Isolation and functional identification of a growth-promoting rhizobacterial strain of Alkalibacterium

Abstract:

[Background] Soil salinization is a global problem, and there are a large number of undeveloped functional microorganisms in the rhizosphere of salt tolerant plants, such as plant growth-promoting rhizobacteria (PGPR). These microorganisms can help plants resist salt alkali stress and promote plant growth through their own growth promoting functions. [Objective] This study screened plant growth-promoting rhizobacteria (PGPR) with salt-alkali tolerance and evaluated their growth-promoting effects, aiming to provide candidate strains for the development of microbial fertilizers for saline-alkaline land. [Methods] A bacterial strain Bachu49 with salt-alkali tolerance was isolated from the rhizosphere soil of wild Tamarix chinensis in Kashgar Prefecture of Xinjiang. This strain Bachu49was identified based on morphological, physiological, and biochemical characteristics and 16S rRNA gene sequence. Multiple media for functional identification were used to examine the growth-promoting effects [solubilizing potassium, fixing nitrogen, solubilizing phosphorus, synthesizing indole-3-acetic acid (IAA), secreting 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and producing siderophores] of Bachu49. The Petri dish with two compartments was used to examine the production of volatile acid substances by Bachu49. Finally, the effects of Bachu49 on the growth of Arabidopsis and maize seedlings were analyzed by plate and pot experiments, respectively. [Results] A strain Bachu49 with salt-alkali tolerance was isolated from the soil samples. This strain was identified as Alkalibacterium sp. and named Alkalibacterium sp. Bachu49. Strain Bachu49 had the effects of fixing nitrogen, solubilizing organic phosphorus, and synthesizing IAA. It survived within the salt concentration of 0−160 g/L and pH 7.0−11.0 and showed the ability of reducing alkali. At pH 8.0, 9.0, and 10.0, the alkali reduction rates of Bachu49 were 9.75%, 15.56%, and 20.60%, respectively. Strain Bachu49 promoted the growth of Arabidopsis and maize seedlings under salt-alkali stress. Specifically, at pH 8.0 and 2 mmol/L NaHCO₃, inoculation with strain Bachu49 increased the root length, number of lateral roots, fresh weight, and number of leaves of Arabidopsis by 239.86%, 1 952.83%, 389.71%, and 91.23%, respectively. Inoculation of this strain increased the underground fresh weight of maize seedlings by 10.14% in the presence of 15 g/kg salt-alkali, and it increased the aboveground fresh weight, stem diameter, and plant height of maize seedlings by 42.04%, 23.14%, and 40.91%, respectively, under 30 g/kg salt-alkali stress. [Conclusion] Alkalibacterium sp. Bachu49 has excellent salt-alkali tolerance and plant-growth promoting effects under salt-alkali stress. This study provides a candidate strain and a theoretical basis for the future development of specialized microbial fertilizers for saline-alkali soil.