We evaluated the growth promotion potential and colonization capacity of five endophytic bacterial strains for enhancing growth and yield of different maize cultivars under axenic and natural soil conditions. We found that the inoculant strains had the potential to improve maize seedling growth under axenic conditions. In the containment trial, FD17 inoculation significantly increased plant biomass and grain yield up to 39 and 42%, respectively, as compared to the un-inoculated control. We confirmed that strain FD17 is efficiently colonizes the rhizosphere, roots and stems of maize plant. Based on rigorous testing Enterobacter sp. FD17 showed highest potential to promote growth and health of maize grown under natural soil conditions. The second part of the study aimed to assess the drought stress resilience of maize and wheat through endophytic colonization by B. phytofirmans PsJN and Enterobacter sp. FD17 in the pot and field. Bacterial inoculation minimized the drought stress-imposed effects significantly increasing shoot biomass, root biomass, relative water content, photosynthesis and efficiency of PSII in the pot trial. The inoculant strains efficiently colonized maize seedlings and were recovered from roots, shoots and leaves of both irrigated and stressed plants. In the field, the plants were exposed to drought stress at tillering and flowering growth stage by skipping the respective irrigation. Inoculation increased grain yield up to 21 and 18%, respectively, at both stages over the control. These studies suggested that endophytic bacteria could be efficiently used to reduce the effects of drought stress on growth and yield of maize and wheat. In the third phase of study, we evaluated the L-TRP-dependent response of PsJN inoculation to maize growth and auxin biosynthesis under pot conditions. PsJN inoculation supplemented with L-TRP (10-5 M) significantly increased root and shoot biomass up to 62 and 55%, respectively, compared to control. The inoculant strain colonized more efficiently maize seedlings in the presence of exogenously applied L-TRP. The results imply that L-TRP-derived IAA biosynthesis in the rhizosphere by PsJN inoculation could be a useful approach for improving the growth and yield of maize.