Tn916 is a conjugative transposon (CTn) and the first reported and most well characterised of the Tn916/Tn1545 family of CTns. Tn916-like elements have a characteristic modular structure and different members of this family have been identified based on similarities and variations in these modules. In addition to carrying genes encoding proteins required for their conjugation, Tn916-like elements also carry accessory, antimicrobial resistance genes; most commonly the tetracycline resistance gene, tet(M). Our study aimed to identify and characterise tetracycline resistance genes from the human saliva metagenome using a functional metagenomic approach. We identified a tetracycline-resistant clone, TT31, the sequencing of which revealed it to encode both tet(M) and tet(L). Comparison of the TT31 sequence with the accessory, regulation, and recombination modules of other Tn916-like elements indicated that a partial Tn916-like element encoding a truncated orf9 was cloned in TT31. Analysis indicated that a previous insertion within the truncated orf9 created the full length orf9 found in most Tn916-like transposons; demonstrating that orf9 is, in fact, the result of a gene fusion event. Thus, we hypothesise that the Tn916-like element cloned in TT31 likely represents an ancestral Tn916.

中文翻译：

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从人类唾液宏基因组文库中检测到一种新的、可能是祖先的 Tn916 样元素

Tn916 是一种共轭转座子 (CTn)，是第一个报道的，也是最充分表征的 CTn 的 Tn916/Tn1545 家族。类似 Tn916 的元素具有特征性的模块化结构，并且基于这些模块的相似性和变化已经确定了该家族的不同成员。除了携带编码其结合所需蛋白质的基因外，Tn916 样元件还携带辅助的抗微生物基因；最常见的是四环素抗性基因，tet(M)。我们的研究旨在使用功能性宏基因组学方法从人类唾液宏基因组中鉴定和表征四环素抗性基因。我们鉴定了一个四环素抗性克隆 TT31，其测序显示它同时编码 tet(M) 和 tet(L)。TT31 序列与附件、调节、和其他 Tn916 样元件的重组模块表明，在 TT31 中克隆了编码截断 orf9 的部分 Tn916 样元件。分析表明，截短的 orf9 中的先前插入产生了在大多数 Tn916 样转座子中发现的全长 orf9；证明 orf9 实际上是基因融合事件的结果。因此，我们假设在 TT31 中克隆的 Tn916 样元件可能代表祖先的 Tn916。