三种荒漠灌木根际可培养固氮细菌类群及其固氮和产铁载体能力

【目的】揭示西鄂尔多斯荒漠孑遗灌木四合木(Tetraena mongolica)、沙冬青(Ammopiptanthus mongolicus)、白刺(Nitraria tangutorum)根际可培养固氮细菌类群,分析固氮酶活性和产铁载体能力,以期为认识和利用荒漠植物根际促生细菌提供依据。【方法】以Ashby无氮培养基、采用涂布划线法分离纯化根际固氮细菌;基于16S r RNA基因分析类群组成;以乙炔还原方法测定固氮酶活性;以铬天青S蓝色平板定性筛选产铁载体菌株,以分光光度计法定量产铁载体能力。【结果】共分离出固氮细菌22株,分别属于3个门与9个属,其中变形菌门(Proteobacteria,82%)为绝对优势门,假单胞菌属(Pseudomonas,27.27%)为优势属;Rhizobium和Bacillus分别是沙冬青和四合木的独有属,而白刺独有属有Enterobacter、Stenotrophomonas和Paenibacillus;10株在无氮培养基上生长迅速,它们的固氮酶活性在871.71-3 383.09 nmol C2H4/(H·Culture)之间,并且其中有7株具有产铁载体能力,其产铁载体的As/Ar值范围为0.35-0.79。【结论】鄂尔多斯荒漠珍稀孑遗灌木植物根际固氮细菌类群多样,植物间差异明显,包含多种高固氮酶活性和产铁载体能力的固氮细菌,可作为植物生长促进根际细菌的重要来源。

Cultivable diazotrophic community in the rhizosphere of three desert shrubs and their nitrogen-fixation and siderophore-producing capabilities

Objective] To reveal the cultivable diazotrophic communities in the rhizosphere of three relict shrubs of Tetraena mongolica, Ammopiptanthus mongolicus and Nitraria tangutorum in Western Ordos and the bacterial capabilities for nitrogen-fixation and siderophore-producing, and finally to provide basis for understanding and utilizing the desert plant growth-promoting rhizobacteria. Methods] Using Ashby medium nitrogen-free, the nitrogen-fixation bacteria strains were isolated and purified by the plate spread and streak technique; 16S rRNA gene was applied to classify the isolates and reveal the community composition. The nitrogenase activities of rapid-growing strains were analyzed through acetylene reduction assay. To screen siderophore-producing strains and their capability of siderophore production, chrome azurol S (CAS) blue plate and spectrophotometer were used for qualitative screening the strains and quantitative determination of their products, respectively. Results] A total of 22 rhizospheric diazotrophs were isolated and classified into 3 phyla and 9 genera and they were predominated by the phylum Proteobacteria (82%) and the genus Pseudomonas (27.27%). The genus Rhizobium and Bacillus was solely found associated with Ammopiptanths mongolicus and Teraena mongolica respectively, whereas Enterobacter, Stenotrophomonas and Paenibacillus only with Nitraria tangutorum. Ten strains could rapidly grow on the nitrogen-free medium and they possessed nitrogenase activity in the range of 871.71 to 3 383.09 nmol C2H4/(H?culture). Seven of the 10 strains could produce siderophore and the producing capability (As/Ar value) was ranged from 0.35 to 0.79. Conclusion] the cultivable rhizospheric diazotroph in the rhizosphere soil of the relict shrubs in Ordos desert was highly diverse and markedly different between the shrubs. Most of these diazotrophs have both high nitrogen-fixation and siderophore-producing capability. Thus, they could be useful as plant growth-promoting rhizobacteria.