Distributive Conjugal Transfer: a New Paradigm and Benchmark for Bacterial Horizontal Gene Transfer

从一种细菌到另一种细菌的DNA转移加速了新菌株和新物种的进化。消极的一面是，DNA转移可能促进抗生素抗性基因的传播，使传染病的治疗策略复杂化。从积极的方面来看，DNA转移也可以创造出具有改进的有益特性的细菌菌株，例如修复石油污染的土壤。分枝杆菌是细菌王国的一个分支，包括病原体和居住在棕地土壤中的物种。一种新型的高效DNA转移过程，其中两个细胞似乎沿着整个染色体交换DNA片段，已经描述了一种常见的实验室分枝杆菌物种。目前的项目将确定参与这一过程的基因，同时测试远亲分枝杆菌是否能参与这种转移。该项目将为本科生和当地高中教师提供获得研究经验的机会。共轭DNA转移已经在耻垢分枝杆菌中被描述，产生杂交的基因组，是亲本菌株的混合物。分布共轭转移（distributed Conjugal Transfer， DCT）与传统的基于质粒的接合系统在产生镶嵌基因组和机制上都有所不同，并且通常在质粒转移系统中发现的蛋白质在分枝杆菌中不存在。一个决定供体或受体活性的交配身份位点（中间）已经被定位到一个嵌入在编码ESX-1分泌装置的25个基因位点中的6个基因簇。研究人员将分析组成mid的6个基因对建立交配身份的贡献，它们与ESX-1分泌的功能关联，以及它们对与交配伴侣共培养的转录途径的影响。DCT还将在其他耻垢分枝杆菌分离株和其他分枝杆菌种类中进行测试。新分离株的基因组测序将为鉴定作为DCT标志的嵌合体提供比较数据，并为实验室产生的转接合物提供参考序列。这一目标的成功实施将为分枝杆菌属中DCT对基因流的影响提供更广泛的视角，并为中位点的关键基因提供额外的基因型/表型信息。

The transfer of DNA from one bacterium to another accelerates the evolution of new strains and species. On the negative side, DNA transfer could facilitate the spread of antibiotic resistance genes, complicating infectious disease treatment strategies. On the positive side, DNA transfer could also create bacterial strains with improved beneficial properties, such as the remediation of petroleum-contaminated soil. Mycobacteria are a branch of the bacterial kingdom that includes both pathogens and brownfield soil-dwelling species. A novel kind of highly effective DNA transfer process, in which two cells appear to swap DNA fragments along the whole chromosome, has been described for a common laboratory mycobacterial species. The current project will identify the genes involved in that process, also testing whether distantly related mycobacteria can partake in such a transfer. The project will provide opportunities for undergraduate students and local high school teachers to gain experience in research.Conjugal DNA transfer has been described in Mycobacterium smegmatis, generating transconjugant genomes that are mixtures of the parental strains. Distributive Conjugal Transfer (DCT) differs from traditional plasmid-based conjugation systems both in creating mosaic genomes and in mechanism, and proteins usually found in plasmid transfer systems are absent from mycobacteria. A mating identity locus (mid), which determines donor or recipient activity, has been mapped to a six-gene cluster embedded within a 25-gene locus that encodes the ESX-1 secretion apparatus. The six genes comprising mid will be analyzed for their contribution to establishing mating identity, their functional association with ESX-1 secretion, and their impact on transcriptional pathways that respond to co-culture with a mating partner. DCT will also be tested in other isolates of M. smegmatis, and in other mycobacterial species. Genome sequencing of new isolates will provide comparative data for identifying the mosaicism that is a hallmark of DCT, and provide reference sequences for transconjugants generated in the laboratory. Successful implementation of this objective will provide a broader view of the impact of DCT on gene flow in the Mycobacterium genus, and provide additional genotype/phenotype information for the critical genes of the mid locus.