In 2006, Anderson and his colleagues unveiled a bacterium they had
engineered to invade nearby cells. Importantly, the invasion only occurred
under chosen conditions, including
lack of oxygen, which often occurs near
tumors. Rather than directly combining sensing, computation, and actuation into a single DNA or RNA molecule,
Anderson’s genetic modules communicate using smaller molecules, in
much the same way as normal cells.
When the researchers insert new DNA
into the bacteria, they include special
sequences that respond to other chemicals in the cell or the environment.
They “connect” their modules by inducing this sensitivity to the products
of other genes that they insert. In addition, by requiring that two different
molecules attach to adjacent regions
of DNA, they created the cellular equivalent of an AND gate.
a need to Communicate
The chemical sensitivity of genes gives
cells some ability to communicate with
each other. For example, one of the signals that stimulated Anderson’s bacteria to invade was the well-known “
quorum-sensing” response that kicks in for
some bacteria when they are present in
large numbers. Ron Weiss, a professor
of electrical engineering and molecular biology at Princeton University, has
used the quorum-sensing machinery
to build bidirectional communication
between two groups of bacteria. The
collective behavior constitutes a kind
of computation that reflects the interaction between the two strains, each of
which could be tuned to detect separate
conditions. In some cases, Weiss says,
“a cell that specializes in the detection
of one condition can do it much better than a cell that tries to do too many
things at once.”
From a broader perspective, says
computer scientist Tatsuya Suda of
the University of California at Irvine,
“there’s always communication involved” in micromedicine. The sensing of the environment by the tiny
agents is a kind of communication, he
notes, as is the dispensing of drugs. As
researchers design these tiny communications systems, he stresses, they
need to pay careful attention to noise.
In addition to communicating
with their environment, microscopic
agents may communicate with each
other. As an example, Suda cites regenerative medicine, in which the creation of a replacement organ requires
coordinated response by many agents.
But he admits that, for now, “the state
of the art is just trying to find out how
they work together as a group, as opposed to how we can take advantage of
group behavior.”
For biologically based agents, as for
ordinary cells, any communication is
likely to occur through the emission
and sensing of molecules. In contrast,
artificial or hybrid systems incorporating nanometer-scale electronic components might also communicate by
ultrasound or radio. In principle, as
described by researcher Tad Hogg of
Hewlett-Packard Labs, they could signal to point others to medically important locations. In addition, they might
be able to transmit information to the
outside world.
Augmenting, rather than replacing, the diagnostic strengths of the
medical community could be an important early application of micromedicine, and relaxes the demands
for on-board computation and drug
delivery. At a minimum, small devices might extend the capabilities of
chemicals whose locations are monitored in modern medical equipment.
“As those imaging devices advance,”
Hogg says, “they should be able to
give you some information more than
just ‘here’ or ‘not here,’ but what they
found” in a particular region, perhaps
by combining several important local
measurements.
Even before medical applications
become practical, Shapiro suggests,
the emerging tools could provide new
resources for basic biology research.
“I think that these types of molecular computing devices might be able
to analyze living cells ex vivo and help
researchers understand cells without
killing them,” Shapiro notes. “These
applications are probably measured in
years rather than in decades.”
Don Monroe is a science and technology writer based in
murray hill, nJ.
© 2009 acm 0001-0782/09/0600 $10.00
Search Technology
Kleinberg Wins ACM-Infosys Foundation Award
Jon Kleinberg, a professor of
computer science at Cornell
university, is the winner of the
2008 aCm-Infosys Foundation
award in the Computing sciences
for his contributions to improving
Web search techniques that
allow billions of Web users
worldwide to find relevant,
credible information on the ever-
evolving Internet. Kleinberg, 37,
developed models that document
how information is organized on
the Web, how it spreads through
large social networks, and how
these networks are structured
to create the small-world
phenomenon known as “six
degrees of separation.”
Kleinberg’s use of
mathematical models to
illuminate search and social
networking tools that underpin
today’s social structure has created
interest in computing from people
not formerly drawn to this field.
the aCm-Infosys Foundation
award, established in 2007,
recognizes personal contributions
by young scientists and system
developers to a contemporary
innovation that exemplifies the
greatest recent achievements in
the computing field. Financial
support for the $150,000 award is
provided by an endowment from
the Infosys Foundation.
“Professor Kleinberg’s
achievements mark him as a
founder and leader of social
network analysis in computer
science,” says Professor Dame
Wendy hall, president of aCm.
“With his innovative models and
algorithms, he has broadened
the scope of computer science
to extend its influence to the
burgeoning world of the Web
and the social connections it
enables. We are fortunate to
have the benefit of his profound
insights into the link between
computer network structure
and information that has
transformed the way information
is retrieved and shared online.”
the aCm-Infosys
Foundation award recognizes
young researchers who are
currently making sizeable
contributions to their fields
and furthering computer
science innovation. the goal is
to identify scientifically sound
breakthrough research with
potentially broad implications,
and encourage the recipients to
further their research.