Pushing the limit: could cyanobacteria terraform Mars?

Cyanobacteria could be used to render the atmospheres of other planets suitable for human life.

The bacteria that 3.5 billion years ago were largely responsible for the creation of a breathable atmosphere on Earth could be press-ganged into terraforming other planets, research suggests.

A team of biologists and chemists from Australia, the UK, France and Italy has been investigating the ability of cyanobacteria – also known as blue-green algae – to photosynthesise in low-light conditions.

Cyanobacteria are some of the most ancient organisms around, and were responsible, though photosynthesis, for converting the Earth’s early atmosphere of methane, ammonia and other gases into the composition it sustains today.

The photochemistry used by the microbes is pretty much the same as that used by the legion of multicellular plants that subsequently evolved. The process involves the use of red light. Most plants are green because chlorophyll is bad at absorbing energy from that part of the visible light spectrum, and thus reflects it.

Light itself, however, is a critical component for photosynthesis, which is why plants (and suitably equipped bacteria) fail to grow in very dark environments. Just how dark such environments need to be before the process becomes impossible was the focus of the new research.

The team of scientists, which included Elmars Krausz from the Australian National University in Canberra, tested the ability of a cyanobacterial species called Chroococcidiopsis thermalis to photosynthesise in low light.

Previously it had been widely thought that the necessary photochemistry shut down at a light wavelength of 700 nanometres – a point known as the “red limit”.