Phenomenology of Bacteriophage T7 Growth on Early Stationary-Phase E. coli Cultures

Bacteriophages play a significant role in the natural regulation of bacterial populations. To date, a substantial body of information has been obtained regarding the mechanisms that enhance bacterial survival upon encounter with bacteriophages. However, most available data concern the interactions between phages and actively growing bacterial cells modeled by exponential growth phase cultures. The interactions between bacteriophages and host cells in the stationary phase of growth remain poorly understood. In this work, we investigated the interactions of phages T7, capable of propagating in early stationary-phase Escherichia coli cultures. We demonstrate that visible expansion of T7 plaques during prolonged (several days) incubation occurs due to efficient phage infection of the mature microcolonies and killing the cells. In contrast to many other phages (e.g., phage T4), the bacteriophage T7 is able to form plaques even if it is applied onto a mature bacterial lawn that already reached the maximal density. The phage readily penetrates into the microcolonies of the lawn to infect the cells through the whole colony volume without getting sequestered at the surface.