Gene Transfer Agents in the Oceans-What are they doing?

海洋微生物数量丰富，种类繁多。是什么推动了这种多样性？突变和自然选择似乎只占了其中的一部分。基因组测序的能力表明，横向基因转移(LGT)，即无关微生物之间的基因不分青红皂白的移动，在产生多样性方面发挥着重要作用，现在被公认为微生物进化的主要驱动力。在这个项目中，南佛罗里达大学的Paul和McDaniel认为，原核生物基因转移的三种已知机制(转导、转化和接合)似乎不可能也不可能在海洋环境中以足够的频率发生，从而成为微生物多样性的重要驱动因素。为了研究导致微生物多样性的其他因素，这些研究人员将评估一种新形式的LGT的意义，这种新型LGT涉及一种鲜为人知的称为基因转移剂(GTA)的颗粒。GTA是编码在特定细菌群体(α-变形杆菌)基因组中的噬菌体颗粒，包装宿主基因组DNA的随机片段。这些颗粒不会裂解宿主，而是将先前宿主的DNA注入新宿主，然后转移的DNA整合到新宿主的基因组中。基因组测序最近揭示了GTA在α-蛋白细菌基因组中的普遍存在，一项对102个海洋细菌基因组的调查表明，20个(20%)含有推定的GTA。玫瑰杆菌是一种α-蛋白细菌，可占沿海环境中细菌总数的25%，其丰富的GTA可能使GTA成为海洋环境中LGT的最重要机制。这些研究人员想知道：如果GTA在细菌基因组中大量存在，它们在做什么？这些研究人员将使用已知的宿主和已知的遗传示踪剂，如质粒，来检查海洋GTA的基因转移能力。他们还将通过使用针对特定GTA的标记基因诊断，确定海洋沿海人口中是否存在含有GTA的细菌。最后，研究人员将评估GTA在海洋细菌本土种群内转移基因的潜力。在这些实验中，这些研究人员将跟踪DNA在实验室菌株和本土细菌之间的移动，然后在本土细菌种群之间的移动，以估计海洋中GTA进行基因转移的自然速度。Paul和McDaniel的这项研究的长期目标是阐明一种鲜为人知的LGT形式在海洋环境中的作用，为后续研究通过GTA进行的基因流动和控制海洋微生物多样性的因素奠定基础。作为这一项目的一部分，私人投资促进机构将开展一些外联活动。他们将开发关于GTA指标的高中实验室模块，并将在佛罗里达州皮内拉斯县种族多元化学校的课堂上使用这些模块。他们将继续参加女孩海洋夏令营，这是一个由USF海洋科学学院主办的为期三周的夏令营，每年夏天为九年级的学生举办。PI计划在这些实验活动中增加一个GTA探测器组件。

Marine microorganisms are abundant and diverse. What drives this diversity? Mutation and natural selection appear to account for only a portion of it. The ability to sequence genomes is demonstrating that lateral gene transfer (LGT), the indiscriminant movement of genes between unrelated microbes, plays a significant role in generating diversity, and it is now recognized as a major driving force in microbial evolution. In this project, Paul and McDaniel of the University of South Florida argue that the three known mechanisms of prokaryotic gene transfer (transduction, transformation, and conjugation) appear to be unable and unlikely to occur with sufficient frequency in the marine environment to be significant drivers of microbial diversity. In order to examine other factors contributing to microbial diversity, these investigators will be evaluating the significance of a novel form of LGT which involves little-understood particles called Gene Transfer Agents (GTAs). GTAs are phage-like particles encoded in the genomes of particular groups of bacteria (alpha-proteobacteria) that package random fragments of host genomic DNA. These particles do not lyse their host, but rather inject their prior host's DNA into a new host, and the transferred DNA then integrates into the new host's genome. Genomic sequencing has recently revealed the prevalence of GTAs in alpha-proteobacterial genomes, and a survey of 102 marine bacterial genomes indicated twenty (20%) contained putative GTAs. The abundance of GTAs in the Roseobacter lineage, an alpha-proteobacteria group that can comprise up to 25% of the bacteria in coastal environments, may make GTAs the most important mechanism of LGT in the marine environment. These researchers want to know: if GTAs are abundant in bacterial genomes, what are they doing? These investigators will be examining the gene transfer capability of marine GTAs by using known hosts and known genetic tracers, like plasmids. They will also determine the occurrence of GTA-containing bacteria in marine coastal populations by using marker genes diagnostic for specific GTAs. Finally, the investigators will evaluate the potential for GTAs to transfer genes within indigenous populations of marine bacteria. In these experiments, these investigators will track the movement of DNA between lab strains and indigenous bacteria and then between populations of indigenous bacteria to estimate the natural rate of gene transfer by GTAs in the ocean. The longterm goal of this research by Paul and McDaniel is to elucidate the role of a little understood form of LGT in the marine environment, setting the stage for follow on studies on the flux of genes via GTAs and on what controls microbial diversity in the oceans. The PIs will carry out a number of outreach activities as a part of this project. They will be developing high school lab modules on GTA indicators and will be using them in classes from ethnically and racially diverse schools in Pinellas County, FL. They will continue their participation in the Oceanography Camp for Girls, a three week day camp each summer, hosted by the USF College of Marine Science, for students entering the 9th grade. THe PIs plan to add a GTAs detector component to these lab activities.