Abstract
We present evidence that mucoidy provides a general answer to the longstanding question of how lytic phage are maintained in bacterial populations. In serial transfer culture, populations of mucoid E. coli MG1655 that appear to be broadly resistant to lytic phage with different receptors are capable of maintaining these phage with little effect on the total density of bacteria. Based on the results of our analysis of a mathematical model, we postulate that the maintenance of phage in populations dominated by mucoid cells can be attributed to high rates of transition from the effectively resistant mucoid states to susceptible non-mucoid states. Our test of this “leaky resistance” hypothesis with both population dynamic and single cell experiments are consistent with it. We discuss reasons for the generalized resistance of these mucoid E. coli, and the genetic and molecular mechanisms responsible for the high rate of transition from mucoid to sensitive states.