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UBC Theses and Dissertations

Impact of GFP-modification of Paenibacillus polymyxa on its ability to enhance growth of corn, canola and tomato seedlings Padda, Kiran Preet


Green fluorescent protein (GFP) as a marker gene has facilitated biological research in plant-microbe interactions. However, our knowledge about the effects of introduction of this marker protein in a microbe is very limited. I analyzed the effect of GFP-tagging of a plant growth-promoting bacterium, Paenibacillus polymyxa P2b-2R, on its ability to fix nitrogen and promote growth of important crop species: corn, canola and tomato. To evaluate this, corn, canola and tomato seeds were inoculated with P2b-2R and P2b-2Rgfp and grown for 40 days. Seedlings were harvested 20, 30 and 40 days after inoculation for evaluation of rhizospheric and endophytic colonization (cfu). Biological nitrogen fixation (¹⁵N dilution) and growth response (length and biomass) of P2b-2Rgfp inoculated seedlings was also compared with control and P2b-2R inoculated seedlings. The entire experiment was repeated to confirm the treatment effects. P2b-2Rgfp inoculated seedlings (i) accumulated upto 55% more biomass than non-inoculated controls and 17% more biomass than P2b-2R treated seedlings; (ii) were upto 41% longer than controls and 17% longer than P2b-2R treated seedlings; and (iii) fixed 18% of nitrogen from atmosphere (5% higher than P2b-2R). Canola seedlings inoculated with P2b-2Rgfp (i) had 118% more biomass than controls and 69% more biomass than P2b-2R treated seedlings; (ii) were 69% longer than controls and 37% longer than P2b-2R treated seedlings; and (iii) derived 22% of nitrogen from atmosphere (6% more than P2b-2R). But in case of tomato, P2b-2Rgfp and P2b-2R inoculated seedlings were analogous in terms of growth promotion and nitrogen fixation. Seedlings inoculated with either P2b-2Rgfp or P2b-2R were nearly 40% longer than controls, assimilated nearly 90% more biomass than controls, and fixed nearly 17% of nitrogen from atmosphere. P2b-2Rgfp and P2b-2R strains formed consistent rhizospheric and endophytic populations in corn, canola and tomato roots. To the best of my knowledge, these results represent the first evidence that transformation of a bacterial strain by GFP can significantly enhance its plant growth-promoting efficacy in corn and canola. Since the results of tomato were contrary to corn and canola, it can also be concluded that effect of GFP-tagging of P2b-2R might vary depending on the host plant.

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