My human colony on Mars uses gentically modified archea/bacteria to turn dust collected from the surface of the planet into construction material and breathable oxygen. Technicalities of the processing method are not relevant, colonist put dust into machine and machine outputs iron sludge for further refinement with oxygen as a byproduct.

My question is: how much of this is science and how much is it fiction? How far are we in aspect of bioengeneering to be able to create such organisms (to my knowlegde no such archea/bacteria exists in nature). How efficient could be this process in terms of kg of raw materials processed per hour/day? What would be the biology of such organism: should it be fed scraps, exposed to sunlight, could it sustain itself from processing iron-oxide itself?


Now I see a fundamental problem with my idea - unless the organisms arrange the iron into immediately usable structure, the colonists would still need to smelt the sludge at the same temerature as the raw ore, so the whole process didn't contribute anything in refining. Which is fine, maybe the bacteria coats itself with iron shell as sugested by @L.Dutch and fills the prepared form with a porous, iron slabs ready for construction after treating them with hydraulic press.

But assuming that the colonists would actually want to smelt (or rather bake) the resulting substance, is there a chemical compund that is:

  1. soluble in water (I assume the organism wouldn't survive without water),
  2. contains iron,
  3. can be synthesized from iron oxide and
  4. turns into iron under temperature significantly lower than what is required to smelt iron ore or in some other low-energy process
  • 4
    $\begingroup$ Humans, and all animals with red blood, and many (maybe most) bacteria, routinely pick up their iron from iron (III) and iron (II) oxide. The only problem is with outputting the elemental iron; it cannot be ouput atom by atom, because iron is much too reactive, and an isolated iron atom will very quickly find something to combine with. It must be somehow assembled into iron crystals, and those must be assembled into rather large pieces, because iron in tiny pieces self-ignites in air. $\endgroup$
    – AlexP
    Commented Aug 18, 2021 at 10:59
  • $\begingroup$ If the iron can be biologically extracted from rustwater, you might be better off with insects or something that build their hard shells out of iron from the high amount of iron present in their water and then throwing their shells into a furnace once they inevitably die. Or kickstart something like earth's oxygenation event via coral that binds the iron into their structures and expels the waste oxygen. $\endgroup$
    – Lemming
    Commented Dec 8, 2021 at 8:29
  • $\begingroup$ Honestly, involving biology in any way for something as simple as reducing iron seems likely to be far more complicated than it's worth, and probably in the end higher in energy costs. For a low-energy iron extraction/refining process, look at the carbonyl process, which can be applied to impure iron reduced using conventional means or to the iron-nickel meteorites that litter the surface of Mars. The same process can also be applied to nickel using different temperatures. The resulting powders would be far purer than any microbe sludge, and can then be used to produce the desired alloys. $\endgroup$ Commented Dec 9, 2021 at 1:18
  • $\begingroup$ In particular, said sludge will contain large amounts of water, which is energy-intensive to remove and aids in the rapid oxidation of iron, and likely considerable amounts of carbon. One of the main variables that determines the properties of steel is carbon content, and on Earth removing excess carbon involves blowing oxygen through the molten metal. It's also likely getting the iron would involve destroying things like fixed nitrogen and trapping phosphorus/etc in the iron, losing valuable nutrients from the growth cycle. $\endgroup$ Commented Dec 9, 2021 at 1:39

2 Answers 2


If you go from iron oxide to elemental iron in an oxidative environment you are going up on the free energy ladder, while spontaneous processes prefer staying low on that ladder.

This means that the only way to achieve that outcome is putting energy into the process. This is why when smelting iron from iron oxide, one needs to burn coal: it provides the needed energy by burning, and also provide a reducing environment where the reaction can happen.

If you want that to happen in a living organism, there must be some reason for the organism to put energy into the process. Photosynthetic organisms do something similar because they produce energy rich substances (polysaccharides) starting from CO2 and H2O, while releasing oxygen.

Iron doesn't form chain compounds like carbon, so the photosynthetic way seems off. Maybe some bacteria can be engineered to produce an iron shell which is then used as a shield/absorber of EM radiation (on Mars it could be handy).

The shells could be used by your people as starting material for their processes, in a similar way to how diatomite is used on Earth

  • 1
    $\begingroup$ Is there any biological process that produces atomic metal as a (by)product? Maybe I could use that as a basis of what's happening in my case, as many metals share chemical properties with each other. It also feels appriopriate, since genetical engineering is about taking some existing biological process and transplanting it to another organism. $\endgroup$ Commented Aug 18, 2021 at 8:46
  • 2
    $\begingroup$ @ReverentLapwing: Depends on what you mean by a biological process that produces atomic metal. For example, humans (and all animals with red blood) have a mechanism to pick up iron from iron (III) and iron (II) oxide, for use in their haemoglobin. But in this process, the iron atoms are always bound to something, because isolated iron atoms are too chemically reactive and if left alone and uncontrolled will instantly find a partner to combine with. (And remember that even metallic iron is chemically reactive enough to self-ignite in air when in tiny pieces. That's how a fire steel works.) $\endgroup$
    – AlexP
    Commented Aug 18, 2021 at 11:09
  • 1
    $\begingroup$ @ReverentLapwing quite the opposite there are many bacteria that turn atomic iron into rust for energy. $\endgroup$
    – John
    Commented Dec 8, 2021 at 21:39

Very, very doable

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As illustrated in this 1.874 billion year old rock from Michigan, there was a time when Earth's oceans held a high concentration of dissolved iron. It came out of solution when a strange new organism started a biological catastrophe - one which surrounded the Earth in a toxic shroud of a formerly exotic gas known as oxygen. This converted Fe2+ to Fe3+, and the Fe3+ came out of the oceans in vast bands that contain most of the currently mineable iron on the planet.

Fe2+ - iron carbonate - is a very plausible compound to produce on Mars. All you need is iron, water, and carbon dioxide. You might find a workaround for the water.

Reduced iron is also desirable. One commenter noted it is pyrophoric, and it is ... on Earth. Most people would be surprised to hear that a planet covered in one of nature's strongest gaseous oxidizing agents might pose a problem for delicate chemical reactions. Even the natives are prone to inadvertently detonating chemistry labs, and for life forms that evolved in gentle oceans of diethyl ether, the planet is on the Do Not Travel list. Nonetheless, pyrophoric iron is actually made under a CO2 atmosphere, and it is perfectly stable there.

When a region of Mars is doused in melt water, the bacteria will do several things.

  • they need to extract all of the chlorate/perchlorate from the soil to avoid oxidation. They should metabolize this to Cl- and O2. If robots are on the scene they can cover the target area with something to trap the O2 for breathing gas.
  • after the concentration of oxygen has dropped very low, they begin to metabolize the Fe3+ at surfaces into Fe2+ ions (part of FeCO3) in water.
  • As the solution saturates in Fe2+, the bacteria catalyze the conversion of the aqueous iron back to a solid. This can occur full circle by rusting it, or they could convert Fe2+ to solid Fe particles, or they might simply nucleate precipitation of FeCO3. The particles are then periodically collected from the water.

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