Comparison of Nitrogen-fixing Bacterial Flora of Rice Rhizosphere in the Fields Treated Long-term with Agrochemicals and Non-agrochemicals

抄録

Nitrogen-fixing bacteria isolated from the rhizospheres of rice grown in a field treated long-term with agrochemicals (conventional farming; CF) and in a field free of agrochemicals (nature farming; NF) were compared by 16S rDNA sequencing. All of the bacteria isolated from rice grown in the NF field belonged to Actinomyces, α-Proteobacteria and β-Proteobacteria, while those from rice grown in the CF field belonged mainly to Actinomyces and α-Proteobacteria. Several species of β-Proteobacteria were also present in rice grown in the CF field. A group of nitrogen-fixing bacteria that showed 99.3%-98.3% similarity with Agromonas oligotrophica was present in samples from both fields, while other bacteria isolated from rice grown in the two fields differed in 16S rDNA. The nitrogen-fixing bacterium N32 showed 99.2% similarity with Burkholderia vietnamiensis, which is known to promote the growth of rice.