechanisms that protect the systems against damage by light.”
Researchers said their results could one day be used to engineer plants that are more tolerant of fluctuating light conditions. The same technique could also eventually be applied to design life forms suitable for transforming Mars into a more Earth-like environment.
“This might sound like science fiction, but space agencies and private companies around the world are actively trying to turn this aspiration into reality in the not-too-distant future,” said co-author Elmars Krausz, a chemist at the Australian National University.
The discovery also has implications for the search for extra-terrestrial life. The findings suggest that other organisms could be capable of photosynthesising in conditions that were previously thought impossible, potentially expanding the number of planets that may be able to support life.
“It is amazing what is still out there in nature waiting to be discovered,” said lead author Dennis Nürnberg, a microbiologist at Imperial College.