Isolation and characterization of halotolerant phosphate-solubilizing microorganisms from saline soils
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Halotolerant phosphate-solubilizing microorganisms (PSMs) capable of producing plant-growth-promoting traits were grown on salt medium containing Ca3(PO4)2 or egg yolk. The number of colonies on plates with Ca3(PO4)2 was higher than that on plates with egg yolk. Further, a total of 42 PSM isolates were purified. The majority were Bacillus spp., while one Providencia rettgeri strain was confirmed, for the first time, as a PSM. All PSMs had a phosphate-solubilizing index (PSI) between 1.1 and 2.58 and a strong capacity for dissolving calcium phosphate between 2.25 and 442 mg·L−1. In contrast, these PSMs were less effective when dissolving aluminum phosphate, ferric phosphate and lecithin. Isolates were also tested for growth-promoting substances. The results showed that all isolates were able to secrete indole-3-acetic acid in amounts ranging from 2.7 to 31.8 mg·L−1 and exopolysaccharide within the range 74.3 and 225.7 mg·L−1. Only 12 siderophore-producing strains with siderophore units of 1.9–42.1% were detected. Among them, ten isolates with solubilization rates greater than 200 mg·L−1 and relatively high NaCl tolerance (1.5 M) were classified as candidate PSMs. Eight different organic acids with different contents were detected in the culture filtrates, and propionic and oxalic acids have been proposed as the main mechanisms for solubilization. The ten isolates have the potential for use as bioinoculants to protect plants in saline environments.
KeywordsSaline soil Phosphate-solubilizing microorganisms Organic acids Plant growth-promotion traits
This study was supported with grants from the State Key Laboratory of Urban Water Resource and Environment (2017DX15), the National Ten Thousand Youth Talents Plan of 2014, China Agriculture Research System (CARS14), the National Natural Science Foundation of China (31000728 and 31200211), and the Natural Science Fund of Shandong Province (ZR2014YL011 and ZR2014YL012).
All authors have seen and approved the manuscript and its contents, and declare they are aware of the responsibilities connected to authorship. Pei-shi Qi and Xiao-yuan Chi designed the study and performed critical revision of the manuscript; Huan-huan Jiang and Ming-na Chen performed the experiment and data analysis; Huan-huan Jiang composed the manuscript; Tong Wang and Na Chen collected the samples; and Mian Wang and Li-juan Pan guided the research.
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
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