Bioavailability of clay-adsorbed dioxin to Sphingomonas wittichii RW1 and its associated genome-wide shifts in gene expression

Polychlorinated dibenzo-p-dioxins and dibenzofurans are a group of chemcially-related pollutants categorically known as dioxins. We used Sphingomonas wittichii strain RW1 (RW1), one of the few strains able to grow on dioxin, to characterize its ability to respond to and degrade clay-bound dioxin. Strain RW1 grew on and completely degraded dioxin intercalated in smectite clay. To characterize the effects of sorption and bioavailability of dioxin on RW1, transcriptomes of RW1 either grown with dioxin intercalated to clay (DDSAP) or with free crystalline dioxin (DD) were sequenced using RNA-Seq. While either condition caused RW1 large-scale shifts in gene expression compared to succinate control (SUC), differences in gene expression between these two conditions were marked by a small number (86) of differentially expressed genes. The differences in gene expression may reflect the underlying adaptive mechanisms by which RW1 cells sense and deploy pathways to access dioxin intercalated in the clay. Transcriptomes were sampled in triplicate (3 biological replicates) at early to mid log phase from cultures grown under three different conditions: succinate (SUC), dibenzo-p-dioxin (DD), and clay-sorbed dibenzo-p-dioxin (DDSAP).