Isolation of Endophytic Bacteria from Grasses Root and Assessing Phosphate Solubilization, Potassium Releasing and Auxin Production Abilities of Isolated Bacteria

Introduction: Some of plant growthpromoting rhizobacteria are endophytic bacteria that exist in the endorhizosphere and are able to promote plant growth via different mechanisms. Materials and methods: 24 endophytic bacteria were isolated from the roots of grasses such as rice, wheat and barley using semisolid nitrogenfree bromothymol blue (NFB) medium. PGP features including phosphate solubilization, indole acetic acid (IAA) production, potassium releasing and siderophore production were measured according to the standard methods. Results: The dissolution of phosphate 1.67 times was higher in the presence of tricalcium phosphate (TCP) than rock phosphate (RP), and K release from biotite was more than muscovite (4.7 times); furthermore more IAA was produced in the presence of tryptophan, and this increment was by 30%. The highest and lowest amount of IAA were recorded in Az3 (2.28 mg/l) and Az48 (0.75 mg/l), respectively; while the maximum dissolution of phosphate obtained with Az52 (340.13 mg/l) and the least dissolution of phosphate occurred in Az13 (98.13 mg/l). The highest K release was accomplished by Az65 (6.66 mg/l) and the lowest was in Az3 (4.78 mg/l). Finally, identification of robust isolates by 16S rDNA sequencing showed that Az8, Az19, and Az50 are belonging to the Pseudomonas, Az3 to Acinetobacter, Az18 to Rhizobium, Az48 to Enterobacter, and Az63 to Advenella. Discussion and conclusion: Our results revealed that different genera of bacteria with varied PGP traits are existing as endophytic bacteria in the plant roots. In total, these bacteria were able to solubilize more phosphate from TCP than RP; and higher K from biotite than muscovite. It seems that the production of organic acids is the main mechanism of P and K solubilization. Moreover, higher production of IAA was measured in the presence of tryptophan. Further research, especially in pot or farm, is necessary to assess the effects of these bacteria.