短枝木麻黄根际放线菌及其抗细菌活性

目的 分离并鉴定短枝木麻黄根际土壤中的放线菌，测定短枝木麻黄根际放线菌的抗细菌活性，并从中筛选出活性放线菌菌株。 方法 采用热击稀释法分离短枝木麻黄根际土壤中的放线菌，通过形态学观察和分子生物学相结合的方法对分离得到的放线菌菌株进行鉴定，采用薄层层析（TLC）-生物自显影法测定短枝木麻黄根际放线菌次生代谢产物对不同供试细菌的抑制活性，进一步采用高效液相色谱（HPLC）分析根际放线菌乙酸乙酯层提取物中次生代谢产物的情况。 结果 从短枝木麻黄根际土壤中共分离鉴定得到12株放线菌，均为链霉菌属（Streptomyces sp.）放线菌，最大相似度均在97%以上。活性测定的结果表明：菌株S. spinosus Ceaf-4和S. chattanoogensis Ceaf-12对木麻黄青枯病菌（Ralstonia solanacearum）表现出较强的抑制活性，抑菌斑的直径均在10 mm以上；菌株S. spinosus Ceaf-4对大肠杆菌（Escherichia coli）和溶血葡萄球菌（Staphylococcus haemolyticus）的抑菌斑直径也大于10 mm。高效液相色谱分析的结果表明，菌株S.spinosus Ceaf-4和S. chattanoogensis Ceaf-12均含有丰富的次生代谢产物，但次生代谢产物的类型和相对含量均存在明显差异。 结论 短枝木麻黄根际土壤中存在以链霉菌属为优势种群的放线菌，菌株S. spinosus Ceaf-4和S. chattanoogensis Ceaf-12对木麻黄青枯病菌表现出较强的抑制活性且含有丰富的次生代谢产物，可作为候选菌株进一步发掘其抗菌活性成分。

Antibacterial Activities of Rhizospheric Actinomycetes Associated with Casuarina equisetifolia

Objective This study aimed to isolate and identify actinomycetes in rhizospheric soil of Casuarina equisetifolia, determine the antibacterial activity of the rhizospheric actinomycetes, and screen out the actinomycetes isolates with antimicrobial activities. Methods The actinomycetes in the rhizospheric soil of C. equisetifolia were isolated by heat strike dilution method. The actinomycetes isolates were further identified by combining morphological observation with molecular biology method. The antibacterial activities of secondary metabolites produced by the rhizospheric actinomycetes against different bacteria were determined using TLC-bioautography assay. The secondary metabolites in the ethyl acetate layer of rhizospheric actinomycetes were analyzed by HPLC (high performance liquid chromatography). Results A total of twelve actinomycetes strains were isolated and identified from the rhizospheric soil of C. equisetifolia, all of which were the genus of Streptomyces sp., and the maximum similarities were all above 97%. S. spinosus Ceaf-4 and S. chattanoogensis Ceaf-12 had stronger antibacterial activity against Ralstonia solanacearum, and the diameters of antibacterial spots were more than 10 mm. The antibacterial spot diameters of strain S. spinosus Ceaf-4 against Escherichia coli and Staphylococcus haemolyticus were also greater than 10 mm. In addition, S. spinosus Ceaf-4 and S. chattanoogensis Ceaf-12 both contained abundant secondary metabolites, but there were significant difference in the types and relative contents of secondary metabolites. Conclusion There are actinomycetes with Streptomyces sp. as the dominant population in the rhizospheric soil of C. equisetifolia. S. spinosus Ceaf-4 and S. chattanoogensis Ceaf-12 show the stronger inhibitory activity against R. solanacearum and contain abundant secondary metabolites. They can be used as candidate active strains to further explore their antibacterial active components.