Study On The Screening And Identification Of Siderophore-producing Bacteria And Its Effects On Growth-promoting Of The Tested Plants

In recent years,reduced crop yields because of iron deficiency,has become a key issue in global agricultural production.In the Northern China,soil salinization and alkalization are becoming more and more serious,leading to the scarcity of iron elements that can be absorbed and utilized by plants.Therefore,how to solve the problem of iron deficiency in plants is vital to agricultural industry.Microorganisms gradually evolved a mechanism during the evolution process,that is,they can secrete a siderophore,a kind of peptide which are able to bind specifically of Fe³⁺and forming a“siderophore-Fe³⁺”complex.Siderophore-producing bacteria is a collective name for a class of microorganisms that can produce siderophore.These bacteria work as a major class of plant rhizosphere probiotics.The siderophore produced by bacteria can specifically bind Fe³⁺and form a“siderophore-Fe³⁺”complex,which not only meets the needs of microorganisms,but also can be directly absorbed and utilized by plants,which provides a new idea to solve the problem of lack of iron.In this study,seven strains of siderophore-producing bacteria were isolated and screened from the rhizosphere soil of vegetables in Dingxi region of Gansu province,by using the method of microbial separation and screening technology,and CAS plate method was used as initial screening,quantitative detection of siderophore method as the rescreening method.Then,the strain with the largest diameter of the orange halo zone was selected to optimize its fermentation conditions through the shake flask fermentation test,and finally two high-yield siderophore-producing strains were obtained.And their effects on the indoor soil mesocosm ecosystem and their promoting effects on mung bean seedlings and Lolium multiflorum were studied.The main findings were as follows:Seven strains of siderophore-producing bacteria were isolated from the rhizosphere soil of vegetables and identified by the method of 16S rRNA molecules.They were Pseudomonas putida W7,Pseudomonas sp.W3,Pseudomonas mosselii LY5,Erwinia uzenensis E1,Klebsiella michiganensis WX9,Ochrobactrum pseudogrignonense LY15,Ochrobactrum pseudogrignonense E7.Fermentation tests were carried out on the two strains of E7 and W7with the largest diameter of the orange halo zone,and the results showed that the relative content of siderophore produced by strains E7 and W7 could reach 90.63%and 79.96%,respectively.The types of siderophore produced by two strains were hydroxamic acids by the tetrazolium salt test?MTT?.Through the indoor soil mesocosm ecosystem experiment,using sterile water as a blank control,the effect of inoculating siderophore-producing bacteria on soil ferrous ion content,siderophore relative content,microorganisms and enzyme activity was studied.The results showed that the treatment group of?E7+W7?was better than the single strain.After 35 days of treatment,compared with the control,the content of the available ferrous iron in soil?83.27%?,the relative content of siderophore?59.93%?,the activity of soil catalase?5.63%?,urease?38.78%?,alkaline phosphatase?48.22%?,invertase?42.17%?,the number of soil bacteria?35.73%?,fungi?20.15%?,and actinomycetes?40.14%?increased significantly by inoculating consortium of two strains?E7+W7?.The effects of strains inoculation on seed germination of Vigna radiata were studied by the method of petri dish germination with sterile water as the blank control.Treatment of the consortium of two strains diluted 100 times had the best effect on promoting the germination of Vigna radiata seeds.At 72 hours after germination,the seed vigor index of Vigna radiata seeds increased by 74.36%compared with the control.The growth promotion effects of siderophore-producing bacteria inoculation on Vigna radiata seedling and Lolium multiflorum under different iron ion concentrations were studied by pot experiment,with the uninoculated Hoagland nutrient solution as a blank control.The results showed that the consortium of two strains had a better effect than the single strain.The plant height,root length,fresh weight,dry weight,chlorophyll content,soluble protein content,and root FCR reductase activity of Vigna radiata seedlings increased by 47.25%,60.96%,62.11%,83.33%,41.46%,29.47%,80%,respectively,compared with the non-inoculated control;the best growth promoting effect on Lolium multiflorum was inoculated with consortium of two strains under medium concentration iron conditions?50?M?.At the same iron ion concentration,compared with the control,the plant height,root length,fresh weight,chlorophyll content,FCR reductase activity of Lolium multiflorum were increased,and leaf MDA content was reduced after treatment with consortium of two strains.At different iron ion concentrations,the biomass of Lolium multiflorum showed“low,medium iron concentration>high iron concentration>iron deficiency”,while the leaf MDA content changed the opposite.The results showed that low and medium iron concentration conditions were more suitable for the growth of Lolium multiflorum plants,and inoculation of siderophore-producing bacteria could maintain high biomass under iron-free and high iron stress.