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
Pichia membranifaciens strain FY-101, isolated from grape skins, was found to be antagonistic to Botrytis cinerea, the causal organism of the grey mould disease of the grapevine. When grown together on solid as well as liquid media, the yeast brings about the inhibition of this parasitic fungus, coagulation and leakage of its cytoplasm, and suppression of its ability to produce the characteristic grey mould symptoms on the grapevine plantlets. In vitro experiments confirm that this yeast can be used as a biological control organism against B. cinerea. An account of the molecular characterisation of P. membranifaciens (complete sequence of the ITS region of its ribosomal DNA, GenBank accession No. AF 270935), as well as the interaction between B. cinerea and the yeast, are given here.