Plant Growth Promoting Rhizobacteria Cultivation Optimization And Mechanism Research

SZ7-1 isolated from mangrove in Southern China was studied in this paper, which including capacity of phosphate solubilization and nitrogen fixation. Firstly, we optimized the culture condition of SZ7-1. Then the SZ7-1* containing the green florescence protein (GFP) was selected to inoculant experiment. Strains were inoculated in eucalypts seedlings and colonization condition of SZ7-1*on the colonization roots were observed by FM and SEM. The bacteria numbers were detected by plate counts after harvest for inquiring survival rate of SZ7-1*.The biomass and N uptake were estimated to access the effect of the colonization process of SZ7-1* on eucalypt seedlings growth. The results were as follows:A plant growth-promoting rhizobacteria (PGPR) strain, SZ7-1, was obtained from mangrove rhizosphere and tested previously for potential applications. To develop an economical and practical fermentation medium for the growth of SZ7-1, response surface method was used in this study. Plackett–Burman factorial design was used to examine the significance of 11 different media on the growth of SZ7-1. Experimental result demonstrated that media consisting of corn syrup, yeast extract and K₂HPO₄ significantly improved the growth process. The effect of different combinations of the three nutrients on the growth of SZ7-1 were further explored in a Box-Behnken design. The optimal concentration of each nutrient for maximum growth were corn syrup 28 g/L, yeast extract14 g/L and K₂HPO₄ 2.2 g/L. The optimized medium enhanced the growth of SZ7-1 by 12.4, 2.4 and 5.5 times more than the original medium, LB and cow meat extract protein peptone medium, respectively.With the plant growth promoting bacteria SZ7-1 as the object of study, the culture condition of SZ7-1 was optimized by using singe-factor design and the response surface methodology(RSM),and the optimal culture conditions were used in the 5L auto fermentor. In this paper,the optimum culture condictions for SZ7-1 growth were firstly determined through singe-factor analysis. The results showed as follows: initial pH4.5-7.5, volume of medium in flask 10%-30%,inoculum size1%-5%.The response surface methodology was applied to study the interactions and optimization of the culture parameters for SZ7-1 which were explored by experiments.The experimental results showed that the optimum conditions for germination as follows:pH6.02, inoculum size2.41%and volume of medium in flask 10%. With two different culture conditions ,The growth of SZ7-1 was analyzed in the 5L auto fermentor. The results indicated that the optimized culture conditions were testified to be more suitable for the growth of SZ7-1 strains,and live bacterias reached 1.31×10¹⁰ cfu/mL,which wass 1.62 times more than before the optimization. Correlation analysis showed that: Logarithm of bacterial counts (lg), OD values, and pH value were extremely significant correlation with each other.The eucalyptus seedling roots were inoculated with SZ7-1*(containing GFP) for 12 weeks. The results of observation by FM and SEM and bacteria counts showed that SZ7-1* colonized roots surface as well as soil and ever inner cortex of eucalyptus seedling. An overall increase in plant growth was observed with inoculation of these bacteria, which was found to increase plant dry matter and nitrogen uptake. This research indicated that the SZ7-1* strain had a beneficial ability of growth-promotion on eucalyptus seedling under greenhouse conditions.