Scientists at The
Scripps Research Institute have unraveled a complex chemical pathway that
enables bacteria to form clusters called biofilms.
Such improved understanding might eventually aid the development of new
treatments targeting biofilms, which are involved in a
wide variety of human infections and help bacteria resist
antibiotics.
Biofilm formation is a
critical phenomenon that occurs when bacterial cells adhere to each other and to
surfaces, at times as part of their growth stage and at other times to gird
against attack. In such aggregations, cells on the outside of a biofilm might still be susceptible to natural or
pharmaceutical antibiotics, but the interior cells are relatively protected.
This can make them difficult to kill using conventional treatments.
Past
research had also revealed that nitric oxide is involved in influencing
bacterial biofilm formation. Nitric oxide in
sufficient quantity is toxic to bacteria, so it's logical that nitric oxide
would trigger bacteria to enter the safety huddle of a biofilm. But nobody knew precisely how. In the new study,
the scientists set out to find what happens after the
nitric oxide trigger is pulled. "The whole project was really a detective story
in a way," said Plate.
To
learn more, the researchers used a technique called phosphotransfer profiling. This involved activating the
histidine kinase and then
allowing them to react separately with about 20 potential targets. Those targets
that the histidine kinase
rapidly transferred phosphates to had to be part of the signaling pathway.
"It's
a neat method that we used to get an answer that was in fact very surprising,"
said Plate.
The
experiments revealed that the histidine kinase phosphorylated three proteins
called response regulators that work together to control biofilm formation for
the project's primary study species, the bacterium Shewanella oneidensis, which
is found in lake sediments.
Further
work showed that each regulator plays a complementary role, making for an
unusually complex system. One regulator activates gene expression, another
controls the activity of an enzyme producing cyclic diguanosine monophosphate, an
important bacterial messenger molecule that is critical in biofilm formation, and the third tunes the degree of
activity of the second.
Since
other bacterial species use the same chemical pathway uncovered in this study,
the findings pave the way to further explore the
potential for pharmaceutical application. As one example, researchers might be
able to block biofilm formation with chemicals that
interrupt the activity of one of the components of this nitric oxide
cascade.
