Conjugative transfer of chromosomal DNA in Streptomyces: molecular principle and its relevance for the evolution of genomes

接合，通过细胞间的直接接触在细菌之间转移DNA是水平基因转移(HGT)的主要途径。产生抗生素的土壤细菌链霉菌属开发了一种独特的连接系统，以近100%的效率转移双链质粒分子。这种转移是由单一的质粒编码蛋白DNA转位酶TRAb引导的，它结合到特定的非编码质粒区(CLT)。质粒转移与染色体DNA的同时转移有关。这种染色体动员能力(CMA)几十年来一直被广泛用于建立链霉菌染色体的遗传连锁图谱，但其潜在的机制尚不清楚。我们观察到百万碱基大小的DNA片段的转移，并表明链霉菌染色体利用了质粒编码的转移装置，从而充当了一个可移动的遗传元件。我们旨在通过鉴定和鉴定TRAb的染色体CLT样结合部位以及通过插入跟踪(TN-seq)揭示参与CMA的其他细胞功能来阐明CMA的分子原理。我们希望通过转接子的全基因组测序来确定转移的染色体DNA的大小和程度，并研究CMA与生物合成基因簇和抗性决定因素的转移和传播的相关性。

Conjugation, the transfer of DNA between bacteria by direct cell-to-cell contact is a major route of horizontal gene transfer (HGT). Antibiotic producing soil bacteria of the genus Streptomyces developed a unique conjugation system, transferring double-stranded plasmid molecules with nearly 100 % efficiency. This transfer is directed by a single plasmid-encoded protein, the DNA-translocase TraB, which binds to a specific non-coding plasmid region (clt). Plasmid transfer is associated with the simultaneous transfer of chromosomal DNA. This Chromosome Mobilizing Ability (CMA) has been extensively used for decades to establish genetic linkage maps of Streptomyces chromosomes, however its underlying mechanism is completely unknown. We observed the transfer of megabase-sized DNA-fragments and showed that the Streptomyces chromosome exploits the plasmid-encoded transfer apparatus, thereby acting itself as a mobile genetic element. We aim to elucidate the molecular principles of CMA by identifying and characterizing chromosomal clt-like binding sites of TraB and by revealing other cellular functions involved in CMA by insertion tracking (Tn-seq). We want to determine the size and the extent of the transferred chromosomal DNA by whole genome sequencing of transconjugants and study the relevance of CMA for the transfer and dissemination of biosynthetic gene clusters and resistance determinants.