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

Some of plant growth-promoting rhizobacteria are endophytic bacteria that exist in the endo-rhizosphere and are able to promote plant growth via different mechanisms.

24 endophytic bacteria were isolated from the roots of grasses such as rice, wheat and barley using semi-solid nitrogen-free 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.

The dissolution of phosphate 1.67 times was higher in the presence of tri-calcium 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 Az-3 (2.28 mg/l) and Az-48 (0.75 mg/l), respectively; while the maximum dissolution of phosphate obtained with Az-52 (340.13 mg/l) and the least dissolution of phosphate occurred in Az-13 (98.13 mg/l). The highest K release was accomplished by Az-65 (6.66 mg/l) and the lowest was in Az-3 (4.78 mg/l). Finally, identification of robust isolates by 16S rDNA sequencing showed that Az-8, Az-19, and Az-50 are belonging to the Pseudomonas, Az-3 to Acinetobacter, Az-18 to Rhizobium, Az-48 to Enterobacter, and Az-63 to Advenella. Discussion and

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.