I made an organism called the Skarlix for a art/xenobiology project called Sagan 4.

The Skarlix is a eukaryotic, somewhat amoeba-like organism that "eats" various metal compounds and "breathes" (oxidizes) hydrogen (e.g., in the form of hydrogen gas, unless other compounds are more plausible). Its metabolism is based partly on the brief Wikipedia description for knallgas bacteria. However, I think I messed up at some point in its description, probably because I didn't understand the difference between "eating" and "breathing" at the molecular level.

I think "eating", on the cellular level, means gaining energy for growth. Is there a way to make it gain mass by eating metal compounds of some sort, but use hydrogen in roughly the same ways human cells use oxygen? If not, is there a way to make it need very little to no oxygen, "breathe" an alternative element or chemical, and rely on metal in sediment?

More information: This is a free-living, somewhat amoeba-like (in shape) simple eukaryote which lives in sediment in the ocean. While I don't need to go into detail on electron donors and acceptors in its description, I do need to know whether this metabolic combination is even plausible. If not, I should alter it. Ideally, any alteration wouldn't prohibit its descendants from plausibly living in the guts of a creature that consumes very iron-rich foodstuffs, or within the blood of a creature with manganese-based blood.

The Skarlix was created in an era equivalent to the Precambrian/Early Cambrian on its planet, after a big extinction event. Since it was created, many microbes have developed, probably including those that make hydrogen compounds. While pairing it with a microbe that consumes hydrogen makes sense, that's going much too far into its timeline to be plausible. As for its diet of "metals", that was left unspecified in the description. Early lithotrophs in the Sagan 4 project didn't have their exact diets specified, presumably so even people unfamiliar with lithotrophic biochemistry could stock the planet with lithotrophs. Any metal which makes sense in this situation is appropriate, except copper, which I specified is too poisonous to it. (not sure about the plausibility of that, but it's stuck there. Another organism was later developed which ate copper, an under-utilized resource because the Skarlix wouldn't eat it.)

  • $\begingroup$ I've added a couple of tags which should make the question pop-up in the feed of those who can help. Feel free to revert the edit if you feel it's appropriate. Take the tour, and when you fancy you can browse the help center to see how we work. Meantime - welcome to the site. $\endgroup$ Dec 11, 2019 at 14:36
  • $\begingroup$ Why? Yes, you can make up things that are close to what you want. Why do you need such great details in your world down to the basics of life if you are obviously not an expert? Don't make things hard for you. Anyhow, there are a couple of options, please elaborate where you want to go with this. Why do you need this lifeform? What kind of metals? What exactly do you mean by metal anyways? What does this microbe do that is relevant to your plot? Btw, you might be better off with a symbiosis. Make one microbe eat metal and produce hydrogen and another one consuming it. That's more reasonable $\endgroup$
    – Raditz_35
    Dec 11, 2019 at 14:45
  • $\begingroup$ Metal Metal or an element from metal part of periodic table? $\endgroup$ Dec 11, 2019 at 14:51
  • $\begingroup$ I'm not sure what you mean by "metal metal", but I went to specify what I meant in the description. Any metal, as per the periodic table, is fine for my purposes. (except copper.) $\endgroup$ Dec 11, 2019 at 15:07
  • $\begingroup$ You've added more detail but not really answered my questions. Where do you want to go with this? Why go into molecular Detail if you have no plan to go somewhere? Anyone with any education in chemistry would come up with a solution very quickly which means you don't know the field very well. It's not good world building if you do things just because even though you don't know how $\endgroup$
    – Raditz_35
    Dec 11, 2019 at 15:49

2 Answers 2


We breath oxygen primarily because it's highly electronegative and hence works as an electron attractor in the electron transport chain system of atp production. This is a rather specific metabolic system and it's far from foundational, tons and tons of bacteria don't have this type of energy system, (in fact even humans have several others in addition to this one!)

In fact, there are really existing earth bacteria that use metals in their metabolic systems, and frequently absorb environmental sulfur or oxygen (or probably other things, maybe not hydrogen though, H2 is very stable) as a way of breaking down metals into more usable forms.

Really you've just got to decide how detailed you want to get with this. Fully describing the chemistry of a totally novel metabolic cycle seems like it would be pretty hard, certainly it's above my pay grade. At the same time, I wouldn't doubt for a second the plausibility of "a Bacteria which metabolizes [some metal] by absorbing [some gas] in a low oxygen atmosphere". Hell, there's probably one on Earth that fits the bill.

To fill out this response with some more specific information, you can look at a couple of the following things:

1: Sulfate Reducing Microorganisms: https://en.wikipedia.org/wiki/Sulfate-reducing_microorganisms -- these are examples of bacteria that "breath" sulfates instead of oxygen to power their respiration. In other words, they use sulfates as the final electron acceptor in their electron transport chain. These are prokaryotes however. Some of these are called Chemolithoheterotrophs, which is the class of bacteria here that reduces inorganic material rather than organic material, which is kind of the thing you are looking for. 2. https://microbewiki.kenyon.edu/index.php/Dissimilatory_metal_reduction Here is a short article talking about how microbes can "consume" metals to produce energy. In your post you said you wanted the microbe to consume metals to gain mass, but keep in mind that for the most part the mass of a single microbe is naturally limited by scaling factor difference between volume (~mass) and surface area (~max "eating" rate), so for a colony of bacteria to gain mass by consuming metals you just need a metal to be "consumed" (usually this means corroded or oxidized) as part of the colony's metabolic process.

I'd hoped to find an example of a specific Earth bacteria fitting your criterion, but I wasn't able. However, nothing about what you're asking for is too 'out of this world' (yuk-yuk) certainly the individual elements you're asking for are well represented and pretty well understood.


Let's take a look at what the living things we know do. They breath in oxygen, combine it with carbon from their diet, then exhale carbon dioxide. The chemical reaction of 2 parts of oxygen with 1 part of carbon is an exothermic one. Which means that the process releases energy and that is why we are able to rely on it in the first place.

Now let's take a look at what you want to accomplish. A microbe that uses some metal + h2 to create a new molecule and gain energy in that process.

So the question can be rephrased to: Is there a metal that when combined with h2 produces an exothermic reaction?

Now unfortunately my chemistry knowledge is miserable. But maybe someone else can come up with an exothermic reaction of h2 and some metal.

  • $\begingroup$ Metal hydrides do exist, so there's definitely an energy release pathway there $\endgroup$
    – nzaman
    Dec 11, 2019 at 14:48
  • $\begingroup$ Iron hydrides look unpromising. en.wikipedia.org/wiki/Iron_hydride They are not particularly stable, or stable only at huge pressures and weird temperatures. Tends to suggest they are not good sources of energy. $\endgroup$
    – puppetsock
    Dec 11, 2019 at 14:54
  • $\begingroup$ Nickel looks a bit more promising. en.wikipedia.org/wiki/Metal_hydride_fuel_cell If you can make batteries out of it, presumably it can contain energy. $\endgroup$
    – puppetsock
    Dec 11, 2019 at 14:56
  • $\begingroup$ Making metal hydrides barely make sense, mainly because i'm sure that the op wouldn't know what to do with them. That's also where you lose 99.9% of your audience. They are not a good building block for life. It should be best to separate the hydrogen and metal thing. There doesn't need to be a literal reaction between both. Consuming hydrogen = energy and interesting compounds. Consuming metal = energy. Why not do both at the same time $\endgroup$
    – Raditz_35
    Dec 11, 2019 at 15:50
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    $\begingroup$ @puppetsockreinstateMonica yes you are right. well i will just not answer anymore when i don't have the time to research it completely. Which i will probably not be motivated to do so... doesn't matter. $\endgroup$ Dec 12, 2019 at 13:22

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