Plant growth promoting rhizobacteria (PGPR) consist a wide range of beneficial soil bacteria, which inhabited in rhizosphere of plants and enhance the growth of plant via production and secretion of various regulatory molecules in the vicinity of rhizosphere. In the present study, twenty two plant growth promoting rhizobacteria were isolated from 5 samples of rhizosphere of tomato cultures (Mehdia, Tunisia). The isolates were screened for the plant growth promoting capability after the treatment of tomato seeds with the selected rhizobacteria strains. The treatment of the plants with the selected plant growth promoting rhizobacteria MS3, showed higher plant growth in comparison with the control, accompanied by the increasing root length 191%, fresh weight 224%, leafs number 233% and shoot length 80% after 24 days of sowing. Furthermore, an excellent effect of Microbacterium arthrosphaerae on tomato culture growth in seed germination and seedling early establishment under aerobic cultivation system has been observed. The identification of the isolated, selected rhizobacteria strains MS3 by the using of 16S rRNA gene sequence analysis indicated their belonging to the genus Microbacterium arthrosphaerae and the investigation manifested an important potential of plant growth promotion with a capability to produce indole-3-acetic acid (36 μg/ml), in the presence of tryptophan in the culture medium and salicylic acid (132 μM/l), which was responsible for nitrogen fixation and inorganic phosphates solubilization. The present study revealed an excellent effect of PGPR Microbacterium arthrosphaerae on the improvement of tomato culture growth
