Differential responses of eubacterial, mycobacterium, and Sphingomonas communities in polycyclic aromatic hydrocarbon (PAH)-contaminated soil to artificially induced changes in PAH profile

Recent reports suggeat that Mycobacterium is better adapted to soils containing poorly bioavailable polycyclic aromatic hydrocarbons (PAHs) compared to Sphingomonas. To study this hypothesis, artificial conditions regarding PAH proflle and PAH bioavailability were induced in two PAH-contaminated soils and the response ofthe eubacterial, Mycobacterium, and Sphingomonas communities to these changed conditions was monitored during labotatotyincubation. Soil K3663witharelativelyhighproportion of high moletular weight PAHs was amended with phenanthrene or pyrene to artificially change the soil into a soil with a relatively increased bloavailable PAH contamination. Soil AndE with a relatively high ptoportion of bioavailable low mulecular weight PAHs was treated by a single-step Tenat extraction to remove the largest part of the easily bioavailable PAH contamination. In soil K3663, the added phenanthrene or pytene compounds were rapidiy degraded, concomitant with a significant increase in the number of phenanthrene and pyrene degraders, and minor and no changes in the Mycobacterium community and Sphingomonas community, respoctively. However, a transient change in the eubactenal community related to the proliferation of several γ-proteobacteria was noted in the phenanthrene-amended soil. In the extracted AndE soil, the Sphingomonas community initially developed into a more divetse community but finally decreased in size below the detection limit. Mycobacterium in that soil never increased to a detectable size, while the eubacterial community became dominated by a γ-proteobacterial population. The results suggest that the relative bioavailability of PAH contamination in soil affects bacterial community structure but that the behavior of Mycobacterium and Sphingomonas in soil is more complex than prospected from studies on their ecology and physiology.