Degradation of PAHs in soil by indigenous and inoculated bacteria

In soil heavily polluted by coal tar, the inherent mineralization of radio-labeled phenanthrene to {sup 14}CO{sub 2} was relatively slow, and a stimulation of degradation was observed by inoculation with a mixed population of PAH-degrading bacteria. A much faster inherent mineralization of phenanthrene was observed in soil slightly polluted by coal tar, and inoculation of this soil had no effect. Several phenanthrene-degrading bacteria were isolated from different soils. Two strains were further characterized as an Arthrobacter sp. and a Pseudomonas sp. In an organic medium without phenanthrene, growth rates of 0.52 h{sup {minus}1} and 0.71 h{sup {minus}1} were measured for the Arthrobacter sp. and the Pseudomonas sp., respectively. Most isolates grown in the phenanthrene-free medium, including the Arthrobacter sp., rapidly adapted to phenanthrene degradation following transfer to a phenanthrene-containing medium. In contrast, the phenanthrene-degrading capability of other strains, including the Pseudomonas sp., was lost during growth in the phenanthrene-free medium. Growth in an organic medium without phenanthrene of strains that retain the ability to degrade phenanthrene could prove to be a useful technique for production of PAH-degrading bacteria on a larger scale for soil inoculation.