Isolation And Identification Of Bacillus Megaterium TA-4 And Effects Of Its Bio-Organic Fertilizer On Tomato Growth And Soil Microbial Community

Bio-organic fertilizers have become more and more important in China's agricultural production due to their high fertilizer efficiency,low production cost,good effect and low environmental pollution.Bacillus spp.,favored for their unique biological characteristics and significant biocontrol potential,are predominant microbial flora in soil.TA-4 is a bacterium with indoleacetic acid(IAA)producing ability selected from the rhizosphere soil of tomato after fumigation in our laboratory.In this study,physiological and biochemical tests and molecular biological methods were combined to identify the species of this strain.Then the bio-organic fertilizer was prepared containing TA-4,and greenhouse tests were used to determine its effects on tomato biomass,defense enzyme activities,MDA,root vigor and chlorophyll content.The preliminary molecular mechanism of TA-4 bio-organic fertilizer inducing tomato resistance was revealed by determining the expression of relative protected genes,and its effects on soil microorganisms were also evaluated.The results of this research provide a theoretical basis for the application of this bio-organic fertilizer on tomatoes.The results of the study were summarized as follows:1.TA-4 was finally identified as Bacillus megaterium through the colony morphological observation,physiological and biochemical characteristics determination,as well as phylogenetic tree based on 16 S rRNA gene sequence analyses2.Greenhouse experiment results showed that B.megaterium TA-4 bio-organic fertilizer could significantly promote the growth of tomato plants.After using TA-4 bio-organic fertilizer at a concentration of 2% for 30 d,the growth-promoting effect of tomato was the best.Stem diameter,fresh weight and dry weight were increased by 58.69%,27.27%,53.24% and 70.64%,respectively,compared with the control group.After TA-4 bio-organic fertilizer treatment,the chlorophyll content,defense enzyme activities and root activity of tomato plants were significantly increased,and the MDA content was decreased,which effectively promoted the growth of tomato plants and improved the tomato's resistance to the adverse external environment.3.qRT-PCR results showed that after TA-4 bio-organic fertilizer treatment,the relative expression levels of SA-related genes PR-1a,JA-related genes LOX-D and ET response factor gene ERF2 in tomato plants significantly increased.The relative expression levels at 48 h after treatment were 3.62,4.81,and 7.27,respectively,indicating that B.megaterium TA-4 bio-organic fertilizer could induce resistance in tomato.4.The results of soil enzyme activities and plate counting showed that after TA-4 bio-organic fertilizer treatment,activities of urease,catalase,phosphatase,invertase and the number of culturable microorganisms in the rhizosphere soil were significantly higher than those in the control group.As the growth of tomato,the ratio of bacteria / fungus gradually increased,which indicated that B.megaterium TA-4 bio-organic fertilizer could promote tomato growth by changing the micro-ecological environment of the rhizosphere soil of tomato plants.