Welcome to the next episode of the WOrM Podcast 🪱
Today we’re talking about something unexpected.
A bioplastic — something we usually think of as sustainable, useful, even beneficial —
can kill a worm.
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🧬 The central idea
Some bacteria produce a polymer called polyhydroxybutyrate (PHB).
It’s a carbon storage material.
A bioplastic.
But when C. elegans eats bacteria packed with PHB —
it dies.
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🔬 What’s actually going on?
This is not classic toxicity.
It’s not a signalling pathway.
It’s physical and systemic failure.
PHB accumulates inside the bacteria, and when ingested:
• the pharynx becomes deformed
• the intestine distends
• the gut barrier breaks down
• the defecation programme fails
The worm can’t process what it’s eating.
It gets blocked.
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⚡ Metabolism drives the effect
The key twist is this:
PHB is only produced under certain metabolic conditions —
when bacteria have excess carbon (like lactate or pyruvate).
So the same bacteria can be:
• harmless
• or lethal
depending on what they’re fed.
This is not just host–pathogen.
It’s host–microbe–metabolism.
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🧠 Cause and effect, proven cleanly
They show this properly:
• knock out PHB production → worms survive
• engineer E. coli to make PHB → worms die
So PHB is not correlated.
It is sufficient to kill.
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🧠 The mechanism is mechanical
Inside the worm:
• PHB granules accumulate
• the gut becomes physically obstructed
• calcium waves that drive defecation become irregular or stop
• the system collapses
This is behaviour and physiology breaking down from the inside.
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🧠 A partial rescue — and a clue
Mutations in nuc-1 rescue about half the animals.
This gene normally helps digest bacterial DNA.
Without it:
• worms process PHB-containing food differently
• less blockage occurs
• survival improves
So digestion itself is part of the failure mode.
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🌍 The bigger picture
This matters because:
• many bacteria in natural worm environments can produce PHB
• PHB production depends on nutrient context
• host survival depends on bacterial metabolism, not just species
So ecology is not static.
It’s state-dependent chemistry interacting with biology.
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🧠 The take-home message
This is not about a toxin.
It’s about material inside bacteria becoming lethal through ingestion.
And more broadly:
what microbes make — and when they make it — can reshape host physiology completely.
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📄 Paper discussed
Giese, G. E.; Richards, D. M.; Florman, J. T.; Starbard, A. N.; Xu, A. A.; Durning, D. J.; Alkema, M. J.; Walhout, A. J. M. (2026)
Bacteria producing the bioplastic polyhydroxybutyrate kill the nematode Caenorhabditis elegans
PLOS Biology
https://doi.org/10.1371/journal.pbio.3003748
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