Azotobacters as biofertilizer

Document Outline

• Azotobacters as biofertilizer
  • Biofertilizers are important
  • The genus Azotobacter
  • Azotobacters can fix atmospheric nitrogen
  • Azotobacters produce plant hormones
  • Azotobacters can solubilize phosphates
  • Azotobacters are capable of suppressing phytopathogens or reduce their deleterious effect
  • Use of Azotobacters as biofertilizers dates back to almost a century and two decades
  • Methods of application of Azotobacters
  • The chromosomes of Azotobacters
    • Azotobacters contain multiple copies of the chromosome
    • Construction of mutants of Azotobacters
  • The enzyme that converts nitrogen into ammonia
  • Protection of nitrogenase from oxygen in Azotobacters
  • DNA gyrase is necessary for nitrogen fixation by Azotobacter vinelandii
  • Genes coding for the three polypeptides of the enzyme nitrogenase
  • Alternative pathways of nitrogen fixation in Azotobacters
  • Genes of the constituents of the molybdenum dependent pathway of nitrogen fixation in A. vinelandii
  • Genes of the constituents of the vanadium dependent pathway of nitrogen fixation in A. vinelandii
  • Genes of the constituents of the anf pathway of nitrogen fixation in A. vinelandii
  • Effect of molybdenum and vanadium ions on transcription of the structural genes of nitrogenases of the three pathways
  • The promoters of the operons containing the genes involved in nitrogen fixation in Azotobacters
  • Upstream activator binding site
  • Expression of the nifLA operon of A. vinelandii is an enigma
  • Interaction of NifL and NifA
  • Maximizing nitrogen fixation and excretion of ammonia by Azotobacters
    • Insertion in vivo of the kanamycin resistance cassette into the nifL gene of A. vinelandii
    • Deletion of the nifL gene and continuation of expression of the nifA gene from the native nifLA promoter
    • Deletion of the nifL gene and insertion of the Tet promoter there
    • Mutagenesis of nifA to make NifA resistant to inhibition by NifL
    • Introducing a plasmid containing the nifH gene into A. vinelandii
    • Engineering of genes other than those associated with the nif complex
  • Use of genetically engineered Azotobacters as biofertilizers
    • Azotobacter with enhanced phosphate solubilizing capability
    • Azotobacter with enhanced capacity to excrete fixed nitrogen
    • Azotobacter that consumes less ammonia
    • A. chroococcum with its nifL gene deleted and its nifA gene under the control of the Tet promoter from the plasmid ...
  • Concluding remarks
  • References