DNA defines the spot where bacteria divide
17 April 2012Using the odd-shaped bacteria that they recently discovered, scientists from the Kavli Institute of Nanoscience at Delft University of Technology have discovered that DNA acts as a major scaffold which accurately coordinates the location of proteins that mediate the cell division. The researchers published their results in the scientific journal PNAS.
Cell division is one of the most critical events in all life forms. In this process, cell wall and membrane are built to divide the mother cell into two daughter cells. For bacteria to successfully divide and produce offspring, the cell wall has to be built in the right location in a reliable manner.
Prof. Cees Dekker from the department of bionanoscience, who supervises the work together with Dr. Juan Keymer, says, "Regular E. coli bacteria, which look like small rods, are able to build the new separating wall very accurately in the middle of the cell. Studying E. coli bacteria on lab-on-a chip devices a few years ago, we noticed that these cells were also able to grow surprisingly well in slits that are even narrower than the cell itself. In these slits, they changed their shape drastically to a flat 'pancake-like' phenotype. The bacteria also grew much larger. Remarkably, they were still able to divide correctly and give rise to offspring, despite their irregular shape."
Being surprised by this phenomenon, the research team from Delft started to analyse how the cell division process takes place in this new form of bacterial cells. Again the division was found to be very accurate which was unexpected given the large and irregular shapes. "We asked the question what mechanism allows the two daughter cells to inherit essentially the same volumes, even though their shapes were very so odd."
What underlies this remarkable observation? The researchers studied two systems. In the first, called the Min system, certain proteins diffuse and react with each other and give rise to a pattern that facilitates accurate division via their time-averaged concentration profiles. While the team found this system to work well in regular shapes, they often behave radically different in irregular shapes.
"Then we looked at a different mechanism, proposed by prof. Conrad Woldringh and colleagues from the University of Amsterdam", says Jaan Männik, the postdoc who was leading the work. "According to this mechanism, the DNA chromosomes act as a guide for the placement of cell division proteins. The idea is simple: in areas where DNA is present, no cell-division proteins will adhere to initiate the division, whereas they will assemble in DNA-free regions. Whether and why this is so, still remained a matter of dispute."
By marking the chromosomes and cell-division proteins with different colors - provided through proteins made by co-author prof. David Sherratt and co-workers - the authors found that this indeed explained the observations in the odd-shaped cells.
"The important finding of our work is that compacted DNA in bacterial cells is found to be a key coordinator for positioning the cell wall in these very irregularly shaped bacteria. Thus, besides its well-recognised role as a carrier of genetic information in the cell, the DNA also acts as a structural scaffold in E. coli which coordinates the location of proteins involved in cell division, but possibly also in other functions."