产胞外多糖菌株的分离鉴定及其功能研究

微生物产生的胞外多糖(exopolysaccharides, EPS)可促进大粒径土壤团聚体形成，高产EPS的菌株在土壤改良、促进作物生长方面具有较好的应用前景。【目的】从土壤样品中筛选高产胞外多糖的细菌，研究其在土壤改良、环境适应性、广谱抗病等方面的功能，为制备土壤改良型功能菌剂提供候选菌株。【方法】采用蒽酮硫酸法测定菌株胞外多糖的产量，通过形态学观察、生理生化试验及16S rRNA基因序列测定确定其分类地位，结合土壤培养试验研究菌株对土壤团聚体形成的影响。【结果】获得3株胞外多糖产量大于500 mg/L的细菌，经鉴定A-5为地衣芽孢杆菌(Bacillus licheniformis)，XJ-3为萎缩芽孢杆菌(Bacillus atrophaeus)，KW3-10为耐盐芽孢杆菌(Bacillus halotolerans)。菌株A-5、XJ-3、KW3-10处理后，土壤大团聚体(>0.25 mm)含量较对照分别提高了4.07、2.14和3.16倍。3株菌株对疮痂链霉菌(Streptomyces scabies)、尖孢镰刀菌(Fusarium oxysporum)、茄链格孢菌(Alternaria solani)和立枯丝核菌(Rhizoctonia solani)等多种植物病原菌具有明显的抑制效果，可耐受pH为5-9和NaCl含量1%‒9%的盐碱环境，促进植物生长，其中KW3-10的代谢产物中IAA含量为25.58 mg/L。【结论】菌株A-5、XJ-3、KW3-10可显著促进土壤团粒结构形成，具有较好的广谱抗病性和促生长特性，可作为高效复合功能菌剂的候选菌株。

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

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.