Physical characterization of nif structural genes in azotobacter and azospirillum spp.

Abstract

The ability to fix atmospheric nitrogen of some microorganism was involved with the nitrogenase and the genetic expression of nitrogen fixation genes. A little knowledge on the nitrogen fixation genes of Azotobacter and Azospirillum is known. So, as a fundamental research for genetic improvement of nitrogen fixing bacteria which was isolated from Thai source, localization in and physical characterization of nitrogenase structural genes were studies in five strains of Azotobacter and four strains of Azospirillum spp. No plasmid was detected in all strains of Azotobacter spp. Whereas one to four molecular species of plasmid ranging approximately from 9 to 100 Kb in size were detected in three strains of Azospirillum spp., and these plasmids did not carry nitrogenase structural genes. Restriction endonuclease patterns showed discrete bands and reproducible differences among the species and strains of Azotobacter and Azospirillum. This result indicated that very high reiterated sequences were found in the chromosome of Azotobacter and Azospirillum spp. Thus, we suggested that the restriction endonuclease patterns may be used to identify the strains of Azotobacter and Azospirillum spp. Southern blot hybridization between [Superscript 32]p-pSA 30 which carrying nitrogenase structural genes of Klebsiella pneumoniae M5al and restriction fragments of Azotobacter or Azospirillum chromosome showed that nitrogenase structural genes of the nine strains located on their located on their chromosomes, Moreover, the hybridization patterns showed many differences among all strains examined. This preliminary study illustrated that the organization of nitrogenase structural genes were differences among these strains. Degree of homology was detected between nif H, nif D and nif K of Klebsiella pneumoniae and nitrogenase structural genes of Azotobacter or Azospirillum by Dot blot hybridization techniques. The homology was found limited only nif H and nif D of Azospirillum DNA whereas the homology was observed with nif H and nif D of Azospirillum DNA whereas the homology was observed with nif H, nif D and also nif K in all strains of Azotobacter spp.