Chemotaxis is the process where cells move in response to external chemical gradients. It has mainly been viewed as a foraging and defense mechanism, enabling bacteria to move towards nutrients or away from toxins. We recently found that the Gram-positive bacterium Bacillus subtilis performs chemotaxis towards DNA. While DNA can serve as a nutrient for B. subtilis, our results suggest that the response is not to DNA itself but rather to the information encoded within the DNA. In particular, we found that B. subtilis prefers DNA from more closely related species. These results suggest that B. subtilis seeks out specific DNA sequences that are more abundant in its own and related chromosomes. In this talk, I will discuss the mechanism of DNA sensing and chemotaxis in B. subtilis. I will conclude by discussing the physiological significance of DNA chemotaxis with regards to natural competence and kin identification.

The ability to read the DNA sequences of different organisms has transformed biology in much the same way that the telescope transformed astronomy. And yet, much of the sequence found in these genomes is as enigmatic as the Rosetta Stone was to early Egyptologists. With the aim of making steps to crack the genomic Rosetta Stone, I will describe unexpected ways of using the physics of information transfer first developed at Bell Labs for thinking about telephone communications to try to decipher the meaning of the regulatory features of genomes. Specifically, I will show how we have been able to explore genes for which we know nothing about how they are regulated by using a combination of mutagenesis, deep sequencing and the physics of information, with the result that we now have falsifiable hypotheses about how those genes work. With those results in hand, I will show how simple tools from statistical physics can be used to predict the level of expression of different genes, followed by a description of precision measurements used to test those predictions. Bringing the two threads of the talk together, I will think about next steps in reading and writing genomes at will.