Econ_May_26

The Economist

May 26th 2018

Science and technology 73

Recycling plastic

Worm food

LASTICproduction has tripled over

the past 25 years, and themess it

causes has risen commensurately. Recy-

cling is one option. Another is biology,

andwith that inmind researchers have

been hunting for creatures that can digest

plastics. Several species of fungi and

bacteria can do the job, but only slowly.

NowAnja Brandon, a student at Stanford

University, and her research supervisor,

CraigCriddle, have found that bacteria in

the guts ofmealworms can breakdown

polymersmuchmore quickly.

Other researchers had already found

that mealworms can digest a particular

plastic called polystyrene. Ms Brandon

andDr Criddlewonderedwhether poly-

styrenewas uniquely palatable, or

whether the bacteria in theworms’ guts

might be able to eat other sorts of plastic,

too. To check, they turned to polyethyl-

ene, which is bothmore common than

polystyrene and very different in chemi-

cal terms. If theworms found it nutri-

tious aswell, that would suggest their

tastesmight be usefullywide-ranging.

As they describe in

Environmental

Science &Technology

, the researchers

divided theirworms into groups. Some

were given1.8 grams of either polyethyl-

ene or polystyrene. Somewere given

both. Others had their plasticmeals

supplementedwithwheat bran. (Wheat

bran had been found to increase the rate

at whichmealworms could digest poly-

styrene). Acontrol group ofwormswas

fed only bran.

More than 90% of theworms sur-

vived the 32-day experiment. Those fed

only polyethylene found it very agree-

able, polishing off0.87 of their1.8-gram

helping. That was significantlymore than

theworms eating polystyrene, who

managed just 0.57 grams of the stuff. Best

of all were theworms that were given

branwith their plastic. They chewed

through1.1 grams of polyethylene and

0.98 grams of polystyrene.

Norwere the insectsmerely chewing

up the plastics and then passing them in

their faeces. Instead, chemical reactions

in their gutswere converting them into

carbon dioxide. The conversion ratewas

lowat first, but by the end of the experi-

ment theworms fed polyethylenewere

converting 50% of it into gas and those

fed polystyrenewere converting 45%.

Ms Brandon andDr Criddle theorised

that the bacterial ecosystems inside the

insects’ gutswere changing to fit their

unusual diets. They dissected theworms

at the end of the experiment and com-

pared the gut fauna of those that had

been eating plasticswith the fauna found

in the control group. They found big

differences, with several types of bacteria

beingmore common in the guts ofmeal-

worms that had been fed plastic.

The researchers argue that not only

aremealworms probably capable of

digesting awide range of plastics, but

that the protean nature of their gut bacte-

ria should allow them to specialise in a

particular sort relatively quickly. A small

population of a thousandworms, they

reckon, might manage to devour 0.32

grams of polyethylene or 0.28 grams of

polystyrene in a day. That is still not

lightning fast. But it is quicker thanwait-

ing for it to breakdown in a landfill.

Mealworms are the newchampions in the plastic-eating stakes

Dinner is served

genes throughout their lives, switching dif-

ferent genes onandoffas circumstances re-

quire. It is possible that such “epigenetic”

phenomena can be passed, alongwith the

genes themselves, to an animal’s descen-

dants. They offer a mechanism by which

an animal’s life experiences can have ef-

fects on its offspring.

Hunting for signs of this, Dr Feig and his

colleagues asked 28 male volunteers to

complete a questionnaire assessing the se-

verity of any trauma they had experienced

as youngsters. They also asked their volun-

teers to provide sperm samples. They then

looked for evidence for a common epige-

netic mechanism involving small mole-

cules called micro-

RNA

s. Their job is to

bind to another molecule called messen-

ger

RNA

, whose taskin turn is to ferry infor-

mation read from a gene to the cellular fac-

tories that create the required protein.

Micro-

RNA

renders messenger

RNA

inac-

tive, reducing the activity of the gene in

question—and it can travel in sperm along-

side

DNA

Sure enough, upon screening themen’s

sperm, the researchers found that concen-

trations of two types of micro-

RNA

miR-34 and miR-449, were as much as 100

times lower in samples fromabusedmen.

The team then turned to their mice. A

standard way to stress mice is to move

them to new cages, with new mice, from

time to time until they reach adulthood.

When the teamdid this they found that the

stressed males had lower levels of mi

-34

and mi

-449 in their sperm. They mated

these males with unstressed females. The

resulting embryos also had low levels of

the two micro-

RNA

s. And so in turn did

sperm produced by the male offspring of

these unions.

Dr Feig and others have shown that the

female offspring of stressed male mice

tend to be more anxious and less sociable.

Furthermore, the sons of stressed fathers

themselves produce stressed daughters.

The effects of cage-shuffling, in other

words, seem to last for at least three gener-

ations. The researchers have not demon-

strated conclusively that miR-34 and

miR-449 are responsible. But their results

are suggestive.

To try to nail their case, the researchers

plan to carry out a bigger study. This time,

they will give questionnaires to their hu-

man subjects’ fathers, to tease out whether

any epigenetic changes they observe arise

fromthe childhood experiences ofthe sub-

ject or his father. Sisters anddaughtersmay

be included in the study, too. That is an am-

bitious goal. It is also a worthy one. Unless

genetic engineering can one day be per-

fected, changes in genes are hard-wired.

But epigenetic effectsmight be treatable, by

boosting levels ofparticularmicro-

RNA

s in

sperm, for example. That could mean the

legacy of abuse is no longer passed to fu-

ture generations.