Isolation Of Rhizobacterium With Plant Growth-promoting Rhizobacteria Functions

In this paper, using the method of enriching aim bacterial stains, forty-six strains of plant growth-promoting rhizobacteria(PGPR) were isolated from rhizosphere of vegetables ,based upon the ability to utilize the compound 1-aminocyclopropane-1-carboxylate (ACC) as a sole nitrogen source. Then, the stain named XG35 antagonistic against Phytophthora capsici was further selected from these ACC deaminase-containing rhizobacteria. And it was considered to be a bifunctional PGPR. Our work involved with studying on its activities of plant-growth promoting and colonization on tomato under different conditions, preliminarily probing conditions for ACC deaminase production and effects of factors on ACC deaminase activity and researching into its PGPR functions and inhibiting mechanism to capsicum. And then, identificating of the strain according to physiological and biochemical property,Biolog and 16SrDNA analysis.Three strains XG35, LA1, YC1,had higher levels of ACC deaminase activities and facilitated the seedlings growth of tomato. Adding bacterial suspensions to petri dishes resulted in higher plant growth-promoting activity than seed inoculation. Moreover, these three stains could confer resistance in tomato seedlings under 0.5% NaCl stess and alternate 5℃low tempreture stress. The stains XG35,LA1 had activities of colonization on tomato roots(>105cfu),and the stain XG35 had higher one. The optimal conditions for ACC deaminase production were as follows: initial pH of inducting medium 7.5;temperature of induction, 25～30℃; time of induction, 24～42h; concentration of ACC, 3.0mM. ACC deaminase from the stain XG35 had a temperature optimum at approximately 30℃and a pH optimum of 8.0; When the enzyme was heated at temperatures of 5～65℃for 30min,it had better stability within 35℃,but there was no activity at 65℃.And when it was heated in different buffers of pH5～11for 6h,it had better stability at pH7.5～9.5,which showed that ACC deaminase had higher stability in alkaline buffer.Moreover, Cu2+and Zn2+ ions could activate ACC deaminase, while Hg2+and Ag+ could inhibit the enzyme activity.The stain XG35 also had high activity of colonization on capsicum roots and the root colonization density reached 2.6×106cfu/g soil after 35 d. It facilitated the plants growth of capsicum significantly.Compared to CK, the plants had strong stems, bigger and greener leaves and strong roots. The stain XG35 could efficiently inhibit the mycelium growth of P. capsici and was an efficient biological control agent to control Pepper Phytophthora blight.Root drenching with XG35 cultures gave 72.8% and 60.5% control efficacies respectively, on capsicum seedlings 7 d and 14 d after inoculation of the pathogen P. capsici,while spraying on fruits gave 72.4% control efficacy to the fruit Phytophthora blight 4 d after inoculating the pathogen. Moreover, the control efficacy of inoculating the pathogen upwards 24h after spraying XG35 cultures on fruits was better than inoculating the two synchronously. The screening study demonstrated XG35 had a plate ability of cellulose and weak ability ofβ-1,3-glucanase.According to plate cultural characteristic,morphological characteristic, physiological and biochemical property,Biolog and 16SrDNA analysis, the strain XG35 was identified to be Pseudomonas fluorescens biovarⅣ.