In process that is shrouded in mystery, rod-shaped bacteria reproduce
by splitting themselves in two. By applying advanced mathematics to
laboratory data, a team led by Johns Hopkins researchers has solved a
small but important part of this reproductive puzzle.
findings apply to highly common rod-shaped bacteria such as E. coli,
found in the human digestive tract. When these single-celled microbes
set out to multiply, a signal from an unknown source causes a
little-understood structure called a Z-ring to tighten like a rubber
band around each bacterium's midsection. The Z-ring pinches the
rod-like body into two microbial sausages that finally split apart. To
shed light on this process, the Johns Hopkins-led team developed a
mathematical tool that computed the mechanical force exerted by the
Z-ring when it helps these cells split.
The calculation will aid scientists who are trying to learn more about
how these microbes live and reproduce. The work also may hasten the
development of a new type of antibiotic that could disable the Z-ring
to keep harmful bacteria in check.
The bacteria research was
reported in the Oct. 9 edition of Proceedings of the National Academy
of Sciences. The work was led by Sean X. Sun, an assistant professor of
mechanical engineering in Johns Hopkins' Whiting School of Engineering.
type of bacteria is commonly found in the human body," said Sun, a
co-author of the journal article. "Understanding how organisms like
this work can help us find new ways to treat bacterial illnesses,
develop medications or do any type of bioengineering involving
bacteria. If you want to target certain cellular activities, you need
to know how single-celled creatures like this operate."
team brought a fresh perspective to the study of cell activity. While
traditional biologists try to identify and learn the function of tiny
of bits of genetic material within cells, Sun studies how such proteins
work together to form "molecular machines" that carry out tasks inside
the cells. "Biologists are just beginning to understand that mechanical
processes at the cellular level are also important," he said. "I'm
bringing the tools of mechanical engineering to bear on biological
Toward this goal, Sun's team's sought to measure how
much mechanical force the Z-ring applies to rod-shaped bacteria during
cell division. The researchers knew that each rod-shaped bacterium
possesses, around the inside of its midsection, a belt made of a
filamentous protein called FtsZ. Most of the time, this ring is
inactive. But when a bacterium cell is healthy and has sufficient food,
it seeks to reproduce by dividing in two. When it is time for this to
occur, the Z-ring receives a signal and begins to contract. This
pinching continues until the rod breaks apart to form two daughter
Sun's team gathered data from microbiology labs that are
studying cell division and then translated these observations into
mathematical equations. The researchers used the equations to create
computer simulations of the cell division process, models that yielded
a prediction of the Z-ring force: 8 piconewtons. A piconewton is
one-trillionth of a newton. One newton is approximately the amount of
force needed to lift a baseball in Earth's gravity.
surprise was that the amount of force generated by the Z-ring was so
small," Sun said. "Most researchers believed a lot more force would be
required during the cell division process."
could be used, Sun said, by drug developers seeking a way to disable
the Z-ring so that harmful bacteria can no longer reproduce. The
research has wider implications as well. "Our mathematical equations
could also be used to help understand how plant and animal cells
divide, including human cells," Sun said. "Human cells have an actin
ring that behaves the same way as a Z-ring. It contracts during
division. The mathematical formulas developed in this study could also
be used in research concerning the division of human cells. The more we
know about this process, the better we can affect the process through
drugs or genetic manipulation."
Source: Johns Hopkins University. October 2007.