Diazotrophic endophytic bacteria enhance plant growth through biological nitrogen fixation and production and release of plant growth regulating substances, which facilitate the revegetation of areas degraded by human activities. However, little is known about populations of such bacteria in soils or plants of mining areas. Aiming to study the effects of different vegetation types and rehabilitation periods on some endophytic diazotrophic bacteria species, soil samples were collected under two environmental conditions ("Campo" and "Serra") in bauxite mined areas undergoing different rehabilitation processes. Population densities were evaluated by the most probable number method in media (NFb, JNFb, and Fam for Azospirillum brasilense and A. lipoferum, Herbaspirillum spp. and A. amazonense, respectively) and ranged from 0 to 2.0 x 10(4) bacteria g-1 soil. The vegetation types affected the diazotrophic populations. Highest densities were found in mined soils revegetated with the grass species brachiaria (Brachiaria decumbens), rye grass (Lolium multiflorum) and capim-gordura (Melinis minutiflora). However, these densities are considered low compared to those found in agricultural soils. No relationship was found between the rehabilitation time and population density. Thirty-six cultural phenotypes were found on potato medium among 72 isolates out of all three culture media. At a similarity of at least 63 %, these isolates formed seven great groups, five of which (comprising 62.5 % of the total isolates) contained the type strains of Burkholderia brasilensis, Herbaspirillum seropedicae, and Azospirillum spp. (A. brasilense, A. amazonense, A. lipoferum, A. irakense). In spite of its low density, this group of bacteria presented a high phenotypic diversity in the studied environment.
Azospirillum spp.; Herbaspirillum; Burkholderia; biological nitrogen fixation; grasses
