Modeling fitness for damage partitioning in bacteria.

Results report relative fitness over time for populations propagated in a computer model as described (Methods). Parameter values of λ = .0095 min^-1 and Π = 18.30 min were used for all simulations. A relative fitness of .5 corresponds to a severely damaged and effectively dead cell that no longer can divide. Because fitness stabilizes after about 1500 min with these parameter values, fitness values between 1500 to 5000 min were used to calculate mean fitness. (A) Relative fitness over time for asymmetrical partitioning with stochasticity (a = .48; var = σ_S² = .00046); symmetrical partitioning with stochasticity (a = ½; var = σ_S² = .00046); and symmetrical partitioning with no stochasticity (a = .5; var = 0). (B) Relative fitness over time for asymmetrical partitioning with stochasticity (a = .48; var = σ_S² = .00046; no anchored damage); symmetrical partitioning with elevated stochasticity (a = ½; var = σ_S² + D²/4 = .00046 + .0004²/4 = .00086; no anchored damage); asymmetrical partitioning with stochasticity (a = .48; var = σ_S² = .00046; with anchored damage C = .05); symmetrical partitioning with elevated stochasticity (a = ½; var = σ_S² + D²/4 = .00046 + .0004²/4 = .00086; with anchored damage C = .05). (C) Anchored damage in asymmetrically produced daughters. Because asymmetrical partitioning (gray shading) allocates movable damage to the old daughter and anchored damage (_*) is more likely to appear first in the mother’s older pole, the difference between old and new daughters is magnified. The magnification increases the variance of damage partitioning. (D) Anchored damage in symmetrically produced daughters. If partitioning is symmetric but stochastic, 50% of the time movable damage is allocated to the old daughter as in Fig 4C. However the other 50% of the time it is as depicted here, where movable damage (gray shading) is allocated to the new daughter and anchored damage (_*) is in the old daughter. The old and new daughters are rendered more similar and the variance of damage partitioning is reduced.