Isolation and identification of salt-tolerant growth-promoting bacteria capable of remediating secondary salinized soils of greenhouses

Abstract:

[Background] The prevalence of secondary salinization in soil poses a significant constraint on the sustainable development of protected vegetable production. [Objective] To screen out the salt-tolerant growth-promoting microbial strains and provide bacterial resources for remediating secondary salinized soils in greenhouses. [Methods] The LB medium with 5% salt was used to screen out the salt-tolerant strains from the soil samples of vegetable greenhouses by the dilution-plate coating method. The growth-promoting ability of each strain was determined by the seed immersion method. The morphological characteristics, physiological and biochemical properties, and 16S rRNA gene sequence were used to identify the strains. The salt tolerance and growth-promoting effect of each strain were measured by quantitative and qualitative methods. Pot experiments were carried out to examine the remediation effect of each strain on salinized soil samples and the cucumber growth-promoting effect. [Results] Fifty-eight strains of salt-tolerant bacteria were isolated from 37 salinized soil samples. Among them, five strains, YQ-1-8, SN-1-4, 3A-2, L1-2, and L3-3, increased the simplified activity index of cucumber by more than 15%, and all of them had growth-promoting effects on cucumber seedlings exposed to 0.3% salt. However, the growth-promoting effect decreased with the increasement of the salt concentration. YQ-1-8 was identified as B acillus velezensis, SN-1-4 as Arthrobacter arilaiti, 3A-2 as B. marisflavi, L1-2 as B. cereus, and L3-3 as B. aryabhattai. Strain 3A-2 was capable of solubilizing organophosphorus and producing IAA and exopolysaccharide. The results of pot experiments showed that 3A-2 at 1×10⁷ cfu/g increased the stem thickness, plant height, aboveground fresh weight, aboveground dry weight, and chlorophyll by 12.39%, 14.31%, 30.92%, 38.46%, and 9.06%, respectively. In addition, the strain increased the content of available nitrogen and available potassium and decreased the pH, electrical conductivity, and total salt content in soil (P<0.05). [Conclusion] Strain 3A-2 with salt tolerance and growth-promoting effect can serve as a candidate for the development of microbial agents for the recommendation of secondary salinized soils.