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Self-described "pilot, aerospace engineer, and mad scientist" YouTuber Jack Schneider's video Growing Microbes in Jet Fuel explains that if a layer of water accumulates below jet fuel (due to separation or perhaps other reasons) microbes (bacteria, algae...) can grow in the water and "eat" the fuel:

...since water is denser than jet fuel it sinks to the bottom and creates a layer where microbes can form. Basically the microbes can eat the jet fuel but live in the water and I think that's really interesting. This is a problem in jet fuel tanks because these microbes' byproducts can cause corrosion.

Question: From a microbe's point of view, besides the calorie content of the carbohydrates (hydrocarbons) what are the trace components of jet fuel from which microbes derive nutritional value, and which of their byproducts is causing the fuel tank corrosion?

Just for example: life is based on proteins made of amino acids, and two of these (Methionine and Cysteine) have a sulfur atom. The human body for example (though not a microorganism) is 0.3 % sulfur by weight. So a 70 kg body has about 11 kg of protein, and 200 grams of that is sulfur!

This answer to Why is water-contaminated fuel bad, but water-injection is not? mentions

Water not removed from the tank supports microbial growth.

and this answer to Why aren't "fuel polishing" systems removing water & ice from fuel in aircraft, like in cruising yachts? mentions

...you have ideal conditions for the growth of microbial life in the fuel. This life (technically known as "goo") will, if left to grow rampant, clog your filters to the point where the engine eventually shuts down from lack of fuel.

But neither mention nutritional details nor corrosion.

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  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Aviation Meta, or in Aviation Chat. Comments continuing discussion may be removed. $\endgroup$
    – Jamiec
    May 25, 2023 at 11:38

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The question is complex and really not really aviation-specific. Cars, trucks and especially boats and ships have similar problems.

The energy content of the fuel is well-known and some microorganisms really do have the enzymes to break it down, at least partially.

On the other hand, it is usually not the sulfur what limits the bacterial growth there. Jet fuel contains ~500 to 1000 ppm sulfur. I am sure I (and I am not the only one) have dealt with a diesel tank that had bacteria while sulfur in EU diesel was less than 50ppm for years.

The limiting factors of any life (if the energy is abundant) are usually nitrogen and phosphorus. In contrast with sulfur, these are not considered pollutants and their presence in the fuel is not carefully managed, so bacteria usually have enough of both in the tank.

The inevitable contaminants in the fuel bring the needed microelements.

It looks like the limiting factors for bacterial growth in a fuel tank are the temperature (sub-freezing is not OK for any bacteria) and the limited surface of the water/fuel interface (bacteria needs both and they don't mix) and the availability of oxygen at the interface (usually at the bottom of the tank).

The scarcity of oxygen where these bacteria grow means that their byproduct will be mainly a mix of carboxylic acids (this is how we force some other bacteria to make pickled cucumbers or vinegar for us).

And this is what promotes the corrosion in metals.

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  • $\begingroup$ Thanks for your answer - the most helpful bits seem to be right at the end. As far as "(c)ars, trucks and especially boats and ships have similar problems" goes, they can also have serious problems with ice buildup on the windshields in adverse weather conditions, but that doesn't make questions about what causes and seeds, and what prevents icing any less interesting for Aviation. $\endgroup$
    – uhoh
    May 20, 2023 at 15:52

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