To visualize transfer of plasmid in Streptomyces during conjugation, we constructed a conjugative plasmid that harbored melC operon encoding an extracellular tyrosinase and placed it in Streptomyces hosts which were defective in expressing the operon. Hyphae of these donors were mixed with hyphae of a plasmidless recipient, which could express melC, and plated on a solid medium supplemented with tyrosine. After 8 to 9 h of incubation, melanin started to appear in the mating mixture, indicating that the plasmid had entered the recipient and started to synthesize tyrosinase, which in turn catalyzed the formation of melanin. This visual monitoring system allows quick demonstration of conjugal transfer without tedious genetic or biochemical procedure commonly used. It may be applied to most Streptomyces species and may also be used for monitoring chromosome transfer.

中文翻译：

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黑色素的产生是链霉菌中结合转移的视觉指示。

为了可视化结合过程中质粒在链霉菌中的转移，我们构建了一个结合质粒，该质粒带有编码细胞外酪氨酸酶的melC操纵子，并将其置于表达该操纵子的链霉菌宿主中。这些供体的菌丝与无质粒受体的菌丝混合，可以表达melC，然后涂在补充有酪氨酸的固体培养基上。温育8至9小时后，黑色素开始出现在交配混合物中，表明该质粒已进入受体并开始合成酪氨酸酶，进而催化黑色素的形成。这种视觉监控系统可以快速演示夫妻转移，而无需通常使用繁琐的遗传或生化程序。它可以应用于大多数链霉菌种，也可以用于监测染色体转移。