Fig. 4.

Tolerance of evolved strains to oxidative stress in H₂O₂. Oxidative stress of strains evolved in the presence or absence of bacteria, co-culture evolved and control respectively, with reference to their ancestor, was determined by spotting cells from stationary phase cultures on different concentrations of H₂O₂. Growth was scored after 3 days. The results show that competition against bacteria led to the evolution of strains sensitive to oxidative stress. The arrangement of the colonies on the plates is shown on the right. Numbers on the column of the illustrative stamp represent passage numbers from which the colonies were isolated. Passage numbers 10 to passage numbers 80 and continuing on the fourth column with strains isolated after 90 passages and 100 passages respectively are shown. The second and third column shows the same orientation. A–B–C are from triplicate co-culture evolved lines whereas D–E–F in brackets are from controls. For example lines A(D) means that colonies were either from flask A (co-culture evolved) or D (controls). “Anc” shows six positions of replicate colonies of the ancestral strain used as a reference.