Addition of the energy click here poison KCN halts further holin production and abolishes the pmf. This figure is adapted from Wang et al. [28] and White et al. [40]. Typically, the lysis time of a phage is estimated

using a one-step growth curve [41–43]. In the case of phage λ, however, the availability of thermally-inducible E. coli λ lysogens allows a more precise determination of the lysis time by following the decline of culture turbidity [26, 44]. Direct observation of the lysis of individual λ lysogenic cells [45] confirmed that the precipitous decline of culture turbidity, commonly observed among thermally-induced λ lysogen cultures, is a reflection of the saltatory nature of individual lysis events at the microscopic level. However, it is not clear to what extent Z-VAD-FMK mouse the seemingly high synchronicity of lysis is influenced by various aspects of phage biology and host growth conditions. In this study, we used a simple experimental setup to assess how lysis time stochasticity is affected by allelic variation in the S protein, late promoter p R ‘ activity, host growth rate,

and the timing of energy poison KCN addition. Our results establish the ranges and limits of lysis time stochasticity under various conditions. Results Using a microscope-mounted, temperature-controlled perfusion chamber, we observed and recorded individual lysis events of thermally-induced Escherichia coli l lysogens (Figure 2A). These observations revealed a considerable amount of variation in lysis time for the wild-type Rho (WT) λ phage (Table 1; Figure 2B). Although

the mean lysis time for the WT λ phage was 65.1 min, lysis times for individual lysogenic cells ranged from 45.4 to 74.5 min. Given that phage progeny accumulate linearly at ~7.7 phage per minute beginning ~28 min after lysis induction [46], the ~30 min range of lysis times could result in a three-fold difference in burst size between phages that lyse early and those that lyse late. This result motivated further exploration of variation in lysis time among other λ strains. Table 1 Effects of holin allelic sequences on the stochasticity of lysis time. Strain n a MLT (min) SD (min) IN61 274 45.7 2.92 IN56 (WT) 230 65.1 3.24 IN160 47 29.5 3.28 IN62 136 54.3 3.42 IN70 52 54.5 3.86 IN57 53 47.0 4.25 IN69 119 45.0 4.38 IN63 209 41.2 4.55 IN64 63 48.4 4.60 IN68 153 54.1 5.14 IN66 189 82.2 5.87 IN67 212 57.6 6.71 IN65 33 83.8 6.95 IN71 49 68.8 7.67 a In some cases, the sample size n is the pooled number of cells observed across several days. Detailed information can be found in Table S1 of additional file 1. Figure 2 Samples of a lysis recording and frequency distributions of various experimental treatments. (A) Sample recordings from strain IN63. It takes about 5 sec for the upper left cell to HKI272 disappear from view.