The isolation and identification of endophytic actinobacteria from Glycyrrhiza glabra in the Tarim basin and their stress resistance and ability to promote plant growth

Endophytic actinobacteria isolated from roots, stems, and leaves of Glycyrrhiza glabra in the Tarim basin, Xinjiang were analyzed for diversity, stress resistance, and ability to promote plant growth activity. A total of 124 endophytic actinobacteria were isolated from 8 media. Based on traditional morphological observation, 32 representative strains were selected for 16S rRNA sequencing. According to the phylogenetic analysis, all of the strains belonged to Streptomyces sp. Subsequently, stress resistance and the ability to promote plant growth activity were evaluated. The results showed that the salt tolerance of strains decreased with increasing salt concentration, and 6.3% of the strains were able to tolerate 15% NaCl concentrations. All of the strains were able to grow on media of pH 7.0; however, only 3.1% could grow on media of pH 5.0 and pH 11.0, respectively. With a polyethylene glycol (PEG) concentration of 25%, the growth rate of strains decreased to 56.3%. When the PEG concentration reached 35%, strains were unable to grow normally. Moreover, 65.6% of the strains could produce indole-3-acetic acid, 50% of the strains had the ability to produce siderophores, and 25% of the strains were able to dissolve phosphorus. The results showed that Streptomyces sp. was the dominant genera of endophytic actinobacteria, and not only possessed strong resistance, but also had plant growth-promoting activity.