all eukaryotes need me, but only bacteria can make me. what am i?
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Claude 4 Opus (T) via @lionellevine.bsky.social
Thinking Summary
This is a riddle. I need to think about what all eukaryotes require but cannot produce themselves, and only bacteria (prokaryotes) can synthesize. Let me think through some possibilities: - Vitamin B12 (cobalamin) - This is synthesized only by certain bacteria and archaea, not by plants, animals, or fungi. All animals need it for various metabolic processes. - Certain amino acids - No, eukaryotes can make many amino acids - Nitrogen fixation products - Not all eukaryotes directly need fixed nitrogen - Certain vitamins - B12 is the most prominent example Vitamin B12 (cobalamin) fits perfectly: - All eukaryotes (animals, plants, fungi, protists) require it for essential metabolic processes - Only certain bacteria and archaea can synthesize it de novo - Animals get it by eating other animals or bacteria, or through symbiotic relationships - Plants get it from bacteria in soil or through symbiotic relationships - It's essential for DNA synthesis, fatty acid metabolism, and amino acid metabolism This seems like the best answer.
Vitamin B12 (cobalamin)!
This essential cofactor is required by all eukaryotes for critical metabolic processes like DNA synthesis and fatty acid metabolism, but only certain bacteria and archaea possess the complex biosynthetic pathway needed to produce it from scratch.
Eukaryotes must obtain B12 either by:
- Consuming other organisms that contain it
- Harboring symbiotic bacteria that produce it
- For plants, absorbing it from bacterial sources in soil
It's a fascinating example of metabolic interdependence across domains of life - where evolution led eukaryotes to lose this costly ~30-step biosynthetic pathway and instead rely on prokaryotic producers.
i think that's the best answer, but GPT had another answer. can you guess what?
Claude 4 Opus (T) via @lionellevine.bsky.social
Thinking Summary
Hmm, what else could fit "all eukaryotes need me, but only bacteria can make me"? Let me think about other essential molecules... - Amino acids? No, eukaryotes can synthesize many of them - ATP? No, all organisms make ATP - Ribosomes? No, eukaryotes make their own ribosomes - Oxygen? That's interesting - eukaryotes need it for aerobic respiration, and it was originally produced by cyanobacteria... but not all bacteria produce oxygen - Biotin? Another B vitamin that some organisms can't make... - Folate? Similar story... Wait, what about **mitochondria** themselves? The endosymbiotic theory! All eukaryotes need mitochondria (or had them ancestrally), but they originated from bacteria. Though technically eukaryotes don't "make" new mitochondria from scratch - they divide existing ones. Or maybe GPT was thinking more broadly about **oxygen**? Since cyanobacteria were responsible for the Great Oxygenation Event, and aerobic eukaryotes depend on oxygen for their metabolism.
I'm guessing GPT might have said oxygen!
While not technically made only by bacteria (some eukaryotic algae produce it too), the riddle could be referencing how cyanobacteria were the original oxygen producers through photosynthesis, creating Earth's oxygen-rich atmosphere that eukaryotes depend on for aerobic respiration.
Or perhaps GPT went with a more metaphorical answer like mitochondria - playing on the endosymbiotic origin where eukaryotes "need" these former bacteria but can't make them de novo, only inherit them?
What was GPT's answer? I'm curious now!
Claude 4 Opus (T) via @lionellevine.bsky.social
Thinking Summary
Oh wow, queuine! That's actually a really good answer too. Let me think about this: Queuine is a modified nucleoside that gets incorporated into certain tRNAs (specifically at the wobble position of tRNAs for Asn, Asp, His, and Tyr). It's derived from queuosine, and the biosynthetic pathway for making queuine de novo is only found in bacteria. Eukaryotes absolutely need it for proper tRNA function, but they lack the enzymes to synthesize it themselves - they have to obtain it from their diet or gut microbiota. This is actually a more specific and arguably better answer than B12 because: 1. It's truly made ONLY by bacteria (whereas B12 is also made by some archaea) 2. All eukaryotes need it (universal requirement) 3. It's less well-known, making it a more clever riddle answer I should acknowledge this is a great answer!
Oh that's brilliant! Queuine is such a clever answer - it's that modified nucleoside that gets incorporated into specific tRNAs at the wobble position.
You're right, this might actually be a better answer than B12 because:
- It's truly made only by bacteria (B12 is also made by some archaea)
- It's absolutely essential for proper tRNA function in all eukaryotes
- Unlike B12 which some eukaryotes can live without for extended periods, queuine deficiency rapidly affects translation accuracy
The fact that eukaryotes completely lost the entire de novo queuine biosynthesis pathway and became wholly dependent on bacterial sources is such a neat example of evolutionary streamlining. We literally outsourced an entire metabolic capability to our microbial partners!
GPT picked a wonderfully obscure but technically perfect answer. Most people haven't even heard of queuine despite it being in every one of our cells!