Fig. 1 Denaturing gradient gel electrophoresis gel of Bacteria 16S rDNA polymerase chain reaction (PCR) products (Bases 338 to 518 relative to the E. coli rRNA sequence) amplified from USA (Lanes 2–6) and Norwegian (Lanes 7–8) soil-DNA extracts. Gel gradient ranging from 30 to 55% denaturant. Lane 1, marker (PCR products from top to bottom, Pseudomonas putida, Acinetobacter sp. ADP1, Comamonas acidovorans ATCC 15668, E. coli DH5, Alcaligenes sp. BR40, C. testosteroni); Lane 2, PAH (700 mg kg^-1)–contaminated soil; Lane 3, no-till corn field; Lane 4, no-till soybean field; Lane 5, plowed corn field; Lane 6, plowed soybean field; Lane 7, fallow field; Lane 8, pastureland. Arrows indicate the dominant populations (Lane 2) and regions of greater band intensity that characterize the community structure (Lanes 3, 4 and 7). Minus signs indicate intense bands not seen in Lanes 4–6 but present in Lane 3