Isolation And Growth-promoting Characterstics Of Endophytic Bacteria From Cadmium Hyperaccumulator Tagetes Patula

In recent years,microbial-plant combined repair as a kind of enhanced phytoremediation technology has gradually become a hot research topic at home and abroad.As an important part of the plant micro-ecological system,plant endophytes can promote plant growth through a variety of ways,resist heavy metal toxicity,and improve plant enrichment of heavy metals.Endophytes have shown great potential in coordinating phytoremediation of heavy metal contaminated soils.In view of the increasingly serious soil pollution situation,selecting suitable repairing plants,screening functional endophytes,and studying the interaction mechanism between endophytes and plants are of great significance for promoting the practical application of microbial-plant combined repair technology.In this study,the cadmium super-accumulating plant Tageles patula was used as the material to separate and purify the endophytic bacteria by tissue separation method.The growth-promoting properties and heavy metal tolerance of the strain were studied.Combined with morphological characteristics,physiological and biochemical characteristics and 16S rDNA sequence,the molecular identification of the selected functional strains was analyzed.The effects of functional strains on germination of Tagetes patula and crop seeds under cadmium stress were studied by measuring the germination rate,root length and bud length.The aim was to lay a foundation for the utilization of functional strains.The following are the main findings.1.A sample of several Tagetes patula was collected,and the endophytic bacteria of Tagetes patula were isolated.28 endophytic bacteria were isolated from the root,stem and leaf tissues of Tagetes patula.2.The 28 isolated endophytic bacteria were subjected to qualitative and quantitative detection of growth-promoting properties,including auxin(IAA)production ability,iron carrier production ability,bacterial phosphorus solubilization ability and bacterial ACC deaminase activity.Twenty-one strains have IAA production ability.16 strains have iron carrier production ability,16 strains have phosphorus solubilization ability,and 9 strains have ACC deaminase activity.Among them.4 strains have four growth-promoting properties at the same time,and 4 strains have three growth-promoting properties at the same time.3.According to the results of the growth-promoting performance test,5 endophytic bacteria strains with better growth-promoting properties(KG1,KG3,KY7,KJ2,KJ6)were selected for Cd tolerance test.The results showed that 5 endophytic bacteria had good biological activity under the Cd stress of 100 mg/L.KG1 and KG3 could still grow well under the Cd stress of 1000 mg/L,indicating that these 5 endophytic bacteria have good cadmium tolerance.4.Based on endophytic bacterial growth promoting properties and cadmium tolerance,5 endophytic bacteria(KG1,KG3,KY7,KJ2,KJ6)were selected for testing the germination of Tagetes patula seeds with endophytic bacteria under different concentrations of cadmium stress(0-600 mg/L).The results showed that under low concentration of cadmium stress(0-200mg/L),the endophytic bacteria had no obvious promoting effect on the germination rate and germination potential of Tagetes patula seeds,and the promotion of bud length and root length was also weak.Under high concentration of cadmium stress(200-600 mg/L),five selected endophytic bacteria alleviated heavy metal toxicity and promoted the germination rate,germination potential,root length and bud length.The effect on the germination rate and germination potential was relatively higher,reaching 16.3%-44.5%,and the increase in root length and bud length is relatively smaller,only 6.0%-9.0%.5.Five endophytic bacteria(KG1,KG3,KY7,KJ2,KJ6)with good growth-promoting properties and cadmium tolerance were selected for testing the germination of wheat,rice and corn seeds with endophytic bacteria under different concentrations of cadmium stress(0-100 mg/L).The results showed that under low concentration of cadmium stress(0-20 mg/L),endophytic bacteria had weaker promotion effect on wheat seeds than non-soaked control group,and had no obvious promoting effect on rice seeds and corn seeds.Under high concentration of cadmium stress(20-100 mg/L),endophytic bacteria had significant effects on germination rate,germination potential,bud length and root length of wheat,rice and corn seeds,Among them,the promotion effect on rice was the strongest,reaching 11.1%-42.4%,and the promotion effects on wheat and corn reached 1.9%-36.8%and 1.4-21.5%,respectively.We successfully isolated and screened endophytic bacteria with plant growth-promoting properties and cadmium tolerance from Tagetes patula,and studied their effects on seed germination of Tagetes patula and other plants.It was found that five endophytic bacteria selected under a certain concentration of cadmium stress promoted the germination of Tagetes patula,wheat,rice and corn seeds,which provided a basis for further study on the application of endophytic bacteria in enhanced phytoremediation technology.