Wright Meredith S, Baker-Austin Craig, Lindell Angela H, Stepanauskas Ramunas, Stokes Hatch W, McArthur J Vaun
Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, USA.
ISME J. 2008 Apr;2(4):417-28. doi: 10.1038/ismej.2008.8. Epub 2008 Feb 14.
The acquisition of new genetic material via horizontal gene transfer allows bacteria to rapidly evolve. One key to estimating the contribution of horizontal gene transfer to bacterial evolution is to quantify the abundance of mobile genetic elements (MGEs) in bacterial communities under varying degrees of selective pressure. We quantified class 1 integrase (intI1) gene abundance in total community DNA extracted from contaminated and reference riverine and estuarine microhabitats, and in metal- or antibiotic-amended freshwater microcosms. The intI1 gene was more abundant in all contaminant-exposed communities indicating that relative gene transfer potential is higher in these communities. A second key to assessing the contributions of MGEs to bacterial evolution is to examine the structure and function of the MGE-associated gene pool. We determined that the gene cassette pool is a novel and diverse resource available for bacterial acquisition, but that contamination has no discernible effect on cassette richness. Gene cassette profiles were more similar within sites than among sites, yet bacterial community profiles were not, suggesting that selective pressures can shape the structure of the gene cassette pool. Of the 46 sequenced gene cassette products, 37 were novel sequences, while the 9 gene cassettes with similarity to database sequences were primarily to hypothetical proteins. That class 1 integrons are ubiquitous and abundant in environmental bacterial communities indicates that this group of MGEs can play a substantial role in the acquisition of a diverse array of gene cassettes beyond their demonstrated impact in mediating multidrug resistance in clinical bacteria.
通过水平基因转移获得新的遗传物质可使细菌快速进化。估计水平基因转移对细菌进化贡献的一个关键是量化在不同程度选择压力下细菌群落中可移动遗传元件（MGEs）的丰度。我们对从受污染和对照的河流及河口微生境中提取的总群落DNA，以及在添加金属或抗生素的淡水微宇宙中，对1类整合酶（intI1）基因的丰度进行了量化。在所有暴露于污染物的群落中，intI1基因更为丰富，表明这些群落中的相对基因转移潜力更高。评估MGEs对细菌进化贡献的另一个关键是研究与MGE相关的基因库的结构和功能。我们确定基因盒库是细菌可获取的一种新颖且多样的资源，但污染对盒丰富度没有明显影响。基因盒谱在各采样点内比在各采样点间更为相似，然而细菌群落谱并非如此，这表明选择压力能够塑造基因盒库的结构。在46个测序的基因盒产物中，37个是新序列，而9个与数据库序列相似的基因盒主要与假设蛋白相似。1类整合子在环境细菌群落中普遍存在且丰度较高，这表明这组MGEs在获取各种基因盒方面可发挥重要作用，而不仅仅是在临床细菌中介导多药耐药性方面已显示出的影响。
