Isolation, identification, and functional characterization of exopolysaccharide-producing strains

Abstract:

Exopolysaccharides (EPS) produced by microorganisms can promote the formation of large soil aggregates. EPS-producing strains have good application prospects in improving soil and promoting crop growth. [Objective] We isolated the bacteria with high yields of exopolysaccharides from soil samples and studied their soil-improving function, environmental adaptability, and broad-spectrum disease resistance, aiming to provide candidate strains for the preparation of soil-improving microbial agents. [Methods] The yield of EPS was determined by anthrone-sulfuric acid method. The taxonomic status of the strain was determined by morphological observation, physiological and biochemical tests, and 16S rRNA gene sequencing. Soil culture experiments were carried out to evaluate the effect of the strain on the formation of soil aggregates.[Results] Three strains of bacteria with EPS yields greater than 500 mg/L were obtained. A-5 was identified as Bacillus licheniformis, XJ-3 as B. atrophaeus, and KW3-10 as B. halotolerans. After treatment with these strains, the content of soil macroaggregates (>0.25 mm) increased by 4.07, 2.14, and 3.16 times, respectively. The three strains exerted significant inhibitory effects on plant pathogens such as Streptomyces scabies, Fusarium oxysporum, Alternaria solani, and Rhizoctonia solani. They could tolerate the saline-alkali environment with pH 5-9 and NaCl content of 1%-9% and promoted plant growth. The content of indole acetic acid in the metabolites of KW3-10 was 25.58 mg/L. [Conclusion] Strains A-5, XJ-3, and KW3-10 can significantly promote the formation of soil aggregates and demonstrate broad-spectrum disease resistance and remarkable growth-promoting performance, serving as candidates for the preparation of efficient compound microbial agents.