在过去几十年里，细菌质粒的生物学功能包括复制、接合转移、拷贝数调控、功能基因等方面的研究取得了大量的进展，唯独质粒群体的进化及其分子机制的研究主要是理论推测，实验进展十分缓慢。我们前期发现一块来自湖南郴州郊区的高浓度重金属污染土壤中链霉菌是可培养的优势菌群，这些链霉菌富含线型质粒和环型质粒。在本申请项目中，我们拟将该土样点分离和鉴定的所有链霉菌质粒（已发表论文的除外）进行克隆和测序，实验鉴定复制基因，以及与质粒共整合的噬菌体的功能。进一步通过对亲缘关系近的菌株进行人工进化实验和新生质粒再测序，初步确定这些链霉菌质粒群体进化的几种可能的分子机制。

In past several decades, a lot of progresses have been made on plasmid biology including replication, transfer, copy number control, functional genes etc, while a few reports on plasmid evolution which mainly depends on theoretical speculations rather than experiments. In previous work, we found that abundance of Streptomyces strains including their endogenous linear and circular plasmids in one heavy-metals contaiminated soil sample from Chenzhou in Hunan province. In this application, we will sequence all the plasmids, verify their replication loci and possible phage functions. Furthermore, we will co-culture two close related strains and re-sequence the newly formed plasmids. On comparison of all plasmid sequences, possible mechanisms on Streptomyces plasmid evolution would be provided.