The first Mars travelers will have to grow their own food on the red planet. It may require that they bring along a hefty load of bacteria in addition to their green fingers.

About 250 days. How long does it take to fly from Earth to Mars. Doing some shopping on earth is therefore not an option for future Mars colonists. Future Mars travelers who nevertheless want to eat a bit varied and healthy will have to plant their own vegetable garden on Mars. That is not impossible; countless experiments – including at Wageningen University – have already shown that it is possible to grow certain crops on the Martian soil with a little effort.

Nitrogen

At the same time, the Martian soil is not as fertile as the soil here on Earth. For example, it lacks various nutrients that are essential for plants, such as nitrogen. But we can do something about that, say American researchers. Through experiments they show that it is possible to make the soil more fertile by enriching it with certain bacteria.

Using bacteria to help plants grow: that is of course not a new idea. Terrestrial plants receive massive help from bacteria. “Plants need nitrogen,” researcher Franklin Harris explains when asked. “Fortunately, the Earth’s atmosphere consists for the most part of nitrogen.” The problem is that plants can’t do anything with atmospheric nitrogen. Fortunately, there are bacteria that convert atmospheric nitrogen into a form of nitrogen that the plant can handle. “These bacteria live in nodules in the roots of the plant. The plant feeds the bacteria and the bacteria extract nitrogen from the atmosphere and change it so that the plant can use it. A small percentage of the nitrogen that is so adjusted leaches from the roots into the soil. And so the bacteria also make the soil more fertile; they add nitrogen from the atmosphere to the plant and soil.”

Big difference

On Earth, the collaboration between bacteria and plants is an unparalleled success. But can the bacteria also help on Mars? Harris and colleagues have put it to the test. They took simulated Mars soil and put clovers in it. Some of the clovers were provided with a microbe – Sinorhizobium meliloti – which lives in clover roots here on earth and supplies them with nitrogen. The result was impressive; clovers that received help from bacteria developed 75 percent more roots and leaves than the clovers that stood alone. “Just looking at it, you could clearly see which plants were and which were not enriched with the bacteria,” Harris said. “The plants without S. meliloti Not only were they smaller, but their leaves also discolored – often indicative of a nitrogen deficiency.”

Nitrogen does not leak on Mars

What the researchers did notice was that the soil around the bacteria-enriched clover plants did not have an elevated nitrogen level. Where the nitrogen processed by bacteria here on earth sometimes wants to leak out of the roots and also makes the surrounding soil more fertile, this does not happen in the Martian soil. “It could mean that there are differences between how well or at what speed nitrogen is fixed (taken from the air by bacteria and adapted for use by the plant, ed.). But it could also indicate that nitrogen moves through the system in a different way or that the plants themselves are using more nitrogen. It’s hard to say whether that’s good or bad news for plant health. But even if roots in Martian soil are not able to release nitrogen and thus contribute to soil fertility, we know that the plants still benefit from the symbiosis (the cooperation with bacteria, red .), because they have more nitrogen. So we can use that knowledge when we think about solutions for growing food on Mars.”

Bacteria on Mars

Bacteria can also help plants to grow on Mars. Does that mean that in addition to all kinds of seeds, astronauts also have to carry quite a few bacteria with them to Mars? “It’s hard to say without additional research,” Harris said. “We do not yet fully understand how the lack of (here on earth, ed.) naturally occurring bacteria, primordial bacteria and fungi affects the growth of plants and therefore also the yield of crops.” That said, it’s certainly not inconceivable that future Mars travelers will have microscopic companions. “I think that, given the results of this research, we can conclude that plants also grow better with their symbiotes in Martian soil. An alternative is to use fertilizer to meet the nitrogen needs of plants.” But when you consider that the cost of launching increases enormously with every extra kilogram of weight, it is not so attractive to carry fertilizer with you. “It is much cheaper to use bacteria instead of fertilizer, because then you only need a few bacteria and the means to grow them. After all, they multiply themselves.”

Planetary Protection

Still, with a view to planetary protection, you may also be a bit hesitant to take bacteria to Mars. Because what if they colonize the red planet at the expense of any native bacteria? “There is always a risk and it would be terrible and embarrassing if we were to ruin our ability to discover new life by introducing an invasive microbe.” But that does not automatically mean that we should leave the bacteria at home. For example, Harris points out that the bacteria used in the experiments are classified as ‘non-competitive’. “That means they are unlikely to outcompete local bacteria. “In addition, given that the plants have to be grown in an enclosed space, it shouldn’t be difficult to keep the bacteria inside and prevent contamination. Especially because Mars is an extremely harsh environment for terrestrial life. With temperatures as low as -60 degrees Celsius, (toxic, ed.) perchlorates on the Martian surface and large amounts of radiation, it is difficult for any bacteria to spread and become a problem. That said, of course, when it comes to controlling our bacteria, we can’t just rely on the properties of the Martian landscape.” Ultimately, we will also have to take active measures to prevent the bacteria from ‘escaping’ and settling elsewhere on Mars. What those measures will then look like is something that needs to be further investigated in the future.

The first manned missions to Mars may still be far away; it’s good to start thinking now about the challenges the early Mars travelers may face. A disappointing harvest is such a challenge. And bacteria may help prevent Mars travelers from going hungry. “I would say the main implication of this research is that we can use farming methods that we use here on Earth – with some adjustments – to grow things on Mars as well.” And with a bit of luck, it will lead to new insights that we can also use here on earth – where the cultivation of crops does not always go smoothly.