Fig. 2

Experimental evolution setup. Two mutant strains deficient in pyoverdine production, pvdS_gene and pvdS_prom, were allowed to evolve independently from each other and under different conditions. pvdS_gene carries a single point mutation in pvdS, encoding the iron-starvation sigma factor PvdS, while pvdS_prom carries a single point mutation in the promoter region of pvdS. The six environments used for experimental evolution differed both in their level of spatial structure (unstructured | structured) and in their iron content (“iron low”: iron chelator only; “iron medium”: iron chelator + 1 μM FeCl₃; “iron high”: iron chelator + 40 μM FeCl₃). Each ancestral strain was serially transferred in each of the six media in threefold replication, resulting in a total number of 36 independently evolved populations. Image sources: Servier Medical Art (multiwell plate); depositphotos.com (bacteria)