there must be some specific part of the bacteria
that fosters the disease,” Jobin said.
Ernesto Pérez-Chanona, a grad student in
Jobin’s lab, searched the literature and found that
only a few bacterial genes in E. coli have been
shown to damage human DNA. When Jobin’s
team analyzed the genes of this specific E. coli
species, they found only one known DNA damager — a string of genes encoded on what’s
called a polyketide synthase island, or PKS.
Jobin says PKS is like a factory. It’s composed
of 22 genes and produces colibactin, which is
toxic to human cells.
With that bit of knowledge, Jobin and Arthur
collaborated with UNC colleague Jonathan
Hansen, who deleted the PKS gene factory in E.
coli so the bacteria couldn’t produce colibactin.
Then the researchers added the strain of E. coli
to mice. When Arthur studied the mice, she
found some precancerous cells in their colons —
“some very early signs of something that looked
off,” she said. “But we didn’t see huge tumors
like we saw in the PKS mice.”
The odd thing is that all the mice — with or
without PKS — had the same amount of inflam-
mation, but the mice with PKS had more DNA
damage, further evidence that the bacteria — not
inflammation — were driving the cancer.
“We have a proof of principle that inflammation may not be sufficient to promote colon cancer,” said Jobin, whose team published its findings in the journal Science. Gut microbes have
the ability to damage DNA and promote cancer.
Yet, genetically altered mice are far from
“In animal models, we control for every-
If these bad bugs could trigger cancer, then
thing,” Jobin said. “In humans, there are other
factors. But if a person has continuous episodes of
stress, poor diet or inflammation — if microbes
gain access to the gut lining because the mucosal
layer is changed, and you have too many of these
E. coli — then the E. coli could be another con-
tributing factor for colon cancer.”
In fact, Jobin’s team found that patients with
colon cancer have a higher prevalence of E. coli
that contain the PKS gene factory than do people
without colon cancer.
Jobin and Arthur wondered whether good bugs
could prevent it.
The probiotics in yogurt and pills don’t natu-
rally occur in your gut in high density. They
don’t colonize, which is why some people take
probiotics daily. Some studies have shown that
probiotics can help alleviate gastrointestinal prob-
lems in people. And probiotics — fibrous foods
such as onions, garlic and leeks — can promote
beneficial bacteria that naturally occur in our
digestive tracts. Several animal studies have
shown that probiotics given to healthy mice pre-
vent inflammation. But Arthur wanted to know
whether probiotics could reverse inflammation
and whether that would prevent cancer.
research magazine at
▼ The story of the last,
great steam railroad in
the U.S., told in photos:
O. WINSTON LINK © CONWAY LINK
▲ An undergraduate
digital photo slideshow
is dedicated to the
Evan Dellon won a
research on a newly
of the esophagus: