Screening of growth-promoting rhizobacteria from Spartina alterniflora and identification of their volatile organic compounds

【Objective】The strains with the ability to release volatile organic compounds（VOCs）to promote plant growth were screened from the rhizosphere bacteria of Spartina alterniflora，and the components of VOCs released were analyzed and identified to provide strain resources and theoretical basis for promoting plant growth.【Method】A total of 85 strains of bacteria were isolated from the rhizosphere soil of S. alterniflora as tested bacteria，and the VOCs growthpromoting strains were screened by co-culture with Arabidopsis thaliana in a two-partition culture dish. To further evaluate the multiple growth-promoting functions，the entropy method was used to select the best strain. It was classified by morphology，physiological and biochemical features，16S rRNA and gyrB gene analysis. Finally，the VOCs components of the strain were identified by solid-phase microextraction and gas chromatography-mass spectrometry（GC-MS）.【Result】Six bacteria that could promote the growth of A. thaliana by releasing VOCs were screened：GXMZU2281GXMZU2346，GXMZU2401，GXMZU3251，GXMZU3294，GXMZU4388. Among them，GXMZU4388 strain had the ability of solubilizing phosphorus，nitrogen fixation，siderophore and heteroauxin（IAA）production. Compared with the control group，GXMZU4388 strain could greatly promote the growth of tomato under the treatment of 20 times and 100 times diluted bacterial solution，and the fresh weight increased by 144.0% and 186.2% respectively. The comprehensive evaluation scores of entropy method were the highest in GXMZU4388 strain. GC-MS was used to identify that the strain could produce 9 VOCs components，of which 8 components have been reported to have the function of inhibiting bacteria or promoting plant growth. The relative contents of 6-methyl-2-heptanone，5-methyl-2-hexanone，5-methyl-2-heptanone and 3-methyl-2-pentanone were relatively high，which occupied a dominant position. Combined with morphological observation，physiological and biochemical characteristics analysis and molecular biological identification of 16S rRNA and gyrB gene sequences，GXMZU4388 strain was identified as Bacillus safensis.【Conclusion】GXMZU4388 had excellent performance in promoting plant growth in all aspects. It can also significantly exert its ability to promote plant growth at low concentrations，and can release a variety of VOCs that are beneficial to plant growth and bacteriostasis. It has excellent application potential in the development of bacterial fertilizer.