Insights into non-symbiotic plant growth promotion bacteria associated with nodules of Sphaerophysa salsula growing in northwestern China

  • Zhen-Shan DengEmail author
  • Zhao-Yu Kong
  • Bao-Cheng Zhang
  • Long-Fei Zhao
Original Paper


In addition to rhizobia, other non-symbiotic endophytic bacteria also have been simultaneously isolated from the same root nodules. The existence of non-symbiotic endophytic bacteria in leguminous root nodules is a universal phenomenon. The vast majority of studies have detected endophytic bacteria in other plant tissues. In contrast, little systemic observation has been made on the non-symbiotic endophytic bacteria within leguminous root nodules. The present investigation was carried out to isolate plant growth-promoting endophytic non-symbiotic bacteria from indigenous leguminous Sphaerophysa salsula and their influence on plant growth. A total of 65 endophytic root nodule-associated bacteria were isolated from indigenous legume S. salsula growing in the northwestern arid regions of China. When combining our previous work with the current study, sequence analysis of the nifH gene revealed that the strain belonging to non-nodulating Bacillus pumilus Qtx-10 had genes similar to those of Rhizobium leguminosarum Qtx-10-1. The results indicated that horizontal gene transfer could have occurred between rhizobia and non-symbiotic endophyties. Under pot culture conditions, out of the 20 representative endophytic isolates, 15 with plant growth-promoting traits, such as IAA production, ACC deaminase, phosphate solubilization, chitinase, siderophore, and fungal inhibition activity showed plant growth-promoting activity with respect to various plant parameters such as chlorophyll content, fresh weight of plant, shoot length, nodule number per plant and average nodule weight per plant when co-inoculated with rhizobial bioinoculant Mesorhizobium sp. Zw-19 under N-free culture conditions. Among them, Bacillus pumilus Qtx-10 and Streptomyces bottropensis Gt-10 were excellent plant growth-promoting bacteria, which enhanced the seeding fresh weight by 87.5% and the shoot length by 89.4%, respectively. The number of nodules grew more than 31.89% under field conditions. Our findings indicate the frequent presence of these non-symbiotic endophytic bacteria within root nodules, and that they help to improve nodulation and nitrogen fixation in legume plants through synergistic interactions with rhizobia.


Root nodules Plant growth promotion Phylogeny Non-symbiotic endophytes Sphaerophysa salsula 



This work was supported by the National Natural Science Foundation Project (31660106); Special Project of Service for Local Area Foundation of Education Department of Shaanxi Province of China (16JF029); Innovation Program of Shaanxi Province of China (2012CGX7; 2012KTZB03-02-03; 2016TTC-N-3-1); National Natural Science Foundation of China (U1204301) and Research Fund for County key technology project of Shanxi Province of China (2018XY-14); The Special Fund of Technology Innovation Team for the Development and Utilization of Biological Resources of Yan’an City; The Eighth Batch of Provincial Agricultural Standardization Demonstration Area Projects in Shaanxi Province in 2019.

Author contributions

Z-YK: formal analysis; B-CZ: methodology; L-FZ: software; Z-SD: supervision; Z-SD: visualization; Z-YK: writing—original draft

Compliance with ethical standards

Conflicts of interest

The authors declare no conflict of interest.

Research involving human participants and/or animals

This article does not contain any studies with human participants or animals performed by any of the authors.

Informed consent

Informed consent was obtained from all individual participants included in the study.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Zhen-Shan Deng
    • 1
    Email author
  • Zhao-Yu Kong
    • 2
  • Bao-Cheng Zhang
    • 3
  • Long-Fei Zhao
    • 4
  1. 1.College of Life SciencesYan’an UniversityYan’anChina
  2. 2.College of Life SciencesNanchang UniversityNanchangChina
  3. 3.School of Biological and Agricultural Science TechnologyZunyi Normal CollegeZunyiChina
  4. 4.College of Life SciencesShangqiu Normal UniversityShangqiuChina

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