Screening Of Siderophore-high-yield Plant Growth Promoting Rhizobacteria And Its Potential Application In Soil Remediation

The microbial-assisted phytoremediation is an emerging method in the remediation of heavy metal contaminated soil.In the remediation process,microorganisms or plant rhizosphere growth-promoting bacteria through secreting substances such as siderophores,HCN,and IAA,induce systemic resistance,and prevent pathogens to help plants survive and transfer heavy metals in contaminated soil.In addition to promoting plant growth,Siderophores also plays an important role in activating metals in the soil and reducing heavy metal toxicity.The paper studied the screening of Bacillus spp.which could be used for soil remediation,optimized the ferrum-producing medium and conditions,separated and purified the produced siderophore,and discussed its role in the remediation of heavy metals contaminated soil.It has certain theoretical significance and potential application value.The main research results of the paper are as follows:1)A siderophore-high-yield,Ni²⁺-resistant,and Pb²⁺-resistant plant growth promoting rhizobacteria were screened out from laboratory-preserved rhizobial Bacillus and identified as Bacillus tequilensis,named Bacillus tequilensis CD36.This strain can produce a variety of pro-biomass and is resistant to high concentrations of Ni²⁺and Pb²⁺.2)The medium and conditions of B.tequilensis CD36 were optimized through single-factor experiments to determine the optimal siderophore-producing fermentation conditions.For the modified MSA medium(g·L^-1):sucrose 15.0,glutamine 1.8,K₂HPO₄ 1.0 and MgSO₄.7H₂O0.5,pH 7.2,incubation temperature 26°C.In this condition,the 2,3-DHBA equivalent concentration of the siderophore of B.tequilensis CD36 was 1.17 mmol·L^-1,2.6 times before optimization.The culture supernatant was analyzed by LC-MS.The siderophore Bacillibacin and its three hydrolysates were found.And its monomer DHB-Gly-Thr was purified by two methods.In this research,the Fe?III?-IMAC method was used for the first time to purify the catechol-type siderophore,which provided a new method for the separation and extraction of catechol-type siderophores.3)Experiments showed that the order of chelation ability of the iron siderophore by B.tequilensis CD36 and experimental metal produced was:Fe³⁺?Pb²⁺?Ni²⁺?Al³⁺?Fe²⁺?Mn²⁺?Hg²⁺.Exploring the ability of siderophore to chelate various metals is conducive to further understanding the structure and function of siderophore and the development application of siderophore.4)Through the experiment of seed germination of Miscanthus,it was confirmed that siderophore plays a very important role in plant growth promoting rhizobacteria to relieve heavy metals Ni²⁺and Pb²⁺stress.When the concentration of siderophore is 0.8-1.2 mmol·L^-1,the siderophore can effectively relieve Ni²⁺and Pb²⁺stress in the environment and reduce the toxicity of heavy metals Ni²⁺and Pb²⁺to plant seeds.B.tequilensis CD36 has good growth-promoting ability.Its secreted siderophore can relieve Ni²⁺and Pb²⁺stress and toxic effects on Miscanthus seeds.Therefore,B.tequilensis CD36 has potential application value in metal contaminated soil remediation.