Researchers at Georgia Tech developed a concept that would make Martian rocket fuel, on Mars, that could be used to launch future astronauts back to Earth. The bioproduction process would use three resources native to the red planet: carbon dioxide, sunlight, and frozen water. It would also include transporting two microbes to Mars: algae and engineered E. coli.
The process begins by ferrying plastic materials to Mars that would be assembled into photobioreactors occupying the size of four football fields. Cyanobacteria would grow in the reactors via photosynthesis (which requires carbon dioxide). Enzymes in a separate reactor would break down the cyanobacteria into sugars, which could be fed to the E. coli to produce the rocket propellant.
The strategy uses 32% less power (but weighs three times more) than the proposed chemically enabled strategy of shipping methane from Earth and producing oxygen via chemical catalysis.