Partial characterization of nif genes from the bacterium Azospirillum amazonense

Azospirillum amazonense revealed genomic organization patterns of the nitro gen fixation genes similar to those of the distantly related species A. bra silense. Our work suggests that A. brasilense nifHDK, nifENX, fixABC operon s and nifA and glnB genes may be structurally homologous to the counterpart genes of A. amazonense. This is the first analysis revealing homology betw een A. brasilense nif genes and the A. amazonense genome. Sequence analysis of PCR amplification products revealed similarities between the amino acid sequences of the highly conserved nifD and glnB genes of A. amazonense and related genes of A. brasilense and other bacteria. However, the A. amazone nse non-coding regions (the upstream activator sequence region and the regi on between the nifH and nifD genes) differed from related regions of A. bra silense even in nitrogenase structural genes which are highly conserved amo ng diazotrophic bacteria. The feasibility of the 16S ribosomal RNA gene-bas ed PCR system for specific detection of A. amazonense was shown. Our result s indicate that the PCR primers for 16S rDNA defined in this article are hi ghly specific to A. amazonense and can distinguish this species from A. bra silense.