18 THE SCIENTIST | the-scientist.com
That led him and his colleagues to
set up the lines of petri dishes at six
spots in the desert: three east of the
town of Tocopilla and three east of the
port city Iquique, 228 kilometers to the
north. The team filled the majority of
the dishes with agar and one of four dif-
ferent growth media, and left the rest
empty to measure the amount of dust
blowing into each region. The agar-
filled dishes were collected an hour after
they were set out, aseptically sealed, and
brought back to the lab, where they were
left untouched for two weeks. Then,
the researchers opened them up and
cultured any bacteria inside, growing
enough to analyze their DNA.Across the six sites, the team iden-
tified 28 microbial species: a mix of
bacteria, bacterial spores, and fungi
usually found in ocean and mountain
sediments, some as far away as China
and India. The greatest numbers of
microbes were found on plates collected
in the afternoons, suggesting that the
tiny organisms were, as Azua-Bustos had
suspected, riding in on airborne dust.
Imagining the desert as a proxy for the
Red Planet, the researchers argued in
a recent paper that any microbial Mar-
tians of the past, or even of the present,
might move around in the same way (Sci
Rep, 9:11024, 2019).
Kai Finster, a microbiologist at Aar-
hus University in Denmark who was not
involved in the work, says it would not
be surprising if microbes in the Atac-
ama travel on dust particles in the wind.
This type of travel, called aeolian trans-
port, “takes place all over the world,” he
says. “It’s not specific to the Atacama
Desert.” Scientists are learning moreabout just how resilient microbes are to
extreme environments, he adds, whether
it’s extreme ultraviolet radiation, arid
environments, or both. When microbes
move in the wind, there’s “a lot of stress
they have to deal with,” he says, but the
reward is great: an entirely new environ-
ment with novel resources and poten-
tially less competition.
It’s not yet clear whether species hitch-
ing a lift into the Atacama Desert from the
ocean or the coast can colonize the soil;
that’s a question the team is now trying to
answer, Azua-Bustos says. The odds might
not be so good, at least at the soil surface,
notes Rafael Navarro-González, an astro-
biologist at the National Autonomous
University of Mexico who wasn’t involved
in Azua-Bustos’s study. The problem is
perchlorate, a naturally occurring chemi-
cal found in the top few millimeters of the
soil at María Elena South—and on Mars—
that is toxic to living creatures. Perchlo-
rate and ultraviolet radiation combined
can be particularly lethal for bacteria, a
strike against finding life at the surface of
the Red Planet.
There might be another problem,
Finster notes: the viability of the wind-
riding bacteria themselves. In lab experi-
ments, he and his colleagues took spores
of Bacillus subtilis, a species often
found in soil, mixed them with min-
erals, and then shook them gently for
days to simulate traveling in the wind.
“We thought that [the bacteria] would
survive for some weeks or so,” he says,
but the researchers weren’t able to cul-
ture any of the bacteria after the experi-
ment. They decided to cut the shaking
time to a minute, and still, he says, the
cells were killed. An examination of the
shaken spores using an electron micro-
scope revealed that they’d fallen apart
(Astrobiology, 19:497–505, 2019).
Azua-Bustos, however, is undeterred,
continuing his tests to see whether the
species in the Atacama can endure the
physical and chemical stresses. He’s
even begun testing whether some spe-
cies in the desert might not only be tol-
erant to ultraviolet radiation but use it
as a source of energy. In parts of the Ata-cama, rocky surfaces are covered with a
black biofilm, where microbial species
appear to be absorbing all visible—and
perhaps some invisible—wavelengths
of the electro magnetic spectrum. It’d
be exciting to find evidence that these
microbes exploit ultraviolet rays or
other types of light that can’t be seen
by humans, Azua-Bustos says. But even
just detecting microbes in the Atacama
is “a fantastic sign that you can find life
almost anywhere.”
—Ashley YeagerHot Cell
It was a simple question—deceptively
simple, as it turned out: Can naturally
occurring temperature fluctuations in
neurons alter the cells’ synaptic transmis-
sions? Some experiments suggest these
signals might be heat-responsive. The
speed at which mouse neurons release
calcium, for example, is lower in tissue
sections kept at 25 °C than in those at
physiological temperature.
A few years ago, neurosurgeon Huan
“John” Wang, then at Carle Hospital
in Urbana, Illinois, approached San-
jiv Sinha, a mechanical engineer at the
nearby flagship campus of the Univer-
sity of Illinois, about working together
to answer that question. To do so, Sinha’s
team would first need to figure out how
to take a cell’s temperature. Some tech-
niques for this already existed, but the
researchers thought there was room for
improvement. For example, one popu-
lar technique involving fluorescent mol-
ecules had a high margin of error and
could be influenced by changes in fac-
tors other than temperature, such as ion
concentrations and pH.
Temperature measurement via fluo-
rescence had also yielded results Sinha
considered questionable. “In the last
ten years or so, there have been numer-
ous publications that report tempera-
ture rises in cells that are a few degrees
centigrade,” he says. “This doesn’t make
physical sense. Where would all this
heat be coming from?”Knowing Atacama is a very
windy place, we wanted to
know whether wind could
transport microbial life.
—Armando Azua-Bus tos,
Center of Astrobiol ogy in Madrid