Streptomycetes are high G+C Gram-positive, antibiotic-producing, mycelial soil bacteria. The 8.7-Mb
Streptomyces coelicolor
genome was previously sequenced by using an ordered library of Supercos-1 clones. Here, we describe an efficient procedure for creating precise gene replacements in the cosmid clones by using PCR targeting and λ-Red-mediated recombination. The cloned
Streptomyces
genes are replaced with a cassette containing a selectable antibiotic resistance and
oriT
RK2
for efficient transfer to
Streptomyces
by RP4-mediated intergeneric conjugation. Supercos-1 does not replicate in
Streptomyces
, but the clones readily undergo double-crossover recombination, thus creating gene replacements. The antibiotic resistance cassettes are flanked by yeast FLP recombinase target sequences for removal of the antibiotic resistance and
oriT
RK2
to generate unmarked, nonpolar mutations. The technique has been used successfully by >20 researchers to mutate around 100
Streptomyces
genes. As an example, we describe its application to the discovery of a gene involved in the production of geosmin, the ubiquitous odor of soil. The gene, Sco6073 (
cyc2
), codes for a protein with two sesquiterpene synthase domains, only one of which is required for geosmin biosynthesis, probably via a germacra-1 (10)
E,5E
-dien-11-ol intermediate generated by the sesquiterpene synthase from farnesyl pyrophosphate.
链霉菌是高G+C革兰氏阳性的、产生抗生素的、菌丝状土壤细菌。先前使用Supercos-1克隆有序文库对8.7-Mb的链霉菌基因组进行了测序。在这里,我们描述了一种有效的程序,通过使用PCR定向和λ-Red介导的重组,在cosmid克隆中创建精确的基因替换。克隆的链霉菌基因被含有可选择的抗生素耐药性和oriTRK2的引物替换,以便通过RP4介导的种间接合作用高效地转移到链霉菌中。Supercos-1不会在链霉菌中复制,但克隆体容易经历双交叉重组,从而创建基因替换。抗生素耐药性引物被酵母FLP重组酶靶序列包围,以去除抗生素耐药性和oriTRK2,生成未标记的非极性突变。这种技术已被20多名研究人员成功地用于突变约100个链霉菌基因。例如,我们描述了其在发现参与土壤普遍气味geosmin产生的基因方面的应用。该基因Sco6073(cyc2)编码一个具有两个倍半萜合成酶结构域的蛋白质,其中只有一个结构域对于geosmin生物合成是必需的,可能通过来自法尼基焦磷酸的倍半萜合成酶产生的germacra-1(10)E,5E-dien-11-ol中间体实现。