Isolation of adherent polycyclic aromatic hydrocarbon (PAH)-degrading bacteria using PAH-sorbing carriers

Two different procedures were compared to isolate polycyclic aromatic hydro carbon (PAH)-utilizing bacteria from PAH-contaminated soil and sludge sampl es, i.e., (i) shaken enrichment cultures in liquid mineral medium in which PAHs were supplied as crystals and (ii) a new method in which PAH degraders were enriched on and recovered from hydrophobic membranes containing sorbe d PAHs. Both techniques were successful, but selected from the same source different bacterial strains able to grow on PAHs as the sole source of carb on and energy. The liquid enrichment mainly selected for Sphingomonas spp,, whereas the membrane method exclusively led to the selection of Mycobacter ium spp. Furthermore, in separate membrane enrichment set-ups with differen t membrane types, three repetitive extragenic palindromic PCR-related Mycob acterial strains were recovered. The new Mycobacterium isolates were strong ly hydrophobic and displayed the capacity to adhere strongly to different s urfaces. One strain, Mycobacterium sp. LB501T, displayed an unusual combina tion of high adhesion efficiency and an extremely high negative charge. Thi s strain may represent a new bacterial species as suggested by 16S rRNA gen e sequence analysis. These results indicate that the provision of hydrophob ic sorbents containing sorbed PAHs in the enrichment procedure discriminate d in favor of certain bacterial characteristics. The new isolation method i s appropriate to select for adherent PAM-degrading bacteria, which might be useful to biodegrade sorbed PAHs in soils and sludge.