产生变活霉素的变株的分离与初步鉴别

对天然无抗菌活性的链霉菌1254菌株进行诱变．获导了二株有抗菌活性的变株。变株113产生的抗生素为一组新蒽环类化合物．有抗病毒活性，定名为变活霉素。变株2—6产生碱性永溶性物质。初步实验结果表明，原株1254及变株2-6均是胞壁类型1，为链霉菌属。变株113为胞壁类型Ⅳ，不含有枝菌酸。原株1254与变株113的阻断变株共合成的产物与变活霉素相局，以放线紫红素聚酮合成酶基因act1为探针与原株1254的总DNA进行Southern杂交为阳性。根据这二个实验的结果推断，在1254菌株中可能存在一条变活霉素的合成途径，但有的基因处于未表达状态，诱发突变使其被活化。

Isolation and characterization of mutactimycin-producing mutant]

Natural non-antibiotic producing Streptomyces sp. 1254 was mutagenized by UV irradiation and two active mutants were isolated. Mutant 113 produced novel anthracycline compounds designated mutactimycins. Mutactimycin A was active against the bacteriophage of Bac. subtilis and some viruses in tissue culture. The mutant 2-6 synthesized a basic water-soluble antimicrobial antibiotic. Chemical analysis of the whole cell hydrolysate and the morphological characterization showed that the strain 1254 and its mutant 2-6 were of chemotype I, belonging to the genus of Streptomyces, and the mutant 113 was of chemotype IV without mycolic acid. Co-synthesis test of strain 1254 and a blocked mutant of strain 113 gave the active compounds identical with mutactimycins. Using the actI gene as a probe, the Southern hybridization revealed homology between the actinorhodin polyketide biosynthase gene and the total DNA of the strain 1254. Based on these data it was deduced that Streptomyces sp. 1254 should have a biosynthesis pathway for mutactimycin, but some of its genes might fail in expression and mutagenesis would make the silent gene(s) active.