CLONING AND SEQUENCING OF THE NITROGENASE STRUCTURAL GENES NIFHDK OF HERBASPIRILLUM-SEROPEDICAE

The nitrogenase structural genes (nifHDK) of the endophytic diazotroph Herbaspirillum seropedicae were isolated from a genomic bank by plate hybridization. Sequence analysis of the DNA showed a consensus promot er region upstream from the nifH gene containing a -24/-12 type promot er together with NifA- and integration host factor (IHF)-binding sites . The derived protein sequences of NifH, NifD and NifK contained conse rved cysteine residues for binding iron-sulfur clusters and the iron-m olybdenum cofactor. These protein sequences showed the strongest simil arities to the nifHDK gene products of the symbiotic diazotroph Bradyr hizobium japonicum (93.5%, 91.3% and 83.3%, respectively), the plant-a ssociated diazotroph Azospirillum brasilense (90.0%, 83.7% and 75.1%, respectively) and to Thiobacillus ferrooxidans (91.0%, 83.4% and 81.1% , respectively) of the same phylogenetic group of the protobacteria.