A small California research group says it has made the first microbe built for Mars. Outside experts say it is a useful lab result, not a way to bring the planet to life.

Pioneer Labs, a nonprofit startup in Emeryville, took a common soil bacterium and slowly exposed it to tougher and tougher Mars-like conditions. The evolved strain, called sPL.001, can grow on lab-made versions of Martian dirt, water and air and turn them into bioplastic, a material that could feed 3D printers to build shelters, Space.com reported.

"Mars has all the raw materials for life in abundance," CEO Erika DeBenedictis said. She calls the microbe the first of five organisms her team thinks are needed to "green" Mars.

There are big limits. The microbe cannot live in the open on Mars. It must grow inside a heated, stirred tank called a bioreactor, shielded from cold, radiation and the thin air. It also needs nitrogen delivered in processed form, and it cannot make its own food. The team says those limits make it safe, because it would die if it escaped.

And the tests used simulated Martian soil, not the real thing. "Simulated Mars isn't actual Mars," DeBenedictis said.

Scientific American asked several researchers for their views. Most were fairly positive about the science, but some pushed back on the terraforming talk. NASA planetary scientist Chris McKay said the microbe is "not for terraforming Mars, it's for making feedstock for 3D-printed houses." A Newcastle University researcher called the announcement "rather over the top."

Others see promise in making building materials from local resources instead of shipping everything from Earth. Moving any living microbe to Mars would also need approval under international rules meant to keep other worlds from being contaminated.

The work is described in preprints, early papers that have not yet been reviewed by other scientists.

What we know: The microbe makes bioplastic from simulated Mars materials in a lab.
What we don't: Whether it would work with real Martian soil.