发布者：抗性基因网 时间：2020-03-24 浏览量：758
摘要
背景：土壤细菌自然产生抗生素作为一种竞争机制，伴随着一系列抗生素耐药机制的进化，并通过水平基因转移进行交换。土壤系统中细菌抗性元素的调查主要来源于受人类影响的环境，而来自偏远和原始环境的信息相对较少，在这些环境中，抗性可能包括祖先的基因多样性。
方法： 我们利用鸟枪基因组学研究了未受干扰的麦凯冰川地区17个原始和偏远的南极表层土壤中抗生素抗性基因（ARG）的分布。我们还询问了ARGs与环境ARG序列的系统发育位置，并测试了ARGs两侧是否存在水平基因转移元件。
结果：共鉴定出177个自然存在的arg，其中大部分编码单药或多药外排泵。氨基糖苷类、氯霉素和β-内酰胺类抗生素灭活的耐药机制也很常见。革兰氏阴性菌含有大部分arg（71%），革兰氏阳性放线菌和硬壁杆菌（9%）的基因较少（9%），反映了土壤的分类组成。值得注意的是，每个样品的ARGs丰度与物种丰富度呈极强的负相关（r = - 0.49，P <0.05）。这一结果，加上ARGs两侧缺乏可移动的遗传元素，表明这些基因是古代水平转移事件的获得。
结论：在这些偏远和未受污染的土壤中，arg很可能代表了功能高效的历史基因，这些基因在过去几代人中一直是垂直遗传的。这些原始环境中的历史arg具有很强的系统发育信号，并与其它类似环境中的arg形成了单系群。
Soil bacteria naturally produce antibiotics as a competitive mechanism, with a concomitant evolution, and exchange by horizontal gene transfer, of a range of antibiotic resistance mechanisms. Surveys of bacterial resistance elements in edaphic systems have originated primarily from human-impacted environments, with relatively little information from remote and pristine environments, where the resistome may comprise the ancestral gene diversity.
We used shotgun metagenomics to assess antibiotic resistance gene (ARG) distribution in 17 pristine and remote Antarctic surface soils within the undisturbed Mackay Glacier region. We also interrogated the phylogenetic placement of ARGs compared to environmental ARG sequences and tested for the presence of horizontal gene transfer elements flanking ARGs.
In total, 177 naturally occurring ARGs were identified, most of which encoded single or multi-drug efflux pumps. Resistance mechanisms for the inactivation of aminoglycosides, chloramphenicol and β-lactam antibiotics were also common. Gram-negative bacteria harboured most ARGs (71%), with fewer genes from Gram-positive Actinobacteria and Bacilli (Firmicutes) (9%), reflecting the taxonomic composition of the soils. Strikingly, the abundance of ARGs per sample had a strong, negative correlation with species richness (r = - 0.49, P < 0.05). This result, coupled with a lack of mobile genetic elements flanking ARGs, suggests that these genes are ancient acquisitions of horizontal transfer events.
ARGs in these remote and uncontaminated soils most likely represent functional efficient historical genes that have since been vertically inherited over generations. The historical ARGs in these pristine environments carry a strong phylogenetic signal and form a monophyletic group relative to ARGs from other similar environments.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5824556/