Study Of Screening And Plant-growth Promoting Function Of Endophytic Bacteria From Hippophae Rhamnoides Root Nodules

Hippophae rhamnoides root nodules are formed by Frankia infecting its root.There are a large number of endophytic bacteria in the root nodules of Hippophae rhamnoides except Frankia.Endophytic bacteria have a variety of biological functions such as promoting plant growth.Endophytic bacteria can promote plant growth because some strains can produce indole-3-acetic acid?IAA?,siderphore and dissolve insoluble phosphate and so on.The study explored the plant-growth promoting potential of endophytic bacteria from Hippophae rhamnoides root nodules,which can provide the theoretical basis for the development of microbial fertilizers.131 strains of endophytic bacteria from Hippophae rhamnoides root nodules were used as materials for this study.The strain SR308,which can produce plant-growth promoting substances,was screened from 131 endophytic bacteria of Hippophae rhamnoidesrootnodulesthroughtheSalkowskicolorimetricmethod,Mo-Santispetrophotography method and Chrome Azurol S?CAS?plate assay method.In addition,strain SR308 was identified by morphological,physiological and biochemical tests and 16S rRNA gene sequence analysis.The growth conditions of strain SR308 were optimized by single factor experiments and response surface methodology.The effects of strain SR308 on seed germination were tested through filter paper culture experiment.At the same time,the pot experiments of cucumber growth at different growth stages were studied by using the fermentation broth of strain SR308.It mainly has obtained the following results:1.The endophytic bacteria of plant-growth promoting activity from Hippophae rhamnoides root nodules were screened and identified.Among 131 strains,13 strains have the ability to produce IAA,8 strains have the ability to dissolve insoluble phosphorus,and 5 strains have the ability to produce siderphore.Strain SR308displayed high growth promoting activity,which has produced IAA and siderphore(23.17±0.17?g·mL^-1,4.90±0.37%),and has solubilized phosphate(1.36±0.006?g·mL^-1).Strain SR308 was identified as Bacillus mycoides.2.The growth conditions of the strain SR308 from Hippophae rhamnoides root nodules were optimized.The results of single factor tests showed that the most suitable growth conditions of SR308 were determined as following factors:culture temperature30?,incubation time 36 h,pH value 7.0,rotation speed 180 r·min^-1,medium volume75 mL/250 mL,the seed growth time 16 h.The results of response surface methodology showed that most suitable medium for the growth of the strain SR308 was determined as following factors:maltose 8.5 g·L^-1,peptone 16.6 g·L^-1,beef extract 3.3 g·L^-1,KCl5.6 g·L^-1.Under these conditions,the maximum number of viable bacteria reached4.4×10⁸CFU·mL^-1,which was 3.7 times higher than that before optimization.3.The effects of the strain SR308 on seed germination of different plants were studied.The seed germination experiments showed that SR308 fermentation broth promoted the germination of both wild and artificial cultivation Hippophae rhamnoides seeds when the optimal soaking time was 24 h and the optimal soaking with concentration were 4.4×10⁶ CFU·mL^-11 and 4.4×10⁷ CFU·mL^-11 respectively.The strain SR308 fermentation broth promoted the germination of cucumber,cabbage,corn and cherry tomatoes seeds,while it inhibited the germination of pea,lycium barbarum,strawberry and mentha haplocalyx seeds.The strain SR308 fermentation broth promoted the germination of both rape and cayenne seeds when concentration were4.4×10⁶ CFU·mL^-1,while it inhibited the germination when concentration were 4.4×10⁷CFU·mL^-1.4.Pot experiments of the strain SR308 on cucumber growth at different growth stages were studied.Different concentrations of strain SR308 fermentation broth inhibited root and stem growth of cucumber at radicle stage,but it significantly promoted the growth of cucumber at seedling and adult stages.When the concentration of SR308 fermentation broth was 4.4×10⁸ CFU·mL^-1,it significantly has promoted the growth of cucumber above-ground parts,enhanced chlorophyll content and SOD activity,decreased MDA content and POD activity in cucumber leaves at seedling and adult stages.