by Suckjoon Jun
I entered the bacterial chromosome field in 2004 as a fresh Ph.D. trained in theoretical physics. Ten years is not long enough for one to gain the depth and breadth of a scientific discipline of long history, certainly not for an early career scientist to write an essay of the status of A Mathematician’s Apology (Hardy 1940). Nevertheless, I agreed to write this Perspective as a physicist who entered biology, because my colleagues are often curious to know what drives physicists to become (physical) biologists, and make them stay in biology despite many challenges. I also wanted to share several lessons I have learned because, while some of them are personal and specific to my field, I have a good reason to believe that they might resonate with many future travelers. This Perspective is for them.
I would like to start with the story of one of the most familiar and yet mysterious forces in nature—gravity. Galileo is said to have dropped two balls of different masses from leaning Tower of Pisa in Italy some five hundred years ago. His experiment was to demonstrate that, on the contrary to Aristotle’s theory, the falling rate of the balls was independent of their mass. A modern version of this experiment was performed on the Moon by the Commander of Apollo 15 with a hammer and a feather. For a movie of this experience, click here. When released from the same height at the same time, the two falling bodies hit the surface of the Moon simultaneously! On the Earth, however, the feather would have fluttered, as if alive, because of the air.
Initially attracted to the beauty of Amsterdam, I started my post-doctoral research at AMOLF, an interdisciplinary research institute known for exciting interactions at the interface between physical and biological sciences. The forces I was interested in were much less tangible than gravity. In particular, I was supposed to explain the driving force underlying segregation of a replicating chromosome in Escherichia coli. It sounded simple to me, except that I barely knew anything about bacteria, certainly without realizing that it was one of the long-standing problems in biology. I knew the DNA biophysics literature fairly well, but when I saw the beautiful 1992 illustration of E. coli in Goodsell, it was obvious that something like the wormlike chain model was not going to be very useful to understand segregation of the whole chromosome. What worried me was the directionality—if I were a small protein sitting on a replicating chromosome, could I tell which DNA segment belongs to which sister DNA? Physicists like questions like that, whether they are rooted in physics or biology.