Figure 4.

Observed number of unique operational taxonomic units (OTUs; 97% sequence similarity) as a function of reduction in plasmid transfer frequency caused by metal stress. The OTU richness of the transconjugal pools (triangles) and the corresponding sorted soil recipient communities (diamonds) is shown. Experimental treatments (type of metal and degree of stress) are indicated; numbers refer to inhibitory concentrations decreasing [³H]leucine incorporation rates of the recipient bacterial community by 20% (IC₂₀) and 50% (IC₅₀).