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

Recent reports suggest that Mycobacterium is better, adapte to soils containing poorly bioavailable polycyclic aromatic hydrocarbons (PAHs) compared to Sphingomonas. To study this hypothesis, artificial conditions regarding PAH bioavailability were induced in two PAH-contaminated soils and the response of the eubacterial, Mycobacterium, and Sphingomonas communities to these changed conditions was monitored during laboratory incubation. SoilK3663 with a relatively high proportion of high molecular weight PAHs was amended with phenanthrene or pyrene to artificially change the soil into a soil,with a relatively increased bioavailable, PAH contamination. Soil AndE with, a, relatively high proportion of bioavailable low molecular weight,, PAHs was treated by a single-step Tenax extraction to remove the largest part of the easily,bioavailable PAH contamination. In sod K3663, the added phenanthrene or pyrene compounds were, rapidly degraded, concomitant with a significant increase in the, number of phenanthene and pyrene degraders, and minor and, no changes in the Mycobacterium community and Sphingomonas community respectively. However, a transient change in the eubacterial community related to the proliferation of several gamma-protcobacteria was noted in the, phenanthrene-amended soil. In, the extracted AndE soil,: the Sphingpmonas community initially developed into a more diverse 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 gamma-protcobacterial population. The results suggest that the relative, bioavallability of PAH contamination in soil affects bacterial community structure but that the behavior of Mycobacterium and Sphingpmonas in soil is more complex than prospected from studies on their ecology and physiology.