High relatedness among interacting individuals has generally been considered a precondition for the evolution of altruism. However, kin-selection theory also predicts the evolution of altruism when relatedness is low, as long as the cost of the altruistic act is minor compared to its benefit. Here, we demonstrate evidence for a low-cost altruistic act in bacteria. We investigated Escherichia coli responding to the attack of an obligately lytic phage by committing suicide in order to prevent parasite transmission to nearby relatives. We found that bacterial suicide provides large benefits to survivors at marginal costs to committers. The cost of suicide was low because infected cells are moribund, rapidly dying upon phage infection, such that no more opportunity for reproduction remains. As a consequence of its marginal cost, host suicide was selectively favoured even when relatedness between committers and survivors approached zero. Altogether, our findings demonstrate that low-cost suicide can evolve with ease, represents an effective host-defence strategy, and seems to be widespread among microbes. Moreover, low-cost suicide might also occur in higher organisms as exemplified by infected social insect workers leaving the colony to die in isolation.
readme.txt
Contains descriptions of all data files.
120308b_2.pda
File: 120308b_2.pda
Format: SoftMax Pro 5.42.1.0 (Molecular Devices, Sunnyvale, CA)
Contents: Measurements of optical density of bacterial cultures. Rows A-D contain cultures of E. coli lambda, rows E-H contain cultures of E. coli HK97. Columns 1 and 2 contain uninfected cultures. Columns 3-11 contain cultures that were infected with 5x10^0 - 5x10^8 pfu of phage T4rII. Column 12 contains blanks (medium only).
120308b_2.txt
File: 120308b_2.txt
Format: text
Contents Measurements of optical density of bacterial cultures
Note: Same data as in file 120308b_2.pda
figure1_r_script.r
File: figure1_r_script.r
Format: r source file
Contents: reads in all growth data, calculates doubling times, calculates statistics, plots figure 1 to pdf
Note: requires package nlstools
intrinsic_costs.zip
Files: intrinsic_costs.zip (contains files well.XXX (XXX are numbers from 001 to 096))
Format: ZIP archive (contents are flow cytometry data files FCS 2.0)
Contents: Flow cytometry analyses of bacterial cultures. Samples were excited at a wavelength of 488 nm, while emission was detected at 510 nm (GFP) and 560 nm (DsRed).
120524_exp390.csv
File: 120524_exp390.csv
Format: text (comma separated values)
Contents: Data obtained from the analysis of all flow cytometry data files in intrinsic_costs.zip using WEASEL 3.0.1. Files also contains information about the identity of every sample.
intrinsic_costs_r_script.r
File: intrinsic_costs_r_script.r
Format: r source file
Contents: reads in all flow cytometry data and calculates statistics
intrinsic_costs_r_script.R
120524_1.pda
File: 120524_1.pda
Format: SoftMax Pro 5.42.1.0 (Molecular Devices, Sunnyvale, CA)
Contents: Measurements of optical density of bacterial cultures. Cultures in rows A, C, E, and G contain treatments without phage T4rII, cultures in rows B, D, F, and H contain treatments with phage T4rII. E. coli lambda was labelled with pDsRed in columns 1, 3, 5, 7, 9, and 11. E. coli lambda was labelled with pGFP in columns 2, 4, 6, 8, 10, and 12. The initial frequency of E. coli lambda was 99.9% in cultures in columns 1 and 2, 99% in cultures in columns 3 and 4, 95% in cultures in columns 5 and 6, 90% in cultures in columns 7 and 8, 50% in cultures in columns 9 and 10, and 10% in cultures in columns 11 and 12.
120524_1.txt
File: 120524_1.txt
Format: text
Contents Measurements of optical density of bacterial cultures
Note: Same data as in file 120524_1.pda
figure2.zip
Files: figure2.zip (contains files well.XXX (XXX are numbers from 079 to 108 and from 301 to 396))
Format: ZIP archive (contains flow cytometry data files FCS 2.0)
Contents: Flow cytometry analyses of bacterial cultures. Samples were excited at a wavelength of 488 nm, while emission was detected at 510 nm (GFP) and 560 nm (DsRed).
120525_exp391.csv
File: 120525_exp391.csv
Format: text (comma separated values)
Contents: Data obtained from the analysis of flow cytometry data files well.301 - well.396 using WEASEL 3.0.1. File also contains information about the identity of every sample. Data are from samples taken after the competition experiment.
120524_97-108.csv
File: 120524_97-108.csv
Format: text (comma separated values)
Contents: Data obtained from the analysis of flow cytometry data files well.079 - well.108 using WEASEL 3.0.1. File also contains information about the identity of every sample. Data are from samples prior to the competition experiment and are used to obtain the initial frequencies of the competitors as shown on the x-axis of the inset of figure 2 and on the right side of figure 2.
figure2_r_script.R
File: figure2_r_script.r
Format: r source file
Contents: reads in all growth data, reads in all flow cytometry data, calculates statistics, plots figure 2 to pdf
Note: requires package dichromat
figure3.zip
Files: figure3.zip (contains files well.XXX (XXX are numbers from 001 - 096, from 101 to 196, and from 201 to 204))
Format: ZIP archive (contains flow cytometry data file FCS 2.0)
Contents: Flow cytometry analyses of bacterial cultures. Samples were excited at a wavelength of 488 nm, while emission was detected at 510 nm (GFP) and 560 nm (DsRed).
120525_exp392b.csv
File: 120525_exp392b.csv
Format: text (comma separated values)
Contents: Data obtained from the analysis of flow cytometry data files well.101 - well.196 and well.201 - well.204 using WEASEL 3.0.1. File also contains information about the identity of every sample. Data are use to produce figure 3a.
120525_exp392a.csv
File: 120525_exp392a.csv
Format: text (comma separated values)
Contents: Data obtained from the analysis of flow cytometry data files well.001 - well.096 and well.201 - well.202 using WEASEL 3.0.1. File also contains information about the identity of every sample. Data are used to produce figure 3b.
figure3_r_script.r
File: figure3_r_script.r
Format: r source file
Contents: reads in all growth data, reads in all flow cytometry data, calculates statistics, plots figure 3a and 3b to pdf
Note: requires package dichromat
figure3_r_script.R