Isolation of endophytic bacteria from Rehmannia glutinosa Libosch and their potential to promote plant growth

In order to study the growth promoting potential of endophytic bacteria from Rehmannia glutinosa Libosch, a total of 25 different bacteria belonging to 7 genera were identified by 16S rRNA gene sequencing, including Bacillus, Micrococcus, Lysinibacillus, Brevibacterium, Halomonas, Kocuria and Terribacillus. In this study, thirteen bacterial strains were found to solubilize inorganic phosphate, with the isolate Kocuria rosea (EH15) having the highest phosphorus dissolution activity (3.70 μg/mL). Twelve isolates were positive for nitrogen fixation abilities. Twenty-two strains produced indole-3-acetic acid (IAA) in the presence of L-tryptophan, and eleven of the twenty-two isolates synthesized IAA in the absence of L-tryptophan. The strain K. rosea (EH15) was capable of producing the highest IAA amount (15.36 and 7.98 mg/L) in Luria Bertani (LB) broth containing 0.2% L-tryptophan and lacking L-tryptophan, respectively. Ten isolates had siderophore production abilities with Bacillus amyloliquefacieus EH10 (0.26) and Brevibacterium frigoritolerans EH13 (0.32) showing high siderophore production characteristics. Five bacteria endogenous were selected to evaluate the growth parameters of Brassica napus L. and all isolates exhibited a significantly greater increase in seedling height, root length, fresh weight and dry weight, than the control plants. The greatest improvement appeared in the case of co-inoculation of EH10 and EH15, except in dry weight, and the biggest enhancement in dry weight occurred in the strain EH15. In general, these endophytic bacteria indicate a potential as microbial fertilizers to promote the growth of R. glutinosa Libosch.