Molecular cloning and physical mapping of the nitrogenase structural genes from the filamentous, non-heterocystous cyanobacterium Pseudanabaena sp. PCC7409

Sequences homologous to the structural genes for dinitrogenase (nifD and nifK) and nitrogenase reductase (nifH) have been cloned from the filamentous, non-heterocystous cyanobacterium Pseudanabaena PCC7409. The nifHDK^- homologous sequences were shown to reside on a 6.5-kb EcoRI restriction fragment by using a restriction fragment encoding the Klebsiella pneumoniae nifHDK genes as a heterologous hybridization probe. This 6.5-kb restriction fragment was cloned from a λ gt.wes EcoRI library of the Paseudanabaena sp. PCC7409 genome. This fragment was subcloned into the plasmid vector pUC9 to generate plasmid pPSU20. A detailed physical map of the insert in plasmid pPSU20 was determined, and relative positions of the nifH, nifD, and nifK homologous sequences on this fragment were determined by hybridization analysis with gene-specific fragments derived from the corresponding Anabaena sp. PCC7120 genes. The results indicate that these genes are contiguous in Pseudanabaena sp. PCC 7409 and are arranged in the order nifH, nifD, and nifK. This arrangement resembles that observed for other non-heterocystous cyanobacteria but differs from that observed for Anabaena, Calothrix, and Nostoc species.