DNA as a Phosphate Reservoir: Spatiotemporal Modeling of Extracellular DNA (eDNA) Dynamics in Biofilms

DNA is the genetic code found inside all living cells and its molecular stability can also be utilized outside the cell. While extracellular DNA (eDNA) has been identified as a structural polymer in bacterial biofilms, whether it persists stably or can be reclaimed for further cellular activity remains unknown. Here, by imaging eDNA dynamics within undomesticated Bacillus subtilis biofilms, we propose to test the hypothesis that DNA acts as a temporary structural scaffold that is later metabolized for cell growth. Specifically, we found that eDNA is produced throughout biofilm development before being degraded in a spatiotemporally coordinated pulse. We identified YhcR, a secreted Ca2+-dependent nuclease, as responsible for DNA degradation. As predicted by a preliminary mathematical model, biofilms lacking this nuclease fail to reclaim DNA for its phosphate contents, thereby decreasing biofilm fitness. Our results identify a secreted nuclease that is crucial for reclaiming eDNA during biofilm development, expanding our knowledge of DNA and suggesting new targets for biofilm control.