New Scientist - USA (2021-11-06)

20 | New Scientist | 6 November 2021

News

BACTERIA have been genetically

engineered to enter and live inside

mouse immune cells, where they

released proteins that altered the

behaviour of those cells. The work

is a small step towards creating

“artificial endosymbionts” that

could live inside some human

body cells and do everything

from helping regenerate damaged

tissues to treating cancer.

“That’s the vision in the long

run,” says Christopher Contag

at Michigan State University.

Several other groups are

also developing artificial

endosymbionts, which they say

could allow us to make crops and

farm animals more productive,

or treat age-related conditions.

The idea of creating artificial

endosymbionts used to be

regarded as fanciful, says Bogumil

Karas at the University of Western

Ontario in Canada, but due to

advances in our ability to engineer

organisms in recent years, it is

starting to be seen as feasible.

“This is going to be one of the

biggest things in the very near

future,” he says.

Some bacteria have naturally

evolved to live inside the cells

of plants or animals in a mutually

beneficial relationship called

endosymbiosis.

Endosymbionts can give

organisms abilities vital for their

survival. The energy-producing

structures in all animal and plant

cells evolved from endosymbiotic

bacteria, for example.

To create a new endosymbiont

from scratch, Contag’s team

started with a bacterium called

Bacillus subtilis, found in our guts

among other places.

The researchers engineered it to

produce mammalian proteins that

alter the activity of genes and thus

control what mammalian cells do.

To get the bacteria inside mouse

cells, Contag’s team relied on

the fact that some animal cells

can engulf bacteria via a process

called phagocytosis. Normally,

engulfed bacteria remain trapped

in membrane-bound sacs

where they are digested. But

the engineered B. subtilis strain

secretes a protein that enables

it to break out of these sacs.

The researchers added the

engineered bacteria to mouse

immune cells known as

macrophages growing in a dish.

They managed to get the bacteria

into 99 per cent of cells. They also

showed that the mammalian

proteins the bacteria had been

engineered to produce altered the

behaviour of the macrophages

(bioRxiv, doi.org/g359).

Right now, the bacteria divide

quickly and kill the macrophages

after a few days, so there is more to

be done to make the system work,

say the researchers.

Even so, it is amazing the team

managed to get the bacteria into

such a high proportion of cells,

says Karas. However, achieving

this in the body will be much

more difficult, he says.

John Rasko at the University of

Sydney cautions that even if it is

possible, there will be significant

regulatory hurdles to navigate

before the technology could ever

be used in people. ❚

Genetic engineering

Michael Le Page

Genetically engineered bacteria could

one day heal us from inside our cells

Space exploration

THE first interstellar travellers from

Earth may be a species that is no

stranger to space exploration:

tardigrades. These creatures grow

only 0.5 millimetres long but are

some of the most resilient animals

known to science, even surviving

in the vacuum of space.

Until now, only five craft have

travelled the 18 billion kilometres

to interstellar space, each taking

decades, but a NASA-funded

research project is developing craft

propelled by solar sails, boosted by

Earth-based lasers, that could cover

the distance in days. This opens the

door to sending live organisms.

Stephen Lantin at the University

of Florida and his colleagues

analysed how much food would be

needed to keep various species

alive, how much they weigh and

their resilience to the high levels

of radiation and acceleration they

would encounter on the journey.

Tardigrades come out as a good

option for low-maintenance,

pioneering interstellar travellers

(Acta Astronautica, doi.org/g353).

“It would be nice to send humans,

but there are some biological

constraints that would make it more

favourable for us to send other

organisms, at least in the first few

flights,” says Lantin. “It takes a lot

of energy to send anything out into

interstellar space, at least at the

speeds that we’re proposing.” To

do that, you need a small payload,

he says, and, unfortunately, it would

be a one-way mission.

Tardigrades and the roundworm

Caenorhabditis elegans, another

species in contention, both have

the benefit of being capable of

cryptobiosis, a form of extreme

hibernation in which the animals

radically slow their metabolism

when in adverse conditions such

as desiccation or freezing.

Tardigrades are thought to use

just 0.01 per cent of their normal

energy when in cryptobiosis. They

have already been shown to survive

space flight and exposure to the

vacuum of space on prior missions,

and may have made it to the moon

as part of a failed Israeli mission. ❚

Tardigrades could

survive interstellar

space travel

Matthew Sparkes

“It is amazing the team

managed to get the

bacteria into such a high

proportion of the cells”

Tardigrades go into a form

of low-energy hibernation to

survive tough environments

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