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I'm trying to create a hard sci-fi book where the main character uses biophotovoltaic cells to power electricity, my question is: How can I make my cyanobacteria last at least a year inside an hydrogel, could this be possible without feeding it? I've seen some papers regarding biophotovoltaic cells but I'm sure none of them mentions how long they can the bacteria last inside the hydrogel...

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  • $\begingroup$ Welcome to worldbuilding. Please read our help center to understand what we expect from a good question. It's a bit hard to answer without any further detail on this bacteria and the substrate $\endgroup$
    – L.Dutch
    Oct 20, 2022 at 19:48
  • $\begingroup$ What is a "biophotovoltaic cells"? $\endgroup$
    – Daron
    Oct 20, 2022 at 19:52
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    $\begingroup$ researchgate.net/publication/… apparently this one lasted about a month. I think for story purposes a year could be fine. Perhaps they go dormant as @Daron suggested or the hydrogel itself becomes consumable over time. It seems that if you use combinations of microbes you have options, although some types are mobile and may try to escape! $\endgroup$
    – UVphoton
    Oct 20, 2022 at 22:30

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Dormant State

When there are no nutrients around it is common for microbes to enter a dormant state where they can remain for months or years. If you don't feed the microbes, they should hibernate like this.

The fact that microbes can go dormant sounds like it would be folklore to microbe people. Perhaps some friendly microbe people can verify that for me? This paper says some cyanobacteria do this.

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Cyanobacteria eat CO2.

So if your hydrogel is in contiguity with the atmosphere the atmosphere will diffuse in and feed them the carbon they need. They can also get their nitrogen from the atmosophere; cyanobacteria can fix nitrogen. I think it is not such a stretch to assert that other inorganic nutrients (e.g. phosphate, metals) are present in the hydrogen and also made available by cyanobacteria that die and break down.

I think the issue for the hydrogel in contiguity with the atmosphere over a year will be dessication - it will dry out. You could have your hydrogen in contiguity with a large volume of humid CO2 and N2 that would be enough "food" for the year and which would not allow dessication.


I should add that actually cyanobacteria "eat" photons; they are of course photosynthetic. Your bacteria would be fed by a light source. In some places you can periodically have that for free.

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Sporulation is a last resort

Willk already pointed out that they will be fine as long as they have enough CO2, water, light and nutrients to keep going and Daron had a good idea with the dormant state. When conditions get bad, bacteria often resort to sporulation. This is a dormant state that makes bacteria incredibly resistant to all kinds of difficult environmental conditions (radiation, poison, drought, etc.). It is currently not known whether there is an upper limit to the duration of this state, but they can most likely survive at least multiple millennia if they have to.

This means that your solar cell will stop working as soon as the bacteria have troubles with supply, but some of them will most likely survive indefinitely and can repopulate the cell in a short amount of time as soon as conditions get better.

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