ABSTRACT
In order to understand the effect of the maize rhizosphere on denitrification, the diversity and the activity of the denitrifying community were studied in soil amended with maize mucilage. Diversity of the denitrifying community was investigated by polymerase chain reaction (PCR) amplification of total community DNA extracted from soils using gene fragments, encoding the nitrate reductase (narG) and the nitrous oxide reductase (nosZ), as molecular markers. To assess the underlying diversity, PCR products were cloned and 10 gene libraries were obtained for each targeted gene. Libraries containing 738 and 713 narG and nosZ clones, respectively, were screened by restriction fragment analysis, and grouped based on their RFLP (restriction fragment length polymorphism) patterns. In all, 117 and 171 different clone families have been identified for narG and nosZ and representatives of RFLP families containing at least two clones were sequenced. Rarefaction curves of both genes did not reach a clear saturation, indicating that analysis of an increasing number of clones would have revealed further diversity. Recovered NarG sequences were related to NarG from Actinomycetales and from Proteobacteria but most of them are not related to NarG from known bacteria. In contrast, most of the NosZ sequences were related to NosZ from alpha, beta, and gammaProteobacteria. Denitrifying activity was monitored by incubating the control and amended soils anaerobically in presence of acetylene. The N2O production rates revealed denitrifying activity to be greater in amended soil than in control soil. Altogether, our results revealed that mucilage addition to the soil results in a strong impact on the activity of the denitrifying community and minor changes on its diversity.
Subject(s)
Bacteria/classification , Bacteria/metabolism , Biodiversity , Polysaccharides/metabolism , Soil Microbiology , Zea mays/metabolism , Actinomycetales/classification , Actinomycetales/genetics , Actinomycetales/isolation & purification , Actinomycetales/metabolism , Bacteria/genetics , Bacteria/growth & development , Bacteria/isolation & purification , Cloning, Molecular , DNA, Bacterial/analysis , DNA, Bacterial/isolation & purification , Gene Library , Molecular Sequence Data , Nitrate Reductase , Nitrate Reductases/analysis , Nitrate Reductases/chemistry , Nitrate Reductases/genetics , Nitrous Oxide/metabolism , Oxidoreductases/analysis , Oxidoreductases/chemistry , Oxidoreductases/genetics , Plant Roots/metabolism , Plant Roots/microbiology , Polymerase Chain Reaction , Polymorphism, Restriction Fragment Length , Proteobacteria/classification , Proteobacteria/genetics , Proteobacteria/isolation & purification , Proteobacteria/metabolism , Sequence Analysis, DNA , Zea mays/microbiologyABSTRACT
The acclimatisation of an activated sludge to enhanced biological phosphorus removal conditions was followed after and without bioaugmentation with a low amount of phosphorus-accumulating sludge. Phosphorus removal yields were monitored by conventional analytical methods and microbial communities evolutions were followed by a finger printing molecular technique (PCR-SSCP). While the benefit of the bioaugmentation seems real at the level of the reactor parameters, bioaugmentation speeded up the installation of good and stable phosphorus removal yield, the establishment of the inoculated microbial community in the bioaugmented reactor is still unclear. Both the bioaugmented and the control microbial communities evolved in a similar way to end up with apparently comparable populations. At the time of the experiment, the results suggest that the microbial community inoculated for the bioaugmentation did not establish in the reactor but compensated for phosphorus accumulation until the acclimatisation of an endogenous microbial community arose.