Isolation and identification of Halomonas sp. Bachu 26 with plant growth-promoting effect from rhizosphere of Tamarix chinensis under salt stress

Abstract:

Salinization is a global soil problem. Plant growth-promoting rhizobacteria (PGPR) have unique advantages in remediating saline-alkali soils and promoting plant growth. Screening the rhizosphere microorganisms of Tamarix chinensis, a typical halophyte, and revealing the growth-promoting effect and mechanism of these microorganisms are of great significance for developing microbial fertilizers. [Objective] To screen out the microorganisms from the rhizosphere soil of saline-alkaline tolerant T. chinensis and measure their basic characteristics, salt and alkali tolerance, and plant growth-promoting effects. [Methods] A saline-alkali tolerant strain Bachu 26 was screened out from the rhizosphere soil of wild T. chinensis in Bachu, Xinjiang and identified based on the morphological, physiological, and biochemical characteristics and 16S rRNA gene sequence. We cultured the strain Bachu 26 in the media with different salt concentrations (0%-20%) and pH values (7.0-13.0) to evaluate its salt and alkali tolerance. We then used multiple functional media to examine the growth-promoting function of Bachu 26 and measured the production of indole-3-acetic acid (IAA). The petri dishes with two compartments were used to verify the ability of Bachu 26 to produce acidic volatile substances. Arabidopsis thaliana seedlings were co-cultured with strain Bachu 26 in common culture dishes, based on which the growth-promoting effect of Bachu 26 on A. thaliana seedlings was analyzed. Furthermore, A. thaliana seedlings and Bachu 26 were cultured dividually in the petri dishes with two compartments, based on which the growth-promoting effect of volatile acidic substances produced by Bachu 26 on the seedlings was analyzed. The growth-promoting effect of Bachu 26 on maize seedlings was analyzed by pot experiments. [Results] Strain Bachu 26 was identified as a species of Halomonas and named Halomonas sp. Bachu 26, with the maximum tolerance to 20% salt and pH 11.0. Halomonas sp. Bachu 26 could solubilize organic phosphorus, fix nitrogen, and produce ACC deaminase, IAA, and volatile acidic substances, with the IAA yield reaching 45.885 6 mg/L. Halomonas sp. Bachu 26 significantly increased the fresh weight, lateral roots, taproot length, and leaves of A. thaliana seedlings under saline-alkali stress. In pot experiments, Halomonas sp. Bachu 26 significantly increased the fresh weight of aboveground part, fresh weight of underground part, and plant height of maize under saline-alkali stress. [Conclusion] The newly isolated PGPR strain Bachu 26 has a significant plant growth-promoting effect. The findings provide material and theoretical support for the remediation of saline-alkali soil and development of saline-alkali tolerant plant growth-promoting microbial fertilizers. Furthermore, the results will promote the applied and basic research on Halomonas.