Isolation and taxonomic affiliation of N-heterocyclic aromatic hydrocarbon-transforming bacteria.

The azaarenes (nitrogen-containing heterocyclic aromatic hydrocarbons) are products of incomplete combustion processes and thus are widely distributed with tar and oil products in the environment. Despite their adverse organoleptic, toxic, and carcinogenic characteristics, the biodegradability and fate of multi-ring azaarenes have received little attention. This work demonstrates the presence of genetically diverse azaarene-degrading bacteria in coal tar-contaminated soils. Thirty-eight bacterial strains able to transform the three-ring azaarenes, 5,6- and 7,8-benzoquinoline, phenanthridine, phenazine, or acridine, were isolated. Only seven of these strains grew in liquid medium on the specific azaarene compounds on which they were isolated using plates; and the rest transformed the azaarenes without growth. Taxonomic characterization by 16S ribosomal DNA sequencing revealed that our enrichment technique provided a diversity of 18 different azaarene-transforming bacterial species. Only a few strains were able to mineralize the homocyclic analogue, phenanthrene. Several of the isolates, e.g., Dyadobacter fermentans, Methylopila capsulata, and Agrobacterium tumefaciens, were related to genera relatively unknown with respect to the biodegradation of xenobiotic compounds. These strains can provide further information on the fate of azaarenes in the environment.

Bioaugmentation of tar-contaminated soils under field conditions using Pleurotus ostreatus refuse from commercial mushroom production.

The influence of the white rot fungus Pleurotus ostreatus on the degradation of selected poly- and heterocyclic aromatic hydrocarbons (referred to as polycyclic aromatic hydrocarbons [PAHs]) in soil was investigated under field conditions representing the Northern temperate zone. Pleurotus ostreatus was added to two contaminated soils in the form of homogenized refuse from the commercial production of fungus. The soils were collected from a former shipyard (the B&W soil) and underneath a former coal tar storage at an old asphalt factory in Denmark (the Ringe soil). Treatments (control, soil mixed with autoclaved sawdust medium, and soil mixed with P. ostreatus refuse) were set up in triplicate in concrete cylinders (height, 50 cm; diameter, 60 cm). The activity of P. ostreatus was measured as laccase activity and phenanthrene (PHE)- and pyrene (PYR)-degrading bacteria were enumerated. Twenty-one different PAHs were quantified. After nine weeks the concentrations of the 3-, 4-, 5-, and 6-ring PAHs in the Ringe soil were reduced by 78, 41, and 4%, respectively. These reductions corresponded with high initial laccase activity, a decrease in pH caused by the fungus, and an increase in the number of PHE- and PYR-degrading bacteria. No significant PAH degradation was observed in the B&W soil. Reasons for the difference in performance of P. ostreatus in the two soils are discussed in terms of soil histories and bioavailability. The use of P. ostreatus refuse holds promising potential for bioremediation purposes.