| The objectives of this study were to: (1) assess a collection of selected denitrifying strains in soils and surface sediments under grassland and cultivated soils; (2) determine genetic diversity among denitrifying bacteria in grassland and cultivated soil; and (3) evaluate the influence of conditions associated with soil depth and cultivation history on the occurrence of nitrate dissimilative abilities of Pseudomonas, Bacillus, and Enterobacter species obtained from grassland and cultivated soils. Konza Prairie Research Natural Area, a 3500-ha area dedicated to tallgrass prairie ecological research, provided an excellent opportunity to evaluate the proposed research objectives.; A polyphasic approach has been taken to assess a collection of selected denitrifying strains. Denitrifying bacteria were distributed into three Pseudomonas species: P. fluorescens, P. mephitica and P. putida. Repetitive sequence-based polymerase chain reaction (rep-PCR) using BOX A1R oligonucleotide primer, allowed distinction of denitrifying Pseudomonas spp. and differentiation of closely related strains within those species, suggesting this technique was the best method for grouping strains and measuring diversity in large collections.; Overall, the genetic diversity was estimated to be significantly greater on the surface than the genetic diversity of the total population. Bacterial species or biotypes did not vary between ecosystems, but the frequency of BOX-PCR types did vary within ecosystems. Only environmental conditions associated with soil depth affected genetic diversity of denitrifying fluorescent pseudomonads. The study of the distribution of facultative nitrate-reducing bacteria, including denitrifying bacteria, was also evaluated. The proportion of denitrifying bacteria increased significantly with depth, whereas the proportion of ammonia-producing nitrate reducers decreased significantly with depth at both grassland and cultivated sites. Environmental parameters associated with soil depth were the dominant factors in determining the species distribution. It is hypothesized that denitrification might be a selective advantage for denitrifying bacteria in the water-saturated zone and may have application for bioremediation. |
