Fig. 6
Total cell numbers for different combinations of ancestral and evolved mutualistic partners from the B2 mutualistic consortium. Total cell numbers were measured as the OD600. Definitions: Panc, ancestral strain of BW25113 (∆proC); Tanc, ancestral strain of BW25113 (∆trpC); Pevol, evolved strain of BW25113 (∆proC); Tevol,a, evolved strain of BW25113 (∆trpC); Tevol,b, evolved strain of BW25113 (∆trpC). Tevol,a and Tevol,b are two genetically different strains of BW25113 (∆trpC) that emerged within the B2 mutualistic consortium. The data are presented as Tukey box plots. Note that the OD600 measurements (and thus cell density) were the largest for consortia containing the evolved ∆trpC partner, regardless of the evolutionary history of the ∆proC partner. Thus, mutations in only the ∆trpC partner are sufficient to explain the increase in OD600 over the course of the evolution experiment