Fig. 2.

A, Bacillus subtilis colonizes the hydroponic roots of Arabidopsis thaliana seedlings but does not maintain its association when seedlings are transferred to minimal salts medium for continued incubation. Error bars = standard error of the mean; ** indicates P < 0.01. B, An unrooted phylogenetic tree showing the relationships between the 96 rhizosphere bacterial strains tested for their hydroponic association with A. thaliana roots. Isolates found to maintain their associations with A. thaliana roots at a level at least one log-fold higher than B. subtilis alone are shown in green. The outer ring of orange dots indicates the 22 isolates selected in the primary screen for further study.