IMAGE: NASA’S GODDARD SPACE FLIGHT CENTER CONCEPTUAL IMAGE LAB368 28 JANUARY 2022 • VOL 375 ISSUE 6579 science.org SCIENCENEWS | IN DEPTH
F
or tens of thousands of people fight-
ing repeat infections of the diarrhea-
causing bacterium Clostridium dif-
ficile each year, there’s a proven, if
unappetizing treatment option: a
transplant into their intestines of
stool from a healthy donor. The transplant,
often delivered via colonoscopy, can restore
a balanced community of gut microbes and
clear the potentially deadly infection.
But several companies are eager to
achieve the same effect with more de-
fined collections of microbes that can be
protected with patents and marketed as a
drug in the United States. One option, a pill
containing bacterial spores isolated from
human feces, has now passed the critical
test of a phase 3 clinical trial, paving the
way for its approval in the United States
and elsewhere.
“It’s a step forward for the field, for
sure,” says Colleen Kelly, a gastroentero-
logist at Brown University who was an
investigator on an earlier trial of the pill,
called SER-109. She and others note that
reliable sources of acceptable stool for
transplants are dwindling in the United
States, increasing the need for alternatives
like SER-109. “[For] the majority of patients
that we see for recurrent C. diff ... it might
be able to solve the problem,” she says.
C. difficile is most common in elderly
patients with other health problems, and
often starts when antibiotics deplete the
normal gut microbiome. A fecal micro-
biota transplant (FMT) can break the cycle
of recurrent infections. But the contents
of the fecal material for these procedures
vary—as do safety screening processes,
says Sahil Khanna, a gastroenterologist
at the Mayo Clinic who was also involvedAlternatives
to fecal
transplants
near approval
Trial shows spore-filled
pill derived from
human stool treats tough
gut infections
BIOMEDICINEBy Kelly Servickexpecting to see 18 separate dots, one from
each segment. “It will be very misaligned,”
says Lee Feinberg, Webb telescope manager
at Goddard.
Each segment will be wiggled to see which
dot it is producing. Then begins the process
of adjusting the tilt of each segment until the
dots are all stacked on top of each other in
the sensor’s view. At the same time, operators
will adjust the curvature of the segments to
make each spot as small and sharp as pos-
sible. “It’s a painstakingly detailed sequence
of steps,” Feinberg says.
The last step is “phasing,” ensuring that
the light is not only focused, but also in tune,
with the peaks and troughs of the waves
from all 18 segments coinciding. To ensure
the light paths are all the same length, op-
erators will adjust the segments’ distance
from the secondary mirror by fractions of a
wavelength of light—ten-thousandths of the
width of a human hair. Only then will the
18 separate segments have the resolution
of “a beautiful monolithic primary mirror,”
Feinberg says, and “a star will look like a
star.” It will be the start of a lifelong process:
Operators will continue to check Webb’s op-
tics every 2 days and will tweak the segment
positions, as required, every 2 weeks. “If
they drift by one-twentieth of a wavelength,
we care about it,” Feinberg says.
After tuning the mirror with the help of
NIRCam, operators will check that light
passes cleanly into two other detectors, the
Near Infrared Spectrograph and the Near
Infrared Slitless Spectrograph. A fourth sen-
sor, the Mid-Infrared Instrument (MIRI),
operates at much lower temperatures than
the other three, just 6.4° above absolute zero.
It requires a mechanical cryocooler which,
because it emits waste heat, must sit on the
warm side of the sunshield and pipe its cool-
ant through to MIRI—one of Webb’s most
challenging systems to build. Once MIRI is
fully cooled in early April, it, too, will be opti-
cally aligned.
By early May, operators expect to be testing
all 17 observing modes of the instruments.
Commissioning involves viewing a range of
reference objects, such as stars with precisely
known brightness or star fields with exactly
measured positions. Researchers want to
understand how a sensor’s output relates to
the influx of light and whether the telescope’s
internal optics distort the positions of stars.
Operators will also point the telescope at
starless areas of sky to understand the “dark
current” created by thermal noise in the in-
strument itself. “We don’t want the finger-
prints of the instrument on the science,” says
Scott Friedman, Webb commissioning scien-
tist at the Space Telescope Science Institute.
He and his colleagues want to be sure
the telescope can stay on target, too. “Posi-tioning has to be exquisite,” Friedman says.
They will test Webb’s Fine Guidance Sen-
sor, which enables a laserlike lock on mov-
ing targets such as the moons of Jupiter, or
anything that requires long exposures, such
as dim exoplanets or distant galaxies. In the
final weeks, operators will test the observato-
ry’s thermal stability when pointed in differ-
ent directions. Although the sunshield keeps
the mirror and instruments in permanent
shadow, sunlight heats the spacecraft differ-
ently at its pointing extremes, and one-tenth
of 1°C can have an effect. “Those sort of tem-
perature changes matter,” Feinberg says.
At the end of all that, 6 months after its
Christmas Day launch, science observa-
tions can begin, and astronomers will see
what Webb is capable of. Friedman says:
“This is what we’ve worked for, for years
and years.” jThe James Webb Space
Telescope’s 18 mirror
segments must be
focused and tuned to work
in concert as a single,
6.5-meter-wide mirror.