Diversity of free-living nitrogen-fixing bacteria associated with Korean paddy fields

Abstract

Nitrogen (N)-fixing microorganisms play a major role in maintaining soil fertility and are thereby important for sustainable rice production. Among a total of 165 bacterial isolates recovered from seven paddy field soils through an isolation process on four N-free media, 32 were found to be positive for PCR amplification of nifH gene. On screening, the BOX-PCR fingerprint technique grouped the nifH gene positive isolates into seven clusters. Clustering of bacteria revealed a very low level of similarity (20%), indicating the existence of a high degree of genetic diversity among the N-fixing isolates. Further characterization based on fatty acid methyl ester (FAME) showed that the isolates were members of 16 different genera, with maximum number belonged to the genus Burkholderia followed by Sphingomonas. Our results provide evidence for wide diversity of free-living N-fixing bacteria that can be used in future as a feasible alternative to N fertilizers in rice-paddy ecosystems. © 2012 Springer-Verlag and the University of Milan.