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.

⸻

⚡ 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.

⸻

🧠 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. 

⸻

🧠 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.

⸻

🧠 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.

⸻

🌍 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.

⸻

🧠 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.

⸻

📄 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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