The Study On Isolation And Identification Of Growth Promoting Bacteria Producing ACC Deaminase And Inoculation Effects

In this study,the growth-promoting bacteria with ACC(1-aminocyclopropane-1carboxylic acid)deaminase activity were isolated from rhizosphere soils and roots of adult jujube plants in dry lands in northwestern China.The bacterial strains were identified by morphological characteristics,physiological and biochemical indexes and the homology analysis of 16S rDNA gene sequences.Then the strains with high ACC deaminase activity were inoculated back to 1-year-old Zizyphus jujuba grafts to study the strains against plants under drought stress.The effects of strain on plant growth and physiological characteristics under drought stress were studied,and the mechanism of increasing plant drought tolerance was discussed.The main results obtained were as follows:1.Using the medium with ACC as the only nitrogen source,the eighteen strains with high activity of deaminase were obtained from the rhizosphere and root of adult jujube plants in dryland of Northwest China.The ACC enzyme activity was between 4.13 and 2820?mol?-KA/(mgPr·h).At the same time,the growth characteristics of the obtained strains were determined by colorimetric method,liquid shaking culture method,and nitrogen-fixing medium.Finally,the results indicated that IAA concentration of the resulting strains produced is 0~41.51?g/mL,available phosphorus content is 3.13~534.86?g/mL,and the strains basically have the ability to fix nitrogen.2.According to colonymorphology,physiological and biochemical characteristics and16S rDNA molecular identification,strains were identified as Serratia plymuthica,Pseudomonas fluorescens,Pseudomonas koreensis,Pseudomonas brassicacearum,Pseudomonas putida,Pseudomonas lini,Pseudomonas taiwanensis,and Bacillus filamentosus.3.The strains of resistant strains G3?(Pseudomonas koreensis),G8?(Pseudomonas brassicacearum)and N5?(Bacillus filamentosus)were screened by natural resistance marker method to obtain three stable resistant mutant strains.Pot experiments were conducted to study the colonization of the three strains in the rhizosphere of jujube trees.The results showed that the number of the strains decreased after inoculation,and the G3?decreased most obviously.After 10 days of inoculation,the number of strains decreased to 7.10×10 3 cfu/g.After 20 days of inoculation,the number of strains tended to be stable.G8'decreased after inoculation,and the number of strains remained stable after 20 days of inoculation.The number of strains of N5?increased slightly at 30 days after inoculation and was 1.65×10 ~6cfu/g,and then stabilized.4.Under different water conditions,the inoculant can increase the net photosynthetic rate and chlorophyll content in different degrees.Plant proline content,soluble sugar content,SOD enzyme activity,POD enzyme activity,and root activity were significantly increased compared to the control.The relative electrical conductivity and malondialdehyde content of leaves inoculated with the inoculants showed different degrees of reduction,but had no significant effect on the water content of the plants.5.The above analysis shows that inoculation of the probiotics with ACC deaminase activity can increase the net photosynthetic rate,proline content,soluble sugar content,SOD enzyme activity,and POD enzyme activity,and reduce the relative electrical conductivity and malondialdehyde content,thus relieving plant drought stress.Among them,the microbial inoculum G8 has a significant effect on relieving plant drought stress.