Nigericin was among the first polyether ionophores to be discovered, but its biosynthesis remains obscure. The biosynthetic gene cluster for nigericinhas been serendipitously cloned from Streptomyces sp. DSM4137, and deletion of this gene cluster abolished the production of both nigericin and the closely related metabolite abierixin. Detailed comparison of the nigericin biosynthetic genes with their counterparts in the biosynthetic clusters for other polyketides has prompted asignificant revision of the proposed common pathway for polyether biosynthesis. In particular, we present evidence that in nigericin, nanchangmycin, and monensin, an unusual ketosynthase-like protein, KSX, transfers the initially formed linear polyketide chain to a discrete acyl carrier protein, ACPX, for oxidative cyclization. Consistent with this, deletion of either monACPX or monKSX from the monensin gene cluster effectively abolished monensin A biosynthesis.

为了确定链霉菌702菌株原生质体制备和再生较优组合条件，以链霉菌702菌株为试验材料，试验设计以单因素和多因素多水平的正交试验。在单因素试验结果中探索该菌的对数生长期为35~50 h，在菌丝体培养基中添加1.0%甘氨酸有利于该菌原生质体制备和再生。以影响该菌原生质体制备和再生的菌丝体培养时间、溶菌酶使用浓度、酶解温度和酶解时间的四因素三水平的L₉(3⁴)正交试验结果表明：链霉菌702菌株原生质制备和再生较优组合为A₂B₂C₃D₁，即菌丝体培养时间为43 h，溶菌酶浓度为2.0 mg/mL，酶解温度为37℃，酶解时间60 min，原生质体的制备率和再生率分别达到96.5%和27.8%。本试验为该菌进一步进行原生质体诱变打下良好的基础。

The better composition condition of the factors that affect the formation and regeneration of protoplasts from Streptomyces 702 were investigated. From single factor experiment, the result showed that the logarithmic phase of this strain was 35~50 h. Furthermore, it was propitious to form and regenerate the protoplasts of Streptomyces 702 when 1.0% of glycin was added in medium. The L₉(3⁴) orthogonal experiment was mycelium cultured time, lysozyme concentration, enzymolysis temperature and time. The results indicated that the better assembly condition of formation and regeneration of protoplasts from Streptomyces 702 was A₂B₂C₃D₁ (mycelium cultured for 43 h, 2 mg/mL of lysozyme concentration, enzymolysis at 37℃ for 60 min). The protoplasts rate of forming and regenerating was 96.5% and 27.8%. It laid good foundation for further mutagenesis of the protoplasts.

[目的] 研究不同条件下植物病原真菌对链霉菌702的敏感性变化。[方法] 以水稻纹枯病菌、小麦赤霉病菌和烟草赤星病菌为供试菌，在不同氮(N)、磷(P)、钾(K)水平和不同温度条件下观察3种植物病原真菌对链霉菌702的敏感性变化。[结果] 随着N水平的提高，纹枯病菌菌落直径生长速度减缓，气生菌丝增加，而赤霉病菌与赤星病菌的菌丝生长变化不明显。随N含量的增加，702对3种病菌的抑制率逐渐下降，随着P含量的增加，702对供试菌的抑制率显著增加，随着K含量的增加，702对供试菌的抑制率变化差异不大。当培养温度分别在30、25、25℃时，链霉菌702对水稻纹枯病菌、小麦赤霉病菌和烟草赤星病菌的抑制率最高。[结论] 该研究为链霉菌702有效合理地应用及更好的防治植物病原菌提供了科学依据。

[Objective] To study the sensibility change of plant pathogenic fungi to Streptomyces 702 under different conditions. [Method] With rice sheath blight fungus, wheat scab pathogen and tobacco brown spot pathogen as tested strains, the sensibility changes of 3 kinds of plant pathogenic fungi to Streptomyces 702 under different nitrogen and phosphorous levels and temperature conditions were investigated. [Result] Along with nitrogen level increased, the growth speed of Rhizoctonia solania colony diameter was slowed, while the aerial mycelium was increased. But the changes of mycelium growth of Fusarium graminearum Schwabe and Alternaria alternate Keissler were not obvious. The restrain rate of Streptomyces 702 against the 3 tested strains gradually decreased along with nitrogen content increasing, significantly increased along with phosphorous content increasing, and had little difference along with potassium content increasing. When the cultivation temperatures were at 30, 25 and 25 ℃, the restrain rates of Streptomyces 702 against the 3 tested strains were highest. [Conclusion] The result provides scientific basis for applying Streptomyces 702 to better control plant pathogenic fungi.

研究了链霉菌702所产抗真菌活性物质对水稻纹枯病菌的抑菌机制，结果表明：702对纹枯病菌菌丝生长有强烈的抑制作用，EC50为1.12805 mg/L；能显著的引起菌丝细胞内原生质凝集;对菌核及孢子的萌发有较强的抑制作用，15.11 mg/L和10.64 mg/L完全抑制菌核和孢子的萌发；对孢子形成也有一定的阻碍作用，22.66mg/L完全抑制孢子形成。

The inhibition mechanism of antifungi substance produced by Streptomyces 702 on Rhizocton ia solania in rice was studied. Streptomyces 702 can strongly inhibit mycelium growth and EC50 is 1.12805 mg/L. Streptomyces 702 can obviously result in condensing of the plasma in the mycelium cell and strongly inhibit sclerotium and spore germination, a complete inhibition takes place when the dosage is at the level of 15.11 mg /L and 10.64 mg/L. It has a no table inhibition effect on spore formation, a complete inhibition takes place when the dosage is at the level of 22.66 mg/L.

为了鉴定链霉菌702所产抗细菌物质的化学结构，对纯度为99.47%的抗细菌组分S2组分进行质谱、核磁共振、红外、紫外等波谱学分析。结果表明，链霉菌702所产抗细菌组分S2与放线菌素X2同质，暂命名为红谷霉素。

The structure of the antibacterial component (S2) isolated from Streptomyces 702 was identified as Actinomycin X2 on the basis of the spectroscopic analysis, mainly including MS, NMR, IR and UV. We named it honggumycin.