DGGE analysis of PCR-amplified nifH gene fragments generated with DNA from Dutch and Brazilian bulk and rhizosphere soil samples and individual P. azotofixans strains. Lane 1, Ede loamy sand bulk soil; lane 2, Flevo silt loam bulk soil; lane 3, Guaíra bulk soil; lane 4, Cerrado soil, maize rhizosphere, 30 days; lane 5, Cerrado soil, maize rhizosphere, 60 days; lane 6, Várzea soil, maize rhizosphere, 10 days; lane 7, Várzea soil, maize rhizosphere, 30 days; lane 8, Várzea soil, maize rhizosphere, 60 days; lane 9, Várzea soil isolate LV17; lane 10, Várzea soil isolate PV55; lane 11, Várzea soil isolate PV18; lane 12, Várzea soil isolate PV9; lane 13, strain C3L4; lanes M, markers (16S rDNA-based products of [from top to bottom] Listeria innocua ALM105, Arthrobacter sp., and Burkholderia cepacia P2).