中文摘要：

【目的】研究极端自然环境对链霉菌线型和环型质粒分布的影响。【方法】从西藏高原采集了20份土壤样品，分离和初步鉴定链霉菌，提取和检测质粒DNA。【结果】从中分离到46株链霉菌，其中有23株菌含有1-4个线型质粒，大小在19-650kb之间，8个菌株含有1-4个环型质粒，大小在4—80kb之间。【结论】西藏土壤来源的链霉菌含有大量的、多样的线型质粒和环型质粒，暗示极端环境中诸如强紫外辐射等可能会引发DNA损伤和修复，进而造成质粒的多样性。

英文摘要：

[Objective] Investigation of occurrence of Streptomyces linear and circular plas- raids in some extremely natural habitats. [Methods] Twenty soil samples from the Tibet pla- teau of China were collected, Streptomyces strains were identified and plasmids were isolated. [Results] Forty-six Streptomyces strains were obtained and, surprisingly, half of them harbored from one to four linear plasmids of 19-650 kb, and eight strains contained from one to four circular plasmids of 4-80 kb. [Conclusion] The abundance and diversity of linear and circular plasmids in Streptomyces strains from Tibet suggests that the extreme environmental stress, such as highly solar radiation, might induce DNA damage and repair to promote formation of varied plasmids.