Diverse Broad-Host-Range Plasmids from Freshwater Carry Few Accessory Genes
Diverse Broad-Host-Range Plasmids from Freshwater Carry Few Accessory Genes
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DOI：
10.1128/aem.02252-13
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发表时间：
2013-12-01
影响因子：
4.4
通讯作者：
Top, Eva M.
中科院分区：
文献类型：
--
作者：
Brown, Celeste J.;Sen, Diya;Top, Eva M.
广泛的寄主范围自转移质粒通过在系统发育上不同的寄主之间传播基因来促进细菌适应。这些质粒通常有一个保守的主干区域和一个编码对宿主有利的特征的可变附件区域。然而，我们不知道不编码辅助功能的质粒会在自然界中存活得多好。这项研究的目的是表征从淡水水源捕获的质粒的主干和辅助基因含量，而不选择特定的表型或培养它们的宿主。为了做到这一点，使用了三亲配对，这样唯一需要的表型就是质粒动员非接合质粒的能力。根据10个质粒的全基因组序列，只有5个含有可识别的辅助基因区，没有携带抗生素抗性基因。这些质粒属于四个已知的不亲和性组(IncN、IncP-1、Incu和IncW)和两个潜在的新组。其中八种质粒具有广泛的宿主范围，能够转移到α-、β-和伽马蛋白细菌中。由于缺乏抗生素耐药性基因，我们重新采样了其中一个位点，并将捕获的对宿主产生抗生素耐药性的质粒的比例与从当地污水处理厂的污水中捕获的此类质粒的比例进行了比较。从这两个位点捕获的质粒中很少有编码抗生素耐药性的。因此，在淡水栖息地中很容易发现编码没有或未知辅助功能的高度多样性的质粒。问题仍然是，这些质粒如何在这些微生物群落中持续存在。
Broad-host-range self-transferable plasmids are known to facilitate bacterial adaptation by spreading genes between phylogenetically distinct hosts. These plasmids typically have a conserved backbone region and a variable accessory region that encodes host-beneficial traits. We do not know, however, how well plasmids that do not encode accessory functions can survive in nature. The goal of this study was to characterize the backbone and accessory gene content of plasmids that were captured from freshwater sources without selecting for a particular phenotype or cultivating their host. To do this, triparental matings were used such that the only required phenotype was the plasmid's ability to mobilize a nonconjugative plasmid. Based on complete genome sequences of 10 plasmids, only 5 carried identifiable accessory gene regions, and none carried antibiotic resistance genes. The plasmids belong to four known incompatibility groups (IncN, IncP-1, IncU, and IncW) and two potentially new groups. Eight of the plasmids were shown to have a broad host range, being able to transfer into alpha-, beta-, and gammaproteobacteria. Because of the absence of antibiotic resistance genes, we resampled one of the sites and compared the proportion of captured plasmids that conferred antibiotic resistance to their hosts with the proportion of such plasmids captured from the effluent of a local wastewater treatment plant. Few of the captured plasmids from either site encoded antibiotic resistance. A high diversity of plasmids that encode no or unknown accessory functions is thus readily found in freshwater habitats. The question remains how the plasmids persist in these microbial communities.