Screening Of Cadmium-resistant Endophytic Bacteria In Tagetes Patula And Study On Its Interaction With Cadmium

Endophytic bacteria are an important part of plant micro-ecosystem and have a close symbiotic association with host plants.Their excellent properties in heavy metal absorption and tolerance,show great potential for the remediation of heavy metal pollution.Research on the interaction between endophytic bacteria and heavy metals is of great significance to promote the large-scale application of endophytic bacteria to heavy metal pollution remediation.Tagetes patula is a Cd hyperaccumulator,and its endophytic diversity and its interaction with metals have not been fully studied.In this study,phylogenetic trees were constructed using endophytic bacteria isolated from as materials.The diversity of endophytic bacteria in Tagetes patula and its ability to toterate heavy metals was tested.Characteristics of activation and adsorption of cadmium under different environmental conditions were analyzed.The following are the main findings.1.16Sr DNA sequence analysis showed that the endophytic bacteria isolated from the Tagetes patula belong to 10 genera,namely Proteus,Alcaligenes,Klebsiella,Pseudomonas,Providencia,Lysinibacillus,Brevundimonas,Achromobacter,Bacillus,Myroides,Proteus and Pseudomonas are the dominant genus of endophytic bacteria of comfrey,accounting for 21%and 18%of the total,respectively.Among different tissue parts,the endophytic bacteria in the roots had the highest separation rate,and the endophytic bacteria in the leaves had the highest diversity.2.Endophytic bacteria isolated from different tissues of plants have very different tolerances to Cd.Among the strains isolated from the roots of the plants,the strains KG1,KG9,and KG 10 showed strong cadmium tolerance.Only one strain isolated from the leaves maintained good biological activity under the stress of Cd2+1000mg/L.Among them,strains KY2 and KY3 had strong cadmium tolerance.The cadmium tolerance of the strains isolated from the stems was poor.The endophytic bacteria isolated from the roots showed better performance in both quantity and cadmium tolerance than the stem and leaf endophytic bacteria.3.The growth curve trends of the strains were roughly the same,including lag phase,log phase,and stable phase.The effect of temperature on the growth of strains is different,and the ability to withstand temperature changes is:KG10>KG7>KG9>KY8.The optimal temperatures of the strains KG7,KG9,KG 10 and KY8 were around 18℃,30℃,30℃ and 3℃,respectively.At the optimal temperatures,the acid production capacity of the four strains was also strong.The four strains have a wide range of adaptation to pH,and the strains KG7 and KY8 are more resistant to different pH.The optimum pH of the strains KG7,KG9,KG 10 and KY8 were around 7.2,7.2,8,and 6.4.Endophytic bacteria have the ability to activate solid cadmium in the culture broth.As the pH decreased,the content of water-soluble cadmium increased to varying degrees.The ability of the strain to activate solid cadmium in the culture broth is KY8>KG10>KG7>KG9,which is roughly the same as the acid production test results of the strain,which indicates that the activation capacity of the strain may be mainly related to the acid production of the strain.Endophytic bacteria have the ability to activate cadmium in the soil.After inoculation,the content of water-soluble cadmium increases,and to a certain extent,it promotes the dissolution of Cd2+ in the soil.The ability to activate cadmium in soil is related to the degree of soil pollution.In 50mg/kg cadmium-contaminated soil,the ability to activate is shown,but it is poor in 100mg/kg cadmium-contaminated soil.KY8 can be used for further activation experiments.5.Endophytic bacteria have a certain adsorption capacity for cadmium ions,and the time for the strains to reach adsorption equilibrium is shorter.Strains KG7 and KG10 have strong adsorption capacity,while strains KG9 and KY8 have weak adsorption capacity.In addition,the entire adsorption process may involve the combined action of extracellular and intracellular adsorption.KG 10 can be used for further adsorption experiments.