Effect of GFP-tagging on nitrogen fixation and plant growth promotion of an endophytic diazotrophic strain of Paenibacillus polymyxa

摘要

Green fluorescent protein (GFP), a renowned marker protein, is typically believed to be inert with respect to affecting the physiology of the bacteria it occurs in. We analyzed the effects of GFP-tagging on the ability of an endophytic diazotroph, Paenibacillus polymyxa P2b-2R, to fix nitrogen and promote the overall growth of corn plants. The growth response and the amount of nitrogen fixed by P2b-2Rgfp-inoculated plants were compared with uninoculated controls and P2b-2R-inoculated plants at three harvests. P2b-2Rgfp inoculation significantly increased the biomass of corn plants as compared with non-inoculated controls and P2b-2R-treated plants. In-vitro tests revealed that strains P2b-2R and P2b-2Rgfp possess various plant-growth-promoting characteristics, namely phosphate solubilization, production of siderophores, indole acetic acid, ammonia, and enzymes such as cellulase, protease, and catalase. P2b-2Rgfp-inoculated plants fixed 18% atmospheric nitrogen, which was significantly higher than the P2b-2R-inoculated plants (15%). This difference led us to compare the expression of structural nif genes ( nifH, nifD, nifK) of strains P2b-2R and P2b-2Rgfp. We observed that expression levels of structural nif genes of strain P2b-2Rgfp were 1.5-fold higher than those of strain P2b-2R. These results indicate that GFP-tagging positively affects the efficacy of strain P2b-2R with respect to promoting plant growth and fixing nitrogen, perhaps by increasing the expression levels of structural nif genes.