Level 1 - Absolute Beginner

Scientists in Germany find a new enzyme. An enzyme is a tiny tool inside a living thing that cuts things up.

This enzyme comes from bacteria in forest soil. It cuts up bioplastic. It does not eat all plastic.

People call it the Pac-Man enzyme. Its mouth is very wide, so big bits of plastic fit inside.

The enzyme also cuts penicillin, a medicine. That is a problem. This is lab work, not a clean-up plan.

enzyme

a tiny tool inside a living thing that cuts things up

bacteria

very small living things that you cannot see with your eyes

soil

the brown earth that plants grow in

forest

a big place with many trees

bioplastic

a kind of plastic that can break down in nature

wide

big from one side to the other side

medicine

something you take to get better when you are sick

lab

a room where scientists work and test things

Level 2 - Elementary

Researchers at the University of Konstanz in Germany have found a new kind of enzyme in bacteria. Enzymes are tiny tools inside living cells, and this one cuts up plastic. The team published the work in a science magazine for researchers called The ISME Journal.

The scientists did not find the enzyme in a clean laboratory dish. They took soil from a forest where bioplastic had been buried, and they studied the mix of tiny living things in it. Inside that community they found the gene for the enzyme.

The enzyme is a type of esterase, but people now call it the Pac-Man enzyme. The reason is its shape. The active site, the part that does the cutting, is unusually wide and open, so long plastic chains can slide in and be cut apart. The enzyme also sits on the outside of the bacterial cell, so the small pieces appear right next to the cell and go in quickly.

The enzyme breaks down only some plastics, not all of them. In the soil tests two bioplastics, PHBV and PCL, broke down completely. But there is a worry too. The enzyme can also cut penicillin, which is an antibiotic, so it may help bacteria survive that medicine. For now this is laboratory and soil research, not a way to clean up plastic waste.

enzyme

a tiny tool inside a living cell that cuts or changes other things

esterase

a type of enzyme that cuts a chemical link called an ester bond

active site

the part of an enzyme where the cutting work happens

bioplastic

plastic that tiny living things can break down in nature

gene

a piece of instructions inside a living thing that tells it how to make something

bacterial cell

the single small body that one bacterium is made of

antibiotic

a medicine that kills bacteria or stops them growing

penicillin

one of the oldest and best known antibiotics

Level 3 - Intermediate

A discovery announced by the University of Konstanz has given plastic researchers something to hope for and antibiotic researchers something to worry about. Harry Lerner, then a postdoctoral researcher, working with the senior scientist David Schleheck, a professor of microbial ecology and limnic microbiology, led a team that described a previously unknown type of plastic degrading enzyme carried by soil bacteria. The paper appeared in The ISME Journal.

The enzyme is an esterase, and it has been nicknamed the Pac-Man enzyme because its active site, the pocket where the chemistry happens, is unusually wide and open. Most enzymes accept only small, neatly shaped molecules, whereas this one allows long polymer chains to enter and be cut apart. It is anchored to the outer surface of the bacterial cell, which means that plastic is chopped into fragments immediately next to the cell, where the pieces can be absorbed quickly. The gene itself was not taken from a single named species but from a microbial community sampled in forest soil where bioplastic had been buried.

The helpful side of the finding is real but limited. The enzyme attacks polyesters and bioplastics, specifically the long chain aliphatic polyesters known as LCAP, and in the soil experiments the bioplastics PHBV and PCL degraded completely. This is not a cure for ordinary plastic drink bottles or for plastic waste in general, and nothing is being used in the field today. What it does suggest, in Schleheck's encouraging reading, is that microbes may be adapting to the plastics we make faster than anyone expected.

The worrying side comes from the enzyme's family resemblance. Its structure looks like that of the beta lactamases, the enzymes bacteria use to break the beta lactam ring in drugs such as penicillin, and the Konstanz team confirmed in the laboratory that the new enzyme cleaves penicillin as well. Because it works outside the cell, it can inactivate an antibiotic before the drug ever gets in. That matters for the plastisphere, the community of microbes that lives on plastic debris and is already known to carry many antibiotic resistance genes.

esterase

an enzyme that cuts ester bonds, the chemical links found in polyesters

active site

the pocket in an enzyme where the chemical reaction takes place

polymer chain

a long molecule made of many small units joined in a row

long chain aliphatic polyester

a polyester built from long, straight carbon chains, abbreviated LCAP

beta lactamase

a bacterial enzyme that breaks the beta lactam ring in antibiotics such as penicillin

plastisphere

the community of microbes that lives on pieces of plastic in the environment

antibiotic resistance

the ability of bacteria to survive a drug that is meant to kill them

Level 4 - Advanced

Few scientific findings arrive with their moral ambiguity already built in, but the enzyme described by a team at the University of Konstanz manages it. Writing in The ISME Journal, Harry Lerner, then a postdoctoral researcher in the laboratory of David Schleheck, professor of microbial ecology and limnic microbiology, reported a previously unrecognized class of plastic degrading esterase, retrieved not from a single cultured species but from the mixed microbial community of forest soil in which bioplastic had been buried.

The nickname, the Pac-Man enzyme, is a comment on architecture rather than on appetite. Enzymes are usually fussy about their substrate, since the catalytic pocket is shaped to admit one sort of molecule and exclude the rest. This one presents an unusually wide, open active site, roomy enough for long polymer chains to enter and be severed. It is also anchored to the exterior of the bacterial cell, so the polymer is dismantled at the cell surface and the fragments are absorbed almost as soon as they are released.

The constructive reading is narrower than a headline suggests. The enzyme acts on polyesters and bioplastics, specifically the long chain aliphatic polyesters known as LCAP, with the test materials supplied by the group of Stefan Mecking; in soil incubations PHBV and PCL degraded completely. Nothing here is in service today, and ordinary plastic waste is untouched. Its value lies with biodegradable polymers whose ester bonds microbes can break apart, the plastic that escapes recycling, and in Schleheck's hint that soil communities may be adapting to our polymers faster than expected.

The unsettling half of the result is a matter of family resemblance. Structurally the enzyme recalls the beta lactamases, the bacterial enzymes that open the beta lactam ring at the heart of penicillin, and the Konstanz group confirmed in vitro that it cleaves penicillin too. Because it works outside the cell, it can inactivate the drug before the drug reaches its target. Set that beside the plastisphere, the microbial film that colonizes plastic debris and is already rich in resistance genes, and the tool that might help clear our waste also looks like a route by which our medicines are blunted.

esterase

a hydrolytic enzyme that cleaves ester bonds, the linkages that hold polyester chains together

substrate

the molecule on which an enzyme acts

catalytic pocket

the shaped cavity in an enzyme that binds the substrate and carries out the reaction

long chain aliphatic polyester

a polyester built from long, unbranched carbon chains, abbreviated LCAP

beta lactamase

a bacterial enzyme that hydrolyzes the beta lactam ring, disabling penicillin and related drugs

beta lactam ring

the four atom ring at the chemical heart of penicillin and its relatives