Single-cell Analysis of λ Immunity Regulation

Bæk, Kristoffer T.; Svenningsen, Sine Lo; Eisen, Harvey; Sneppen, Kim; Brown, Stanley

doi:10.1016/j.jmb.2003.09.037

Cited by 52 publications

(26 citation statements)

References 34 publications

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“…As expected, a low number of phages were observed in both the arabinose-induced and uninduced cultures of the single lysogen. About half of the phages formed clear plaques, indicating that induction was primarily the result of mutation (17). Similar results were obtained for the uninduced culture of the triple lysogen.…”

Section: Premature Q Expression Promotes Lytic Developmentsupporting

confidence: 79%

“…The number of prophage copies in SY822() (17) and MG1655(pSEM3058) cells was determined by real-time quantitative PCR (qPCR) using two primer sets targeting and E. coli DNA, respectively, as described for determination of bacterial plasmid copy number (9). Briefly, total DNA from bacterial cells was purified with the PureLink genomic DNA minikit (Invitrogen), and the DNA concentration was measured on a NanoDrop spectrophotometer (Thermo Scientific) and adjusted to 19 ng/l.…”

Section: Methodsmentioning

confidence: 99%

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Commitment to Lysogeny Is Preceded by a Prolonged Period of Sensitivity to the Late Lytic Regulator Q in Bacteriophage

Svenningsen

Semsey

2014

Journal of Bacteriology

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A key event in development is the irreversible commitment to a particular cell fate, which may be concurrent with or delayed with respect to the initial cell fate decision. In this work, we use the paradigmatic bacteriophage lysis-lysogeny decision circuit to study the timing of commitment. The lysis-lysogeny decision is made based on the expression trajectory of CII. The chosen developmental strategy is manifested by repression of the pR and pL promoters by CI (lysogeny) or by antitermination of late gene expression by Q (lysis). We found that expression of Q in trans from a plasmid at the time of infection resulted in a uniform lytic decision. Furthermore, expression of Q up to 50 min after infection results in lysis of the majority of cells which initially chose lysogenic development. In contrast, expression of Q in cells containing a single chromosomal prophage had no effect on cell growth, indicating commitment to lysogeny. Notably, if the prophage was present in 10 plasmid-borne copies, Q expression resulted in lytic development, suggesting that the cellular phage chromosome number is the critical determinant of the timing of lysogenic commitment. Based on our results, we conclude that (i) the lysogenic decision made by the CI-Cro switch soon after infection can be overruled by ectopic Q expression at least for a time equivalent to one phage life cycle, (ii) the presence of multiple chromosomes is a prerequisite for a successful Q-mediated switch from lysogenic to lytic development, and (iii) phage chromosomes within the same cell can reach different decisions.

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Section: Premature Q Expression Promotes Lytic Developmentsupporting

confidence: 79%

Section: Methodsmentioning

confidence: 99%

Commitment to Lysogeny Is Preceded by a Prolonged Period of Sensitivity to the Late Lytic Regulator Q in Bacteriophage

Svenningsen

Semsey

2014

Journal of Bacteriology

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“…In reality, it is quite likely that a cross-infection only affects the decision if it occurs within a short time window after the first infection, in which case the number of cross infected bacteria is likely to be negligible. Finally, we assume that spontaneous induction of lysogens happens very rarely [≤ 10 −5 /generation (Bæk et al, 2003)] and would not change the final steady-state much, so we ignore this process.…”

Section: Methodsmentioning

confidence: 99%

In silico Evolution of Lysis-Lysogeny Strategies Reproduces Observed Lysogeny Propensities in Temperate Bacteriophages

et al. 2017

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Bacteriophages are the most abundant organisms on the planet and both lytic and temperate phages play key roles as shapers of ecosystems and drivers of bacterial evolution. Temperate phages can choose between (i) lysis: exploiting their bacterial hosts by producing multiple phage particles and releasing them by lysing the host cell, and (ii) lysogeny: establishing a potentially mutually beneficial relationship with the host by integrating their chromosome into the host cell's genome. Temperate phages exhibit lysogeny propensities in the curiously narrow range of 5–15%. For some temperate phages, the propensity is further regulated by the multiplicity of infection, such that single infections go predominantly lytic while multiple infections go predominantly lysogenic. We ask whether these observations can be explained by selection pressures in environments where multiple phage variants compete for the same host. Our models of pairwise competition, between phage variants that differ only in their propensity to lysogenize, predict the optimal lysogeny propensity to fall within the experimentally observed range. This prediction is robust to large variation in parameters such as the phage infection rate, burst size, decision rate, as well as bacterial growth rate, and initial phage to bacteria ratio. When we compete phage variants whose lysogeny strategies are allowed to depend upon multiplicity of infection, we find that the optimal strategy is one which switches from full lysis for single infections to full lysogeny for multiple infections. Previous attempts to explain lysogeny propensity have argued for bet-hedging that optimizes the response to fluctuating environmental conditions. Our results suggest that there is an additional selection pressure for lysogeny propensity within phage populations infecting a bacterial host, independent of environmental conditions.

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“…For extremely low dosage (near zero), spontaneous lysis events not induced by UV irradiation become the strongest contributing factor to the failure rate. These failures come from other events, such as spontaneous RecA activity[9] and mutations to λ -phage[7]. At high radiation doses (not plotted, see [17]), the fraction of lysis does not saturate at one and instead begins falling with respect to UV dose.…”

Section: Experimental Testsmentioning

confidence: 99%

“…In the lysogenic pathway, the phage integrates its genome into that of the host microbe, becoming a prophage, but otherwise does not damage the cell. This lysogenic state is very stable[7]; however, an insult to the cell through, for example, starvation or exposure to ultra-violet (UV) radiation[8] can trigger a process known as prophage induction[9]: the prophage is excised from the cell's genome, and viral replication occurs leading to cell lysis. The most well-studied lysogenic system is the bacteriophage λ , or λ -phage, which infects Escherichia coli .…”

mentioning

confidence: 99%

λ-prophage induction modeled as a cooperative failure mode of lytic repression

2009

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We analyze a system-level model for lytic repression of λ-phage in E. coli using reliability theory, showing that the repressor circuit comprises 4 redundant components whose failure mode is prophage induction. Our model reflects the specific biochemical mechanisms involved in regulation, including long-range cooperative binding, and its detailed predictions for prophage induction in E. coli under ultra-violet radiation are in good agreement with experimental data.

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Single-cell Analysis of λ Immunity Regulation

Cited by 52 publications

References 34 publications

Commitment to Lysogeny Is Preceded by a Prolonged Period of Sensitivity to the Late Lytic Regulator Q in Bacteriophage

Commitment to Lysogeny Is Preceded by a Prolonged Period of Sensitivity to the Late Lytic Regulator Q in Bacteriophage

In silico Evolution of Lysis-Lysogeny Strategies Reproduces Observed Lysogeny Propensities in Temperate Bacteriophages

λ-prophage induction modeled as a cooperative failure mode of lytic repression

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