Endophytic bacteria from Pueraria montana var. lobata in Guangxi: isolation, identification, and characterization of plant growth-promoting effect

Abstract:

[Background] Endophytic bacteria coexist with the host for a long time, posing an impact on the growth and development of the host. Pueraria montana is an important plant with both medicinal and edible values. The research on the endophytic bacteria of this plant is of practical significance. [Objective] To isolate and identify the endophytic bacteria from the roots of Pueraria. montana var. lobata growing in Guangxi and analyze their growth-promoting effect, so as to learn the community structure and growth-promoting effects of endophytic bacteria from the medicinal and edible plants, and provide references for revealing the role of endophytic bacteria in the production and quality formation of medicinal and edible plants and the development and utilization of endophytic bacterial resources. [Methods] Six different media were used to isolate the endophytic bacterial strains from the root nodules, root system, and root callus of Pueraria montana var. lobata. The 16S rRNA gene sequencing was employed to explore the distribution characteristics and genetic diversity of the endophytic bacteria. The physiological and biochemical tests were carried out to determine the nitrogen-fixing activity, phosphorous-solubilizing properties, siderophore production, and indole acetic acid (IAA) secretion of the isolated strains. [Results] A total of 223 strains were isolated from the root nodules, root system, and root callus of Pueraria montana var. lobata. These isolates were phylogenetically classified into 19 genera, 10 families, 4 classes of 2 phyla based on their 16S rRNA gene sequences. Bacillus, Pseudomonas, Agrobacterium, Enterobacter were the predominant taxa. The number and community structure of the endophytic bacteria varied between tissues. Specifically, the number of the endophytic bacteria was in the order of root nodules>root system>root callus and the diversity in the order of root callus>root system>root nodules. Furthermore, the bacterial communities were also distinct from various culture media showed different richness. There were 6 strains with nifH gene, 15 strains with four growth-promoting properties including nitrogen fixation, phosphorous solubilizing, siderophore production, and IAA secretion, and 17 strains with three growth-promoting properties were selected from the tested strains. [Conclusion] The endophytic bacteria in the roots of Pueraria montana var. lobata from Guangxi are genetically diverse, with the distribution varying between tissues and multiple growth-promoting properties.