Nature Invented Bioplastic Before Humans Did — and Animals Have Been Eating It for Millions of Years

 

No, earthworms haven't secretly been snacking on shopping bags. The real story is much stranger.

Wait... What?

Apparently humans did not invent plastic first.

Nature beat us to it.

By a lot.

Many bacteria and archaea naturally manufacture substances called polyhydroxyalkanoates, or PHAs.

They're polymers.

They're plastic-like.

They're biodegradable.

And microorganisms have been making them as little internal energy reserves since long before humans came anywhere near a petrochemical plant.

Already weird.

But scientists have now discovered something even stranger:

Animals can eat this stuff.

Not just one bizarre animal, either.

Researchers found the biological machinery for breaking down microbial PHAs in animals ranging from marine worms to sponges, starfish, springtails and earthworms.

Which means nature apparently invented plastic...

and then invented animals capable of digesting it.

So, What's the Deal?

First, an important clarification before anybody releases a herd of earthworms into the local landfill.

We are NOT talking about ordinary petroleum-based plastic.

Your grocery bag isn't suddenly worm food.

Neither is your soda bottle.

The material involved here is PHA, a family of naturally occurring biodegradable polyesters manufactured by microorganisms. Bacteria can accumulate PHAs inside their cells when they have excess carbon, essentially using the material as a stored reserve of carbon and energy.

Think of it as bacterial emergency food storage.

We store cans in the pantry.

Squirrels bury nuts.

Some bacteria apparently manufacture microscopic plastic granules.

Everybody has a system.

Scientists already knew microorganisms could produce and break down PHAs.

What researchers didn't realize was how many animals could apparently break them down too.

That discovery started with one particularly strange little worm.

Wait, It Gets Weirder

Meet Olavius algarvensis.

It's a tiny marine worm only about two centimeters long that lives buried in Mediterranean seafloor sediment.

And this animal has made a few unusual lifestyle choices.

It has:

No mouth.

No gut.

And no conventional digestive or excretory system.

Which raises the fairly reasonable question:

How is this thing still alive?

Bacteria.

The worm lives in partnership with symbiotic bacteria beneath its skin. Those microbes provide nutrition, and the worm digests some of them for food.

One of its dominant bacterial partners also stores enormous quantities of PHA.

In fact, researchers found that PHAs could account for up to 42% of the carbon stored in that symbiotic bacterium.

That's a pretty substantial potential food source.

So researchers wondered:

Can the worm actually digest the bacteria's plastic-like energy reserves too?

Turns out...

yes.

Seriously?

Seriously: researchers found an enzyme produced by the worm that can break microbial bioplastic into smaller molecules that can enter ordinary metabolic pathways.

The enzyme belongs to a class called PHA depolymerases, or PHADs.

Researchers experimentally produced the worm's enzyme and demonstrated that it could break down storage PHAs into smaller hydroxyalkanoate molecules.

They also found that the enzyme was being expressed right where the worm digests its bacterial partners.

In other words, this wasn't simply a gene sitting around doing nothing obvious.

The biological pieces lined up with the idea that the animal can access the energy stored inside its bacterial partners' PHA reserves.

That's already an interesting discovery.

Then the researchers started looking elsewhere.

And that's when things got much bigger.

The Rabbit Hole

The team searched genomes from across the animal kingdom.

They found related PHA-degrading enzymes in more than 66 animal species spanning nine different major animal groups, as well as in 19 protist species.

These weren't all closely related creatures living in the same environment.

The researchers found evidence across widely separated branches of animal life and experimentally confirmed PHA-degrading activity in enzymes from animals including a sponge, an earthworm and a springtail.

Ocean.

Land.

Completely different kinds of animals.

Same basic surprise.

And the evolutionary analysis goes even further.

The researchers say the distribution of these enzymes suggests that the common ancestor of animals may already have possessed this capability.

That's where the truly mind-bending implication comes from.

Researchers believe animals may have been exploiting these natural microbial bioplastics as food for hundreds of millions of years.

Humanity's relationship with plastic:

"We invented this relatively recently and now can't figure out how to get rid of it."

Nature's relationship with certain bioplastics:

"We've had a recycling program running since before dinosaurs were fashionable."

Wait — Bacteria Really Make Plastic?

Yep.

PHAs aren't just something scientists decided to call plastic because it makes a good headline.

They're natural polyesters whose physical properties allow them to be processed into useful plastic-like materials.

Humans have actually learned to manufacture PHA plastics by putting bacteria into fermentation tanks and feeding them carbon-rich materials such as sugars, starches or plant oils.

The bacteria accumulate PHA.

We extract it.

Then we turn it into things.

PHA materials are already used or investigated for applications including food packaging, agricultural products, wound dressings, drug-delivery systems and medical materials designed to gradually break down inside the body.

So we've effectively looked at something microbes were already manufacturing naturally and said:

"That's useful. Can we have some?"

Classic humanity.

Does This Mean We've Solved Plastic Pollution?

Absolutely not.

And this is where the distinction really matters.

PHA is not the same material as polyethylene shopping bags, PET drink bottles, polystyrene foam or the many other conventional plastics accumulating in the environment.

Finding animals capable of degrading naturally occurring PHA does not mean scientists have discovered that worms can suddenly clean up ordinary plastic pollution.

What the research does show is that PHAs participate in a biological cycle far more complex than scientists previously understood.

Microorganisms manufacture them.

Microorganisms can break them down.

And now we know that a surprisingly broad range of animals appear capable of breaking them down too.

That may matter as researchers look for materials that can perform useful jobs without persisting in nature the way many conventional plastics do.

But the scientists also stress that they still don't know exactly how important animal PHA digestion is in real ecosystems or how much it contributes to the global carbon cycle.

There's plenty left to figure out.

Okay, But Why Should I Care?

Because we have a habit of thinking technology begins when humans discover it.

It doesn't.

Velcro famously took inspiration from burrs.

Aircraft wings borrow lessons from birds.

Engineers study gecko feet, spider silk, shark skin and countless other biological tricks.

And now here's another reminder:

Nature was manufacturing biodegradable polymers long before we decided plastic was a clever idea.

Better yet, ecosystems apparently developed organisms capable of using some of those polymers as food.

That doesn't magically solve our plastic problem.

But it does remind us that biology has been conducting research and development for a few billion years longer than we have.

Sometimes the smartest thing we can do...

is figure out what it already invented.

Wait, Seriously? Verdict

Long before humans manufactured plastic, microorganisms were already producing natural biodegradable polymers called PHAs to store carbon and energy.

Scientists have now discovered that animals across surprisingly distant branches of the animal kingdom possess enzymes capable of breaking those microbial bioplastics down.

The researchers believe animals may have been feeding on this hidden microbial energy source for hundreds of millions of years.

So no...

Your earthworms aren't going to eat your plastic garbage.

But somewhere beneath your feet and under the ocean, animals may be participating in a natural plastic-making-and-eating cycle that existed unimaginably long before we showed up.

And we only just noticed.

Nature's been doing bioplastics longer than we've been doing... pretty much anything.

Your Turn

What's stranger to you — that bacteria naturally manufacture plastic-like material, or that animals evolved the ability to eat it?

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