Study On The Promoting Mechanism Of Two Strains Of Bacillus Spp.

Plant rhizosphere-promoting bacteria can directly promote plant growth by dissolving phosphorus,fixing nitrogen,decomposing potassium,producing indoleacetic acid,and the like,and also enhancing the plant’s resistance to stress by secreting siderophore and ACC deaminase.In this study,two strains of HP9 and HP10 isolated from tea rhizosphere were identified,and the growth-promoting properties were analyzed by measuring the ability of phosphorus solubilization,ACC deaminase secreting and siderophore production.The effects of plant growth,microbial diversity and soil fertility on peanut rhizosphere were studied after inoculated with two strains and mixed strains by pot experiment.And colonizing abilities of two strains in peanut rhizosphere soil and plants were investigated by rifampicin labeling technique.The growth promoting mechanism of two strains on peanuts were explored and analyzed.The research results are as follows:According to its morphological characteristics,physiological and biochemical tests and molecular biological identification,HP9 strain was identified as Bacillus velezensis,and HP10 strain was Bacillus firmus.Studies on growth-promoting properties showed that both HP9 and HP10 strains could dissolve phosphorus,and the best phosphorus-solubilizing ability was obtained when glucose was used as carbon source,potassium nitrate and ammonium sulfate were respectively nitrogen sources.Metabolomics analysis showed that HP9 strain significantly increased the contents of lactic acid,maleic acid and oxalic acid,and newly synthesizing organic acids such as glucose heptanoic acid and sulfuric acid;while HP10 increased the content of5-aminovaleric acid in the culture supernatent,and newly synthesizing organic acids such as ascorbic acid.The two strains decreased p H value of the culture to play role in phosphorus solubilization by secreting different types of organic acids.In addition,both strains could produce siderophore,and HP9 strains also secrete ACC deaminase.The pot experiment showed that HP9,HP10 and complex flora of HP9 and HP10 promoted the growth of plant length,plant height and fresh weight of peanuts,andsignificantly increased the content of alkali nitrogen in the rhizosphere soil of peanuts.And the available phosphorus and potassium content have also increased.The results of bacterial and fungal diversity analysis on peanut rhizosphere soil showed that the relative abundances of Bacteroides,Proteobacteria and Mortierellomycota were significantly increased;whereas of Verrucomicrobia,Acidobacteriathe and Olpidiomycota were significantly reduced compare to control.From a genera level,the relative abundance of Chryseobacterium and Arthrobotrys was significantly increased,and the relative abundance of Bradyrhizobium and Sebacina was significantly reduced.Rifampicin-labeled strains were all detected in the rhizosphere soil and plant roots,stems and leaves after inoculated with rifampicin-resistant strains.In conclusion,both Bacillus sp.strains HP9 and HP10 have the ability to dissolve phosphorus and secreting siderophore.After inoculated with these strains on peanuts,the rhizosphere soil ferilities were improved by the direct growth-promoting properties of the strains;and peanut plants were promoted and the activities of rhizosphere soil microbes were affected by colonization in the rhizosphere soil and peanut tissues.These research comprehensively analyzed the growth promoting mechanism of two strains of Bacillus spp.on peanuts,and the research results laid the foundation for the further development of microbial agents.