Application of guaA gene, plasmid and strain in expression of azotobacter siderophore

The invention relates to the technical field of bioengineering, in particular to application of a guaA gene, a plasmid and a strain in expression of azotobacter siderophore. A guaA gene expression vector of nitrogen-fixing bacteria GXGL-4A is constructed by using a prokaryotic expression vector pET28a (+), the guaA gene expression vector is transformed into a wild strain GXGL-4A to obtain a positive transformed strain, and the strain can highly express siderophore by adding trace IPTG (isopropyl-beta-d-thiogalactoside) for induction during culture. Compared with the prior art, the siderophore yield of the azotobacter can be remarkably improved by expressing the guaA gene in the genome of the azotobacter, the obtained transformant can be used as a plant growth-promoting bacterium, absorption of iron in soil is increased on the basis of original nitrogen fixation, a plant root system is helped to obtain more iron elements from the soil and other environments, and the yield of siderophore is improved. Meanwhile,