The molecule chlorophyll f can directly use long-wavelength light for photosynthesis, extending the range of light living things can harness in this way. The discovery explains how life survives in hostile environments and extends the range of what we should be looking for when searching for life on other worlds. It may even be adapted to assist colonization of Mars.
Plants and bacteria use chlorophyll to harness sunlight to make the molecules they need to live, releasing oxygen in the process. Overwhelmingly this all occurs through chlorophyll a and b, easily the most widely used of this set of related molecules. However, chlorophyll a can only harvest light of wavelengths 700 nanometers or shorter, otherwise known as the “red limit”, and b requires shorter wavelengths still.
Chlorophylls d and f can harvest longer wavelength light. However, Jennifer Morton told IFLScience it appeared, with one exception, that this light was only being used to drive photosynthesis in a very indirect and inefficient way. Morton, a PhD student at the Australian National University, is one of the authors of a paper in Science overturning this belief.
The paper reveals that the cyanobacterium Chroococcidiopsis thermalis uses a mixture of chlorophylls a, f, and d for photosynthesis, with supposedly "accessory" chlorophylls performing an unexpectedly central role. The f and d molecules breach the red limit, directly using 750-nanometer infrared light for photosynthesis.
C. thermalis lives under rocks or partially buried in desert soils where it is not exposed to direct sunlight. There's a good reason for this, since Morton told IFLScience one of her colleagues “learned the hard way normal light is toxic to it.” The vulnerability of chlorophyll f to shorter wavelengths appears to be the reason more species have not adopted it for use in mixed-light circumstances.
The authors studied C. thermalis because the conditions it lives in are some of the closest parallels Earth has to Mars. The work may teach us how to find Martian life. When exposed to more light than it can handle, C. thermalis fluoresces at a different wavelength from organisms that use chlorophyll a, whose characteristic wavelength has been proposed as something we should look for, suggesting we need to seek a wider range of wavelengths.
Moreover, if Mars is conclusively found not to host life, Morton said C. thermalis could help us colonize it.
Not only could this plucky single-celled organism slightly boost the oxygen levels of the Martian atmosphere, it could survive in very low-water environments, and turn the Martian dust into soil more suited to plants. A patient terraforming process could use C. thermalis as a pioneer, clearing the way for plants that could eventually make Mars a suitable home for us.