Figure 1.

More than One Copy of Phage DNA Is Required for Lysogenic Establishment

(A) Representative images showing lytic and lysogenic events by λWT. Top: a cell is apparently infected by one λWT phage (blue dot at 0 min), and subsequently gpD-mTurquoise2 expression (blue) is observed. Cell lysis is observed at 195 min. Bottom: a cell is apparently infected by one λWT phage (blue dot at 0 min). cI reporter expression (yellow) and cell division are observed, indicating a successful lysogenization event.

(B) Representative images of lysogenic and failed infection by λP^-. Top: a cell is apparently infected by 3 λP^- phages (blue dots at 0 min). The cell divides, and expression of the cI reporter (yellow) is observed, indicating lysogenization. Bottom: a cell is apparently infected by one λP^- phage (blue dot at 0 min). The cell does not divide, and only minimal expression of gpD-mTurquoise2 is detected, indicating that the phage failed to reach either the lytic or lysogenic decision.

(C) Lysogenization frequency of λWT and λP^-. For both phages, the lysogenization frequency increases with MOI. λP^- has lower lysogenization frequencies at MOI ≤ 3, and reaches a similar level at MOI = 4. At MOI = 1, no lysogenization events (0 of 35 infections) are observed for λP^-. Error bars denote SEM.

Scale bars denote 2 μm. See also Figures S1 and S2.