Figure 2.

(a) Resistance to the pyocin S2. The surviving bacterial populations of O:9 that evolved in both iron-rich and -limited conditions, as well as the ancestral O:9 strain, were grown in the supernatant of PAO1 in order to test for resistance to the pyocin S2. All evolved populations displayed some form of resistance compared with the non-evolved ancestor, with bacterial populations evolved under iron limitation displaying lower levels of growth compared with populations grown in iron-rich conditions. Error bars represent the s.e.m. of four replicates from each population. (b) Evolved resistance is specific to pyocin S2. To rule out the effect of other growth-inhibiting compounds produced by the S2 pyocin producer PAO1, evolved bacterial populations and the non-evolved ancestor were grown in the supernatant of a S2 pyocin knockout mutant (PAO1150-2). Under these conditions, the non-evolved ancestor was able to grow, indicating that evolved resistance is indeed due to pyocin S2. Error bars represent the s.e.m. of four replicates from each population.