Seedling growth promotion and nitrogen fixation by a bacterial endophyte Paenibacillus polymyxa P2b-2R and its GFP derivative in corn in a long-term trial

A plant growth promoting endophyte, Paenibacillus polymyxa P2b-2R, originally isolated form a lodgepole pine seedling and its green fluorescent protein (GFP) derivative, P2b-2Rgfp, were evaluated for their ability to survive, fix atmospheric nitrogen (N) and promote plant growth when inoculated into corn (Zea Mays L.) in a long-term trial. We were also interested to see the effects of GFP-tagging of P2b-2R on its ability to promote growth of corn seedlings in a long-term study. Corn seedlings were inoculated with either strain P2b-2R or P2b-2Rgfp and non-inoculated seedlings were treated as controls. Seedlings were harvested after 3 months and evaluated for plant growth promotion (length and biomass) and N fixation (N-15 foliar dilution assay). Colonization and survival of P2b-2R and P2b-2Rgfp outside (rhizosphere) and inside (internal tissues) the inoculated seedlings were also determined. Both strains survived inside and outside corn seedlings forming rhizospheric and endophytic colonies in stem and root tissues. Inoculation by P2b-2R strain promoted corn plant growth via enhancing seedling length and biomass by 52 % and 53 %, respectively. Similarly, P2b-2Rgfp inoculation enhanced seedling length by 68 % and biomass by 67 %. Corn seedlings inoculated with strain P2b-2R derived 30 % of foliar N from the atmosphere and seedlings inoculated with P2b-2Rgfp derived 32 % of foliar N from the atmosphere. But there was no statistically significant difference between P2b-2R and P2b-2Rgfp treated seedlings in terms of overall seedling length, biomass and amount of N fixed in this long-term trial. These results combined with the results from an earlier study suggest that P. polymyxa P2b-2R and its GFP-tagged derivative is capable of enhancing overall plant growth throughout the life cycle of corn plant.