Screening And Identification Of Growth-promoting Rhizobacteria From Sabina Vulgaris

Plant growth-promoting rhizobacteria are beneficial rhizosphere bacteria that live in the microdomain of plant rhizosphere and antagonize pathogenic bacteria or promote plant growth.Although a large number of rhizosphere growth-promoting bacteria have been isolated in recent years.These bacteria have one or more characteristics of secreting hormones,fixing nitrogen,dissolving phosphorus and improving host system resistance,but these bacteria are not very resistant and have growth-promoting function under suitable cultivation conditions,but they can survive in unhealthy growth environment.Live,but lose growth-promoting properties,such as no longer secreting hormones.Therefore,it is urgent to screen PGPR bacteria with good stress resistance and growth promoting effect.Sabina vulgaris is a unique plant with strong stress resistance in Yulin area.It is salt-alkali,drought-tolerant,drought-tolerant,disease-resistant and insect-resistant.However,the study of screening rhizosphere growth-promoting bacteria for Sabina vulgaris has not been reported.In this study,a plant endophytic bacteria was isolated from the root of Sabina vulgaris,which is endemic to northern Shaanxi Province and has strong resistance to stress.The bacteria was named SDB9 in the laboratory.?1?The bacteria were spherical bacteria and colony cultured for a long time showed rosy color.The results of Gram staining showed that SDB9 was positive and Gram-positive bacteria?G+?.The results of environmental scanning electron microscopy showed that the strain had a thick capsule.The diameter of the strain was about 784.8-890.6 nm from the high resolution scanning electron microscopy photos.According to 16S rDNA sequence analysis of Endophytic bacteria,SDB9 belongs to the genus Kocuria,SDB9 bacteria have strong salt and alkali tolerance.?2?Na₂CO₃ simulated salt-alkali stress experiment showed that SDB9 bacteria could improve the salt-alkali tolerance of mung bean seedlings,have a certain green-keeping function,and make new leaves grow faster,roots more developed,lateral roots more,especially compound petioles significantly longer.The indoor pot experiment showed that the chlorophyll of mung bean treated with bacteria increased by 7.81%.The SOD activity of mung bean treated with bacteria had no significant difference from that of control group,and the POD content had no significant change.However,the CAT activity of mung bean in the treatment group increased by 5 times and the difference was very significant;the MDA content of mung bean inoculated with bacteria decreased by 5.34%,the difference was not significant;the proline content of mung bean inoculated with endophytic bacteria was significantly higher than that of the control group,which increased by 41.24%,the difference was very significant.Similar results were obtained from indoor pot experiments on monocotyledon Gramineae maize.?3?The results of hormone determination by mass spectrometry showed that the IAA content of SDB9 was very high,the content was 7748.1 ng/g,and the cytokinin content was high,mainly isoprenyl adenosine?iPR?and isoprenyl adenine?iP?,the contents were28.9 and 1.41 ng/g,respectively,while the content of trans-zeatin cytokinin was very low.?4?One chromosome and three plasmids were obtained from the genome of SDB9 strain of Sabina vulgaris.The three plasmids were named A,B and C respectively.In-depth bioinformatics analysis showed that there were two amidase genes in SDB9 genome.These genes belonged to IAM pathway of IAA synthesis,four aldehyde dehydrogenase genes,and these genes belonged to IPyA/TAM/TSO pathway of IAA synthesis.Aldehyde dehydrogenase gene ALDH4 is special,The highest homology with NCBI database is Arthrobacter sp.U41,with 80.39%homology,while the homology with Kocuria is low.?5?Preliminary field experiments showed that SDB9 has the function of dissolving potassium,which can improve the content of available potassium in corn rhizosphere soil,and promote the absorption of nitrogen;it can make the ear of rice grow longer,the number of spikelets increase,and then the number of grains increase significantly,and finally improve the yield by about 10%.In conclusion,we isolated a salt-and alkali-tolerant PGPR strain SDB9 from the rhizosphere of Sabina vulgaris,which can stimulate plant growth and improve host resistance at least by secreting hormones such as IAA and dissolving potassium.We also found the genes involved in IAA synthesis in SDB9 genome,and exists a Aldehyde dehydrogenase gene ALDH4 which had low sequence homology with other Kocuria rosea strains.